Vitamin D autocrine signaling - illustrated explanationRobin Whittle firstname.lastname@example.org 31 December 2020
(First established 2020-11-23.)
../ To the main page of this site.
Almost all of the numerous (hundreds) of functions of the vitamin D compounds in the body are through autocrine (within the one cell) signaling, and the simple extension of this which is paracrine signaling (signaling to nearby cells). All the immune system functions of vitamin D work in these ways.
This is unrelated to the one hormonal function of vitamin D, which is a very low, but tightly regulated, concentration of circulating 1,25OHD to control calcium-bone metabolism.
Yet most people - including many doctors - are not familiar with
autocrine or paracrine signaling. To understand vitamin D
in general - and especially to understand why population-wide vitamin D
repletion targeting 40 to 60ng/ml 25OHD vitamin D blood levels (100 to 150nmol/L) is the key to improving health - we need a good understanding of vitamin D autocrine signaling.
As far as I know, all this is correct, since it is based on some
earlier text which met with the approval of a senior vitamin D
researcher. If you spot any errors or can suggest any
improvements, please let me know.
||D3 cholecalciferol, 25OHD calcifediol and 1,25OHD calcitriol.
1,25OHD for calcium-bone metabolism is at a much lower level than the
1,25OHD generated as an autocrine agent and/or paracrine agent in
immune and other cells, so the hormonal 1,25OHD levels, which are quite
stable, have no significant effect on the autocrine and paracrine
signaling systems of numerous types of cell.
||Numerous reasons why we should aim for at least 40ng/ml (100nmol/L) 25OHD blood levels.
||2014 research which indicates we should aim for at least 55 or 60ng/ml 25OHD blood levels.
of autocrine signaling with two examples from research articles, the
second of which is directly relevant to severe COVID-19.
Paracrine signaling is easily understood as an extension of this to
D3, 25OHD and 1,25OHD - the three main vitamin D compounds
One definition of the term "vitamin D"
is to refer only to D3 cholecalciferol and/or D2 ergocalciferol.
These are essential nutrients except that D3 can be made by UVB skin
exposure. D2 is inferior to D3 so I won't mention it
further. In this terminology, the two compounds created in
the body from D3 are not referred to as "vitamin D".
However, they have "vitamin D" as part of their chemical names: 25-hydroxyvitaminD
(sometimes with a 3
on the end).
I follow common usage and use the term "vitamin D" to refer
collectively to the three compounds of interest: D3, 25OHD and 1,25OHD.
This is produced by 295 to 297 nanometre wavelength UV-B light acting on 7-dehydrocholesterol in the
skin. It can also be ingested in food or supplements. While this plain D3 directly
protects the endothelial cells which line our blood vessels [Gibson et al. 2015
all its other currently known roles in the body rely on it being
converted in the liver, over a period of days to a week, by the enzyme vitamin D 25-hydroxylase
(encoded by the CYP2R1
gene, a name sometimes given to the enzyme itself) to 25OHD.
(Another enzyme encoded by the CYP27A1 gene does the same thing and so
produces some of the 25OHD.)
The numbers indicate carbon positions. Most hydrogen atoms are
not shown. The special trick to producing this from
7-dehydrocholesterol is to use 295 to 297 nanometre UVB light to break
a ring between carbon 9 and 10.
= 25 hydroxyvitaminD3 = cacldiol [W
This has an OH oxygen-hydrogen hydroxyl group at the 25 position, in
place of the H (not shown) which was there. 25OHD circulates in
the blood, mainly
bound to the vitamin D carrier protein and albumin. It is also
absorbed into fatty tissue, as is D3. Vitamin D blood tests
measure the total bound and unbound level of 25OHD. This level is
the most important part of the whole vitamin D system.
Neither D3 nor 25OHD bind strongly to the vitamin D receptor [W
] which is a complex protein far bigger than these molecules.
] = 1,25 dihydroxy vitamin D = 1,25(OH)2 vitamin D, is produced by a second enzyme
, encoded by the CYP27B1
gene, which adds an OH hydroxyl group at the 1 position to 25OHD.
This happens in the kidneys and inside many types of cells, including
1,25OHD binds strongly to, and so activates, the vitamin D receptor.
There is another enzyme CYP24A1 which
can add an OH hydroxyl group to the 24 position of 25OHD and 1,25OHD,
which is an
irreversible process. The resulting molecules are degraded and
excreted. The activity of this enzyme scales up with increasing
circulating 25OHD levels, and so gives rise to a strong self-limiting
process which reduces high 25OHD levels. This accounts for the curves in
the 25OHD by bodyweight and D3 intake graph from Ekwaru et al. 2014 at 01-supp/a-ratios/
self-regulation makes it very hard to attain potentially toxic 25OHD
levels. Above 150ng/ml (375nmol/L) there is a risk of
Autocrine, paracrine and endocrine (hormonal) signaling
Firstly, a description of the one
hormonal function of the vitamin D compounds. A hormone is a
compound in circulation, whose level (concentration)
Carefully regulated, very low, levels of 1,25OHD
are produced in the kidney from
25OHD and are put into circulation in the blood as a hormone to regulate calcium-bone
This hormonal 1,25OHD has a half life of around 6 hours, which is much
shorter than the month or so half life of 25OHD (or shorter with higher
concentrations and longer if the levels are very low, such as below
In one study
, 25OHD levels averaged 36ng/ml
(91nmol/L 36 parts per billion by mass), which is quite a good level,
and around twice what people attain without much high elevation direct
sunlight skin exposure or proper vitamin D supplements. (There is
little D3 in food or multivitamins, and the UK's 0.01mg 400IU a day is
a scandalously small amount.) The kidneys convert enough
circulating 25OHD into 1,25OHD to maintain whatever level of circulating
(hormonal) 1,25OHD is needed throughout the body to maintain proper
calcium levels in the blood, which are sensed by the parathyroid glands
to the control parathyroid hormone level, which controls the kidneys'
conversion rate. As long as 25OHD levels are above about 20ng/ml,
the kidneys will have no trouble converting it fast enough to maintain
the desired circulating 1,25OHD level.
In this study, the average circulating (hormonal) 1,25OHD level was 0.045ng/ml
(45 parts per trillion, 0.111nmol/L, which is 1/800th of this 36ng/ml 25OHD level
So every 6 hours the kidneys convert about 1/1600th of the circulating
25OHD into circulating 1,25OHD. Over a month, this requires about
1/12th of the circulating 25OHD. Since the half life of this
circulating 25OHD is a month or so, we can guesstimate that about 1/6th
of 25OHD lost every month is due to conversion in the kidneys to
hormonal 1,25OHD. The other 5/6th of the loss must be due to its
use in autocrine (and sometimes paracrine) signaling in many cell types
all over the body, and to the 25OHD being degraded by the
If 25OHD levels were very low, such as 10
(which is disastrously common all around the world), then the kidneys
would generally maintain their 1,25OHD conversion to maintain the level
required for proper calcium-bone metabolism, but the
autocrine/paracrine signaling systems of numerous cell types, including
all type of immune cell, would not be working properly, and so would
consume less 25OHD per month, with very little being degraded by the
However, this would not work quite so well and adults would be at risk of osteoporosis. 25OHD levels of 10ng/ml
or less in children causes rickets - failure of the bones to grow strong and straight.
So at healthy levels such as 40 to 80ng/ml
we can assume that (very approximately) only a tenth or less of the
25OHD produced from D3 is used by the kidneys for the one hormonal
function of the vitamin D compounds.
While hormonal 1,25OHD is the best known role of the vitamin D
compounds, it is not where most of the D3 (converted to) 25OHD vitamin D
is used. Kidney conversion to hormonal 1,25OHD was the only known
use until about 1979 when extra-renal (outside the kidneys) conversion
to 1,25OHD was first discovered (Gray et al. 1979
). In 2007 an important article was published, discussing vitamin D autocrine and paracrine signaling:
These researchers used some macrophages and monocyte derived dendritic
cells, both with their autocrine/paracrine signaling systems turned on,
to find out how their conversion of 25OHD to 1.25OHD was affected by
differing levels of 25OHD: 2, 20 and 60ng/ml. The levels of
1,25OHD produced, after 48 hours, were (Fig 1 levels divided by 2.5 to
give ng/ml) approximately 0.013, 0.12 and 1ng/ml
The 0.012ng/ml 1,25OHD (resulting from 20ng/ml 25OHD supply to the
cells) only marginally affected the gene transcription and protein
synthesis which autocrine signaling in the macrophages drives.
This is upregulation of CD14 [WP
] and downregulation of three other proteins (Fig. 2). The 1ng/ml
1,25OHD level, produced when 60ng/ml
25OHD was supplied to the macrophages) fully upregulated CD4 and
downregulated the other three proteins - the effect was just as strong
as when 40ng/ml 1,25OHD was added to the cells.
Some important points arise from the abovementioned research:
- Researchers in 2007 determined that 25OHD levels at the cells needed to be more like 60ng/ml than 20ng/ml
for autocrine signaling to work properly. Since 25OHD diffuses to
all cells (where it is consumed by autocrine/paracrine conversion to
1,25OHD and slowly, by 24-hydroxylase which consumes a little of it and
degrades 1,25OHD, keeping its intracellular levels low when none is
being created there from 25OHD) from the bloodstream, it follows that
blood 25OHD levels need to be more like 60ng/ml than 20ng/ml for good health.
- Now, in 2020, we know that all types of immune cell need 25OHD
for their autocrine/paracrine signaling systems - and that an unknown
number of other cell types need it too for the same reason. Yet
still, despite increasingly desperate protests from some MDs and
researchers, in the midst of the COVID-19 pandemic, many government
official guidance documents on D3 supplementation are still based on
the outdated (and even at the time, mistaken) 2010 conclusions of the
US Institute of Medicine ../01-supp/#iom , which seek only to achieve 20ng/ml as needed for bone health, with no regard to the higher levels needed for good immune system health.
Please pay attention to these numbers. In other pages here you
can read arguments that if everyone supplemented D3 to attain, on
average, around 50ng/ml
25OHD, that SARS-CoV-2 would only rarely cause severe symptoms, with
those infected shedding much fewer viruses on average, causing
transmission to be much lower than today - so there would be no COVID-19
pandemic, or at least not one to worry much about.
- The hormonal, circulating, 1,25OHD level of around 0.045ng/ml can
be expected to diffuse into cells which use 1,25OHD as part of their
autocrine signaling systems. This is not enough to significantly
activate the gene transcription changes of the autocrine/paracrine
signaling systems, since they are only marginally activated by
0.12ng/ml and it takes about 1ng/ml to fully activate them.
So while all these cells are bathed in hormonal 1,25OHD, the exact
level of this, which is generally stable, is too low to affect their
autocrine signaling systems.
There is room for improvement in the vitamin D research literature, including resolution of the following problems:
- Many MDs and researchers use "vitamin D" to refer only to D3 -
and sometimes they use the term also to refer to D3, 25OHD and 1,25OHD
collectively. This latter definition is the only reasonable one,
since the "vitamin D receptor" only binds strongly to 1,25OHD (not to
D3) and the "vitamin D binding protein" in the blood binds to 25OHD and
1,25OHD, not strongly to D3. The "vitamin D" == D3
definition leads to tortuous and confusing terminological problems and
should be avoided.
- Many MDs and researchers think - and write - that "vitamin D is a
hormone". By either of the two definitions just mentioned this is
incorrect. Only 1,25OHD can act as a hormone, and this is only
when it is created in the kidneys to go into circulation. 1,25OHD
created in autocrine/paracrine signaling is functioning as an autocrine
agent / paracrine agent - which is totally different from what a
- Many MDs and researchers have no idea what autocrine and
paracrine signaling is! They think that vitamin D (the
collective definition, or at least 1,25OHD) "modulates" immune cells'
behavior solely by way of the 1,25OHD produced in the kidneys.
This is absolutely not the case, and it is a very serious
misconception. See, for instance, Figure 1 of Newmark et al.
This is an interesting article (I could follow it to about page 6)
about the evolution of the vitamin D systems. However, the
diagram showing 1,25OHD going from the kidneys to the immune cells is just plain wrong.
- It is common to write of people being vitamin D sufficient,
insufficient and deficient, as if there is consensus on what this
means. Generally it means > 30ng/ml, < 30ng/ml and
<20ng/ml respectively. The question of healthy levels is a
matter of debate - and it can't be assumed that there is a single
healthy level for all people. Maybe some individuals need more
(MS sufferers certainly do) - and some classes of people may need
more. Perhaps 25OHD levels are only part of what constitutes good
health and other factors, such as Vitamin D Binding Protein
characteristics and concentrations really matter too.
Ordinary blood tests are for total circulating 25OHD, and most of it is
bound tightly to VDBP or loosely to albumin, which reduce its
availability for diffusion to many cell types.
Researchers should report the proportion of people whose 25OHD levels
are below 30ng/ml and above 20ng/ml or whatever, not just that they
"are vitamin D insufficient".
Circulating 1,25OHD is the one hormonal function of the vitamin D
compounds. A hormone
] is a
compound which performs signaling between cells, over the whole body,
by being transported everywhere in the bloodstream. This is endocrine
signaling AKA hormonal
occurs entirely within a particular cell, and so is unrelated to
hormones or endocrinology. It is not used to regulate
or slowly changing processes - as is usually the case with hormonal
signaling - but to enable an individual cell to respond rapidly
and fully to
particular conditions. Vitamin D autocrine signaling involves
external conditions causing 25OHD to be converted into 1,2OHD within
the cell, which activates vitamin D receptors within
cell (or perhaps the cell's own receptors, but embedded in the cell
membrane and binding with 1,25OHD outside the cell, where that 1,25OHD
has been created from 25OHD inside this cell), some of which migrate to
(or at least passively diffuse into) the nucleus [WP
] and alter gene expression [WP
], thereby causing this particular cell
to respond to the new circumstances. 25OHD is consumed in this
process. This 1,25OHD is functioning as an autocrine agent.
is an extension of autocrine signaling in which some of the 1,25OHD
diffuses out of the cell and into the interstitial fluid between cells,
where it can affect the behaviour of other cells (probably different
types of cell from the one in which the 1.25OHD is created) which are
nearby. This does not occur by this 1,25OD being transported long
distances via the bloodstream. Here, the 1,25OHD is functioning as a
paracrine agent. (Juxtracrine signaling is like paracrine signaling, except that the
diffusion is only to adjacent cells.)
In one case at least (I can't remember which type of immune cell) the
cell produces 1,25OHD as described for autocrine signaling but seems to
have little or no vitamin D receptors in itself. So it seems to
be producing it purely for paracrine signaling to adjacent cells of
Sidebar on intracrine
In the past the term
"intracrine" was used alongside "autocrine" with the former meaning
what we now know as "autocrine" in most respects, and "autocrine"
meaning the same thing but with the receptor being on the outside of
the same cell, rather than inside the cell. As far as I know,
hardly anyone cares about this distinction in 2020 and "autocrine"
covers both receptor
locations. A good introduction to autocrine signaling from 2010,
in which the term "intracrine" is used instead, is Martin Hewison's Vitamin D and the intracrinology of innate immunity https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2854233/
This knowledge of vitamin D autocrine signaling has been developed
mid-2000s. As far as I know, there are no accurate estimates of
many types of cell use vitamin D autocrine or autocrine-paracrine
signaling. All types of immune cell use this as you can
read in the Charoenngam & Holick article linked to below.
For more in-depth material, a good place to start might be articles which cite
a 2010 article, Autocrine and Paracrine Actions of Vitamin D
by Howard A Morris and Paul H Anderson. Also: Vitamin D metabolism and signaling in the immune system
), Vitamin D and immune function: autocrine, paracrine or endocrine
) and Vitamin D and immune function
). These processes were not always described as "autocrine" or "paracrine", but these are the proper terms to use now.
At least 40ng/ml 25OHD blood levels required for good immune system function
The importance of proper (at least 40ng/ml
= 100nmol/L = 1 part in 25 million by mass) levels of 25OHD is not
widely enough known. While lower
values may be sufficient for the kidneys to maintain the proper level of hormonal 1,25OHD, we need
at least this level of 25OHD for numerous types of cell - especially
immune cells - to function correctly.
The target range of 40 to 60ng/ml (100 to 150nmol/L)
was stated in 2008 by 48 leading researchers and MDs in the Call to D*Action: https://www.grassrootshealth.net/project/our-scientists/
and by this recent review article:
Immunologic Effects of Vitamin D on Human Health and Disease
Nipith Charoenngam, Michael F. Holick 2020-07-15
Nutrients 2020, 12(7), 2097
This article and another one:
of Vitamin D’s Calcemic Activity and Non-calcemic Genomic Activity and
Individual Responsiveness: A Randomized Controlled Double-Blind
Arash Shirvani, Tyler Arek Kalajian, Anjeli Song & Michael F. Holick, Nature Scientific Reports 2019-11-27
report on hundreds of genes which are upregulated or downregulated by
vitamin D in a sample of white blood cells. Below, I explain how
the upregulation occurs, but not the downregulation since I don't yet
understand the molecular mechanisms. All these genes are affected as
part of autocrine/paracrine signaling in an unknown number of cell
types, including all immune cell types. I am not sure to what
extent anyone has surveyed such genes in cell types normally found in
tissues, and which are not normally circulating in the blood.
So there seems to be a large and so-far undefined number (I guess
dozens to hundreds) of cell types who respond to their circumstances in
part, at least, via vitamin D based autocrine/paracrine signaling.
This means vitamin D (the three compounds in general, but in the cells
themselves, just 25OHD and 1,25OHD) are extraordinarily important for
most or all systems of the body. The scope of vitamin D's role in
the body extends beyond the proteins for which these specific genes
provide the instructions, because some of these genes involve proteins
which affect histones [WP
]. Histones are proteins which
physically organise the long DNA molecules of the chromosomes, 1.8
metres in total. An important role of the histones is to unwind
particular regions of the DNA so its genes can be copied into messenger
RNA molecules and so direct the cell's protein making machinery.
To whatever extent vitamin D autocrine/paracrine signaling affects
histones, it therefore affects numerous other aspects of the cell's
ability to perform its functions.
40 to 60ng/ml (100 to 150nmol/L)
was also suggested as the proper target range in this 2019 article (24 citations
Please also see the recent article from MDs in Dubai who had great
success with COVID-19 patients by either previously raising their 25OHD
levels to the 40 to 90ng/ml 100 to 225nmol/L
levels or by using the same bolus D3 and then body-weight ratio
continuing supplemental D3 intakes on newly diagnosed hospitalised
COVID-19 patients. The link and my summary is at: https://aminotheory.com/cv19/#2020-Afshar
Here is another recent research article:
Editorial – Vitamin D status: a key modulator of innate immunity and natural defense from acute viral respiratory infections
A. Fabbri, M. Infante, C. Ricordi Eur Rev Med Pharmacol Sci 2020; 24 (7): 4048-4052 2020-04-05
They mention that 40 to 60ng/ml circulating 25OHD
is required for the autocrine signaling system of immune cells to function properly
The text (in the quote below) "the beginning point of the plateau where the synthesis of the active form calcitriol becomes substrate-independent
requires some explanation for non-specialists. The 1-hydroxylase [WP
] enzyme is a
large, complex protein, whose actions are powered by some other
molecules which are changed in the process. The authors are
discussing the conversion of 25OHD to 1,25OHD, which is a crucial early
step in autocrine signaling. There are multiple 1-hydroxylase enzyme
molecules in the cell, and each converts one 25OHD molecule at a time
to 1,25OHD. The speed of this conversion is important,
since if it is too slow, then the 1,25OHD levels in the cytosol (main
body of the cell, where this happens - not in the nucleus) will not
raise to a high enough concentration (as noted above, around 1ng/ml
(1 part per billion by mass) that a sufficient number of these
1,25OHD molecules will bind with vitamin D receptor molecules, after
which some of these bound complexes migrate (or at least diffuse) to
the nucleus, as I will describe
There are a few
24-hydroxylase enzyme molecules in the cell, converting any 1,25OHD
they find to inactive 1,24,25OHD which is broken down into compounds
which are excreted. (This enzyme does the same thing to the more
numerous 25OHD molecules in the cell: convert them to 24,25OHD which is
broken down and taken away.) This serves two
purposes. Firstly, mopping up any hormonal (from the bloodstream)
1,25OHD which diffused into the cell, to reduce the degree to which it
might activate the rest of the autocrine signaling system.
Secondly, to slowly mop up 1,25OHD previously produced by the autocrine
signaling system operating normally, so that the levels drop after it
is no longer activated. In a further twist, some of these
enzyme molecules are formed differently and don't convert 25OHD or
1,25OHD, they just bind to them for a while and so are described as decoys
et al. 2015, and also Hewison et al. 2007, above.]
If there is no 25OHD, obviously the autocrine signaling system cannot
work. If there is too little, then it will work too slowly, or
not work properly - so the cell will not respond fully to its new
circumstances and our health will suffer.
The enzyme itself is not changed - it is a catalyst. When,
by random thermal motion, a molecule of 25OHD is in the right position
in the enzyme's active site, the enzyme replaces the H in the 1
position with an OH hydroxyl group, at which time the newly-formed
1-25OHD is no longer so attracted to the enzyme's active site, and floats
The 25OHD molecule, up to the point where it is converted to 1,25OHD, is the substrate
The authors imagine a graph with 25OHD concentration being the
horizontal axis and the total rate of conversion to 1,25OHD being the
vertical. The plateau
they refer to is where the rate of conversion no longer rises linearly
(upwards and to the right) with 25OHD concentration, due to the limiting factor being mainly the
enzyme's own intrinsic speed of conversion, when it has it hardly as to
wait for a fresh 25OHD molecule to arrive in its active
We also believe that maintenance of circulating 25-hydroxyvitamin D levels of 40 - 60ng/ml would be optimal, since it has been suggested that concentrations amounting to 40ng/ml represent the beginning point of the plateau where the synthesis of the active form calcitriol becomes substrate-independent [2011-Hollis err] [2018-Wagner].
Additionally, serum 25-hydroxyvitamin D levels of approximately greater than or equal to 40ng/ml
could provide protection against acute viral respiratory infections, as
demonstrated in a prospective cohort study published in PLoS One and
conducted on 198 healthy adults [2020-Sabetta]. To reach these concentrations in adults, a dietary and/or supplemental intake of vitamin D up to 6000 IU/day
– deemed to be safe – is required. However, elderly subjects,
overweight/obese and diabetic patients, patients with malabsorption
syndromes, and patients on medications affecting vitamin D metabolism may require even higher doses under medical supervision.
The authors mean that if 25OHD levels (in the blood) are around 40ng/ml
or more, then this leads, via diffusion - there being no
active transport of 25OHD from the bloodstream into the fluid between
the cells and across the cell's membrane - to a concentration of 25OHD
in the cell to start with which enables the enzyme to work at close to
its full speed converting these 25OHD molecules to 1,25OHD.
Also, this 25OHD level in the blood is required to maintain the 25OHD
levels in the cell as some of the 25OHD is consumed by the conversion
process, so the enzyme is not slowed down by having to wait for a fresh
25OHD molecule to arrive in its active site.
The key thing to remember is that 25OHD levels are very low. A healthy level is 50ng/ml
, but many people, without supplements, never achieve this and average levels 1/5 or even as low as 1/10th of this. 50ng/ml
is only one part by mass of 25OHD per 40,000,000 parts by mass of all
the water and other compounds in the cell. So these are quite
rare molecules. A 70kg person only needs a gram of D3 every
22 years, most of which is converted to 25OHD in the liver, to maintain
this healthy level.
You probably began reading this page thinking of the COVID-19 crisis,
the influenza crisis and perhaps the
. Now you are contemplating lonely 25OHD
molecules being jostled around by the thermal vibrations of surrounding
molecules (mainly water) until one of these molecules:
- Arrives very close to the active site of the much larger enzyme molecule. This is 3
dimensions of movement over large distances (one such molecule on
average per ~320 nanometres cubed) compared to the size of the 25OHD
molecule (~0.2 nanometers) and the enzyme molecule:
- Is pointing in exactly the right direction for it to fit. This needs to be correct in 3 dimensions too.
- Is rotated correctly - this is 1 dimension.
When this happens, the positive and negative changes on particular
parts of the two molecules will draw them closer, the 25OHD will be
fully docked, and the enzyme and its co-factor molecules will do their
work of attaching the OH group.
This probably seems a long way from COVID-19, but it is absolutely germane.
If everyone in the world had 40ng/ml
or ideally 60ng/ml
more 25OHD in their blood, then:
- The enzymes in all their cell types which use vitamin D for
autocrine/paracrine signaling would not be waiting long for another
25OHD molecule to dock.
- So they would produce 1,25OHD at a perfectly healthy rate whenever the autocrine signaling system is activated.
- The autocrine signaling systems of all cell types (including all
types of immune cell) would work correctly, making then respond fully
and rapidly to their changing circumstances.
- Although there are numerous other factors affecting total immune
system performance, this would mean that the current vitamin D
deficiency epidemic would not exist - and it is low vitamin D which is
the primary cause of some immune responses being weak, while others are
dysregulated - meaning overly-aggressive, hyper-inflammatory and
self-destructive. These weak and dysregulated immune
responses are the primary or sole reason why some people who are infected with SARS-CoV-2 develop severe COVID-19.
- So almost all people would fight off the SARS-CoV-2 infection
without serious symptoms. Likewise flu. Also, very few
people would develop sepsis.
(Note: there is a lot of interest in the idea that high vitamin D
levels will substantially reduce the chance of being infected with
COVID-19 for any given vital insult. I see no evidence that
this is more than a slight effect - and I consider it
insignificant. The most important point, for all society, is the
next one, followed by the just-mentioned great reduction in average
- For those infected, average
total quantities of viral shedding would also be greatly reduced, so
fewer people would become infected. COVID-19 would not
spread very much at any time of year. Likewise flu.
- So there would be no COVID-19 crisis, with no need for lockdowns,
social distancing, vaccines or masks. The few who did become
seriously ill could be treated with oral 25OHD and bolus D3 ../01-supp/#25plusD3 as well as other techniques.
You now have an understanding of some a crucial part of the current global crisis down to a
molecular level - and if you want to, you can look up the gory details
of the virus, the ACE2 receptor, the destruction of the endothelium,
the hypercoagulative state of the blood and the microembolisms and
larger clots in the lungs, brain, heart, spinal cord, liver kidney etc.
None of those gory details would matter, because they would not exist,
if everyone had enough vitamin D. 70kg adults, on
average, to attain about 50ng/ml (125nmol/L)
25OHD, without relying on UVB skin exposure, or the small amounts of D3 in food, need to ingest 45 milligrams of D3 year
= a gram every 22 years. This is 0.125mg 5000 IU a day
. Pharma grade D3 costs about USD$2.50 a gram
25OHD requirements for immune cell autocrine/paracrine signaling as indicated by hospital infection rates following surgery
Here is another way of understanding the need for proper 25OHD levels around or above 50ng/ml (125nmol/L)
The following graph comes from research into the risk of infections in
people (all obese) who had just been operated on for Roux-en-Y gastric
This is a weight-loss surgery
with numerous problems due to malabsorption of fats, iron, and other
nutrients including vitamin D3 and due to overly rapid, uncontrolled,
absorption of carbohydrates. It is highly regarded, and those who
do it are morbidly obese, but it seems crazy to me when they should
first try suitably high D3 intakes and all other measures to improve
their health and reduce their life-threatening obesity: robust
supplements for all micronutrients including especially vitamin D3, no
fructose, no caffeine and so less need for alcohol, nicotine and
anti-depressants / anxiolytics - to reduce their obesity.
This PNG is from my Inkscape version combining two similar graphs, made from the vectors in the PDF:
The graphs depict how the risk of infections in hospital - either
directly resulting from the surgery or due to other reasons - vary with
vitamin D 25OHD levels, for 770 patients.
Low rates of infections occur when the immune system's innate responses
are functioning properly. The failures are due to weak immune
responses which directly combat pathogens, as in the first autocrine
signaling example below. (The second McGregor et al. example
below concerns innate immune system regulatory lymphocytes which, when
their autocrine signaling fails due to lack of 25OHD, cause trouble by
producing pro-inflammatory cytokines. This failure either causes
or at least strongly drives severe COVID-19, but is not likely to be
important in the infections in hospital which are the subject of
Quraishi et al.'s research.)
With one potential exception, wherever
the graphs rise above about 0.03, this is due to autocrine signaling
not working properly in some - probably many - types of immune cell
The exception is that that the higher D3 levels which give rise to the
higher 25OHD levels are also directly useful (without involving
autocrine signaling) in the protection of endothelial cells [Gibson et al. 2015
I have not been able to quantify how important this is, and I suspect
the main cause of these infections is the failure of the innate immune
system to rapidly defeat bacteria.
The raised levels in the graphs pretty much directly indicate
dysfunction of autocrine/paracrine signaling due to inadequate
25OHD. Eyeballing this we see that the 40ng/ml
minimum recommendations mentioned above don't go quite far
enough. The evidence of this substantial research (770 subjects,
in one hospital, with all the researchers being from Harvard Medical
School) indicates that we should be aiming for at least 55ng/ml
, at least in these obese adults.
Please think of these graphs whenever you read of individual and
average 25OHD levels in people who are not adequately supplementing D3
and who do not get very substantial UVB skin exposure (which damages
DNA and which I do not recommend). Their levels are typically
The following description is mainly
of autocrine signaling, using vitamin D (25OHD being converted to 1,25OHD). Paracrine signaling is easy to understand
as an extension of this.
Step 1 - producing vitamin D receptor and 1-hydroxylase enzyme molecules
The diagrams below are adapted from a diagram in this 2011 article
which has a good description of vitamin D autocrine signaling in a particular type of immune cell, although
the term autocrine is not used:
Here is a description of autocrine signaling which assumes an interest
in cell biology, but little prior knowledge. In this
example from Martin Hewison, we learn how toll-like receptors [WP
] on the
cell membrane of some types of monocytes [WP
- in this case a macrophage [WP
] respond to bacterial infections. The same principles of vitamin D
autocrine signaling apply to other types of cell, including the Th1
regulatory lymphocytes discussed below (McGregor et al.), although the
stimulus for activating autocrine signaling is totally different to
the bacterial fragments in the current example, and the response of the
lymphocyte is also entirely different.
In this cell type, fragments of pathogens activate toll-like receptors which are embedded [WP
] in the cell membrane, and which change their shape so the part of the
molecule inside the cell (in the cytosol) causes some other signaling
molecules to migrate to the nucleus and upregulate the transcription
two genes: for the 1-hydroxylase enzyme and for the vitamin D receptor (VDR) protein.
Those signaling molecules are cell-type specific, and somehow cause transcription enzymes to make mRNA (messenger RNA [WP
copies of the information in those genes. These multiple
mRNAs migrate out of the nucleus, to the cytosol, where they are found
by ribosomes [WP
which work along each mRNA, following its instructions of which amino
acids to assemble into the protein chain. This is called translation
When each ribosome reaches the other end of the mRNA, it has
one chain, which folds of its own accord to become a complete single
molecule of protein. This creates some number (I guess hundreds)
of complete, operational, 1-hydroxylase enzyme molecules and
likewise vitamin D receptor molecules.
Step 2 - converting 25OHD to 1,25OHD molecules and these binding to vitamin D receptor molecules
25OHD is carried in the blood plasma primarily bound to vitamin D binding proteins [WP
], with a lower proportion bound less strongly to albumin [WP
] proteins. A small proportion of these 25OHD molecules (red
discs) are free to diffuse from the plasma, into the interstitial fluid
between cells (in the case of cells which are not in the bloodstream or
in the walls of blood vessels) and then they diffuse
across the cells' lipid bilayer [WP
] plasma membrane into the cytosol of the cell.
D3 has only one hydroxyl group, in the 3 position with all its other
sides made up of hydrogen atoms. So it is soluble in oils but not
much in water. 25OHD has two hydroxyl groups and so is more
soluble in water.
Once the newly created 1-hydroxylase enzymes start appearing in the
cytosol, assuming there is an adequate concentration of 25OHD molecules (red
discs) - which there will be if blood levels are 40ng/ml
or more - then it doesn't take long for one of these 25OHD molecules to
find its way to the active site of the enzyme molecules, be
hydroxylated at the 1 position, and be ejected back into the cytosol as
1,25OHD molecules, (green
By now there will be some number of vitamin D receptor VDR molecules and
the freshly made 1,25OHD molecules find their way (as described above,
with random thermal motions and rotations) into the active site of one of these receptors, where
the two are strongly attracted and stick together as an activated
This newly produced 1,25OHD is functioning as an autocrine agent which binds to these vitamin D receptor molecules.
This step is identical for the vitamin D based autocrine signaling systems of all cell types.
Step 3 - Activated receptor complexes diffuse or migrate to the
nucleus where they alter gene transcription and so protein translation
When a 1,25OHD molecule binds to the
receptor molecule, this changes the shape of the receptor molecule and
causes some of them to migrate into the nucleus. (I guess only a
subset of them migrate to the nucleus, so perhaps is is diffusion,
rather than them all marching off in the direction of the
There, some subset of the activated receptor complexes find their way
(by diffusion, I guess) to another molecule (retinoid X receptor [WP
not shown in these diagrams) with binds to them as well
and the entire heterodimer complex then finds its way to particular
patterns of DNA which are exposed (according to how the DNA of the
various chromosomes are wrapped around and otherwise organised by
]) and ready to accept them. These are the VDRE (Vitamin D Response Elements [WP
and they are upstream of a particular gene which this process is
intended to increase or decrease the copying of. (The whole human genome
has thousands of such genes, with a VDRE upstream. By various
means, each cell type exposes only these to being bound by the
heterodimer complex - the particular genes which this cell needs to be
copied in order to respond to its circumstances properly.)
Once the VDRE section of DNA has the heterodimer attached, in some circumstances this
signals DNA copying enzymes to start work there, copying the data in
the downstream gene into messenger RNA molecules. In others, it reduces the amount of copying of this gene.
In principle, if this process of activated receptor complexes finding
their way to these transcription regulator molecules was highly guided,
then there would only need to be a handful of 25OHD molecules converted
to 1,25OHD, perhaps by a single or a few enzyme molecules, and likewise
there would only need to be a handful of vitamin D receptor molecules.
However, since the processes are unguided (diffusion) or at least not
very efficient, and since the activated complexes and probably the
1,25OHD molecules would have relatively short half-lives (of their own
accord, or by enzymes breaking them down, to get rid of them once the
conditions which activated autocrine signaling no longer occurred) then
there needs to be quite a quantity of both 1,25OHD and vitamin D
molecules ready to bind together. This requires continual
conversion of 25OHD to 1,25OHD, since the 1,25OHD molecules have
relatively short half-lives. As noted above, to fully alter the
gene translation process, it seems there needs to be around 1ng/ml
(1 part per billion by mass) 1,25OHD in the cytosol of the cell.
- There an unknown number of cell types using vitamin D
for autocrine signaling.
- There are likely countless billions
of each such cell type.
- The autocrine signaling systems of each cell of these types is activated
at least some of the time .
- Only a subset of the 25OHD is
actually used by autocrine/paracrine signaling, one might expect the total D3
requirements per year to supply this 25OHD to be substantial. But
0.045 grams per year is all it takes for 70kg adults to maintain, on average, about 50ng/ml 25OHD.
With upregulated gene copying, the newly copied mRNA molecules
leave the nucleus and go into the
cytosol, where ribosomes run along them, making the proteins they
contain the instructions for. (For downregulation, fewer of these
mRNA molecules are produced than previously.) These proteins are
the ones which
make the cell respond to its changed circumstances. In some
cells, these may be exported to kill pathogens, or to kill infected
cells. In others, the proteins may cause the release of
pro-inflammatory or anti-inflammatory cytokines [WP
] - signaling molecules which control activities of other types of immune cell which are nearby.
The alterations to gene transcription
alter the mix of mRNAs in the
cytosol and so (translation
) the quantities of proteins produced by the
ribosomes which run along them. (mRNAs have quite short lives, so
for continual protein production a continual supply of them via
transcription is required.)
This altered set of protein products is what drives the cell to alter
its behaviour. In this example, the altered behaviour sets the
cell up for engulfing and digesting bacteria.
In the McGregor et al. example below, when the autocrine signaling
systems of a Th1 lymphocyte is activated and works properly, the
lymphocyte stops producing a
pro-inflammatory cytokine and starts producing an anti-inflammatory
One part of paracrine signaling is
depicted at the bottom left of the above diagrams: some of the newly
produced 1,25OHD diffuses out of the cell and reaches nearby
As noted above, the concentration of this 1,25OHD is probably around 1ng/ml
(1 part per billion by mass) when the autocrine signal is is fully
activated and there is sufficient 25OHD to achieve this. This 1ng/ml is much higher than the very low levels of 1,25OHD present in the bloodstream
as a hormone to regulate calcium-bone metabolism, around 0.045ng/ml (46 parts per trillion).
The newly produced 1,25OHD is functioning as a paracrine agent when it
diffuses out of the cell, and makes its way to other nearby cells where
- by one means or another - this increased local level of 1,25OHD is
detected in a way which alters the behaviour of those nearby cells.
The McGregor et al. article on autocrine signaling failing in Th1 lymphocytes due to lack of 25OHD
If most or all of the above makes sense
to you, then you are in a good position to either read the entire
McGregor article, or at least my account of it, at:
Then, you will have a real, cellular and molecular level understanding
of some of the most important reasons why the world is going to hell in
a handbasket at present, with the twin crises of COVID-19 and of the
attempts to protect people from this disease by lockdowns etc.
It would be much easier if everyone took vitamin D supplements to raise
their 25OHD levels to the ancestral levels which enable our vitamin D
autocrine signaling systems to work properly.
I regard this article as the most important in the entire COVID-19 literature
This is my best attempt to describe some complex processes I have no expertise in.
concerns CD4 [W
(T-helper cells, T4 cells) which emit various cytokines to signal to
other types of immune cells actions which destroy pathogens directly,
destroy infected cells (cytotoxic - and so inflammatory and potentially
self-destructive if not properly controlled) or take other actions.
Our Th1 (T Helper 1) cells start off on a pro-inflammatory program, referred to in the article as T-effector
. In this mode, they produce the inflammatory cytokine IFN-γ interferon gamma [W
The autocrine signaling system of Th1 lymphocytes has evolved so that when it is
activated and works properly, the Th1 cell switches to a second mode of operation
(program) in which it instead emits the anti-inflammatory cytokine
]. The above article discusses how this does not happen in Th1 cells from hospitalised COVID-19 patients, due to lack of 25OHD
while it works fine in TH1 cells from healthy controls.
(Unfortunately the authors do not report blood 25OHD levels from these
patients. The corresponding author wrote to me that they did not have access to any such measurements.)
"Complement" here refers to a number of proteins which form an important part of immune system signaling [W
]. High levels of complement occur in the lungs with severe COVID-19.
switch from effector T cells, important for pathogen clearance, into
IL-10 producing cells reduces collateral damage and is a natural
transition in a T cell’s life-cycle. This suggests that IL-10 is
produced by cells that are successfully transitioning into the Th1 shut
down program. . . . We asked whether prolonged Th1 responses in
COVID-19 patients are due to the failure in initiating this Th1
This article is a beauty. It gets
down to brass tacks with the molecular processes of one aspect of the
cytokine storm of immune dysregulation which is crucial to the
development of severe COVID-19. This failure may be the the
biggest single pathological process which causes some people to develop
severe COVID-19 symptoms.
If not, then the similar failures of
autocrine signaling systems in all other immune cells would be the
The high levels of complement activate the CD46 [WP
] transmembrane receptor. This induces (leads to more of) 24 transcription factors [WP
Transcription factors are molecules which bind to specific locations on
the DNA of chromosomes where they enhance or reduce (turn on or off) the transcription
of particular genes into messenger RNA [W
P]. The exact mechanisms of these transcription factors depend on epigenetic [W
changes to the DNA, which would be specific to the particular cell
type. Two of these transcription factors upregulate the mRNAs for
the vitamin D receptor [WP
] (hereafter VDR
) and for the CYP27B1 enzyme
(which I referred to above as the 1-hydroxylase enzyme, though its real
name is more elaborate than this) which adds a hydroxyl group to the 1
position of 25OHD, converting it to 1,25OHD.
In the vitamin D autocrine signaling system of other cell types, some
other types of receptor would be activated initially, in response to
stimulus than high levels of complement. This would result in the
induction of different transcription factors - and in some cases, some
of these first set of messenger molecules in the cell do part of the
work required for the cell to respond
properly to the stimulus. However, two of those transcription
factors would again be for the genes for VDR and the CYP27B1 enzyme,
just as in this
particular example and the one above.
The next few steps are for this example, and more generally for the vitamin D autocrine functions of other cell types.
These two sets of mRNAs migrate from the nucleus and (for simplicity
ignoring any post-translational modifications) find ribosomes in the
work their way along each mRNA and produce a protein according to the
instructions encoded in the mRNA. So, (ignoring any other
processing steps) the cytosol now contains a lot more VDR and CYP27B1
enzyme molecules than it did before.
The next step is what should
happen, but did not happen or did not happen enough in the Th1 cells
isolated from the lungs of hospitalised COVID-19 patients.
25OHD from the bloodstream migrates into the the interstitial fluid [WP
and from there it migrates into the cytosol of the Th1
lymphocyte. The initial and continuing 25OHD levels in the
cytosol of our TH1
cells are determined primarily or solely by passive diffusion from the
concentration in the blood.
By random bouncing around due to thermal motion, a 25OHD molecule finds its way into the
active site of a CYP27B1 enzyme molecule, which, with co-factors,
attaches an OH hydroxyl group onto it and releases it as 1,25OHD
The newly created 1,25OHD bounces around in the cytosol, as do all
small molecules, until it finds itself correctly oriented in the
binding site of a VDR molecule, to which it has a very strong
This pairing is the "activated" state of the VDR. The VDR
molecule changes its behaviour and the entire complex of VDR and its
bound ligand, 1,25OHD, migrates to the nucleus, where it binds to
a retinoid X receptor molecule and the whole heterodimer complex finds its way to
particular parts of the DNA upstream of genes which are to be copied
into messenger RNA molecules, as described above (VDRE). The particulars of which genes
these are differ between the various cell types which
use vitamin D autocrine signaling.
The resulting new mRNAs (and
potentially reductions in previously produced mRNAs) are worked on by
ribosomes and so result new proteins (or less of of other proteins) in
the cytosol which cause the cell to complete the action for which this
autocrine signaling system has evolved.
In this particular example, the cell's actions includes shutting down
production of pro-inflammatory IFN-γ production and ramping up production of inflammatory IL-10.
This does not occur to the degree it should in the cells the
researchers isolated from the lungs of COVID-19 patients - but it did
when they added sufficient 25OHD
for the CYP27B1 enzyme to work on.
This is one example of a specific vitamin D autocrine signaling system
in one particular type of immune cell. The following article
discusses the evolutionary basis and other details of 189 human genes
know to be regulated in an autocrine / paracrene manner by vitamin D in monocytes [WP
], which are a subset of leucocytes [WP
which are a subset of immune cells which are a subset of the cell types
in the body which use their own particular version of vitamin D
autocrine / paracrine signaling.
I don't want to imply that I have read
this, or that I would be able to understand it without weeks of
work. I cite it as an easy way of expanding upon this one
concrete example which surely plays a crucial role in severe COVID-19
(and see https://aminotheory.com/cv19/#2020-Castillo for how oral
25OHD for hospitalised patients causes most of them to get much better,
very quickly) to indicate how important this general principle of
vitamin D autocrine signaling is.
Why so complex?
Autocrine signaling is quite complex. Inquiring minds want to know why
this evolved and is used for so many cell types. This is a Mouse Trap (video
) approach to biology - Rube Goldberg [WP
engineering when we can imagine something simpler would do
the job. This wacky complexity is a feature of biology - and some
or many of the idiosyncratic features of the evolved systems give rise
to valuable mechanisms.
Why, for instance,
doesn't the sensing of the changed condition lead to direct
upregulation and downregulation of whatever genes the cell needs to
produce (or no longer produce) the proteins which will make respond as
it is meant to?
Sidebar for the really curious:
the answer might be that the evolved capacity of the activated vitamin
D receptor (a singe VDR molecule bound to a 1,25OHD molecule) to
upregulate and downregulate multiple genes turned out be flexible and
useful. The activated receptor complex binds to particular gene
transcription promoter patterns (VDREs) in the DNA which are upstream
of the genes whose rate of copying to messenger RNA is to be up- or
This flexibility and ability to alter multiple genes at once may have
some advantages over the simpler arrangement of, for instance, whatever
signaling system enables an activated toll-like receptor [WP]
to alter gene transcription (a first step in autocrine signaling)
somehow evolving flexibility over multiple types of cell to alter as
many genes in any one cell type, and in so many cell types, as are
altered by the activated vitamin D receptor.
Just to keep us on our toes, in his article, Martin Hewison describes a
separate set of processes operating in parallel to this autocrine
signaling system, also driven by the activation of the toll-like
receptors, which turns on some other aspects of the cell's response.
See also Martin Hewison's article PMC2854233
regarding how the vitamin D autocrine signaling we humans have is
specific to primates, and not found in rodents and other families of
mammals. He estimates this approach to autocrine signaling is
about 40 million years old.
Please also see this article suggesting some hypotheses about the
long-term evolutionary history of the vitamin D compounds and their
receptors, enzymes and binding proteins.
I roughly understood it up to about page 6.
© 2020 Robin Whittle Daylesford, Victoria, Australia