Vitamin D

Vitamin D is essential.
It is necessary for many systems, including heart muscle contraction, bone maintenance and repair, absorption of calcium and magnesium from the bowel, cancer prevention and infection control.
It is recognised as an invaluable supplement in those parts of the world where climate restricts natural production by the body.
Vitamin D is not a vitamin, because normally, you don’t eat it. Vitamin D is a hormone, because it is made by an organ (the skin) and transported in the blood to other organs, where it produces beneficial changes.

HOW YOUR BODY MAKES VITAMIN D

The Vitmin D saga is complicated:
The lower layers of the skin use UVB from sunlight to convert Cholesterol into an inactive prohormone called Cholecalciferol.
The blood takes the Cholecalciferol to the liver, where it is changed into Calcifediol.
Calcifediol is transported in the blood, from the liver to the kidneys.
The Kidneys turn it into Calcitriol, the active Vitamin D hormone.
Finally, the Calcitriol travels from the kidneys via the bloodstream to every cell of every organ, to do its work.
 

WHERE DOES VITAMIN D WORK, MOSTLY?

Vitamin D is a hormone, active everywhere in the body.
It is most famous for its special care of the bones (remember the story about all the poor kids in London getting rickets because windows were taxed?) …… People bricked up their windows to save on tax and the sunlight couldn’t get in, so all the children were Vitamin D deficient….
The kids didn’t grow to full height and their bones were too soft, so they got bow legs.
Anyway ……
Vitamin D is essential. It takes part in most chemical reactions inside the cells, so it takes an active part in almost all our functions. Its deficiency has been associated with increased risks of cancers, heart disease, MS, rheumatoid arthritis, type 1 diabetes and many other diseases and malfunctions.

WHAT’S D3’S MOST IMPORTANT JOB?

That’s hard to say: Vitamin D really is everywhere you look!
Perhaps the most interesting (if not the most important) work done by Vitamin D is regulation of so-called “Antimicrobial Peptide Genes”. These genes produce “Histatins, “Cathelicidins” and “Defensins”*, which are internal antibiotics.
They target bacteria, viruses**** and funguses, but also function as signalling molecules which activate the immune system, attracting white blood cells to sites of infection.

VITAMIN D TOXICITY (?)

Much has been said about the “toxicity” of Vitamin D: Vitamin D overdose Is rare, but when it happens, it causes hypercalcaemia (high blood calcium), which can produce calcium deposits in organs like kidneys, liver, saliva glands, heart and muscles.
The main symptoms of vitamin D overdose are those of hypercalcemia, including loss of appetite, nausea and vomiting, then excessive thirst and high urine production, weakness, insomnia, nervousness, itching and rarely, kidney failure.
Because of this possibility, doctors are reluctant to encourage supplementation with more than token doses of this supremely important vitamin.
However the current consensus is that one would need to take 50,000 units of Vitamin D daily for 6 months, to run into problems with side effects.
In my opinion, taking vitamin D is essential: everyone should take between 3,000 and 5,000 international units of vitamin D3** daily***, year-round.
I say “year-round” because we get no direct sunshine in Winter and in Summer light-skinned people, whose skin absorbs more UVB and makes more Vit. D, avoid the sun, while dark-skinned people, whose melanin blocks UVB, need stronger sunshine than we get here.
 
* Defensins and Cathelicidins are chemical attractants for white blood cells and in addition, they promote production of “cytokines” and “chemokines” which attack germs.
** Take “D3”, the active Vitamin D, with a “fatty meal”.
*** At any time of day
*** Vitamin D is fat soluble, so you need fat or oil in the diet, to encourage absorption. Vegetarian diets contain very little fat, so vegetarians are more prone to deficiency.
**** We “catch a cold” when there isn’t enough sunshine to make Vitamin D.
Without the Vitamin D, we run short of Cathelicidins and Defensins: then our ever-present nose viruses are able to take advantage of our weakness. *****
***** If you feel as though you have caught a “cold”, take an extra dose of D3.

I find that taking D3 at bedtime relieves nasal congestion: I go to sleep more easily.

Q: Why don’t you catch cold on sunny days?
A: Because your body makes Vitamin D!

Special note, Re Histatins, Cathelicidins and Defensins: this is where COVID 19 comes in: see a 2005 paper, “Human antimicrobial peptides: defensins, cathelicidins and histatins”,
by Kris De Smet  ¹ , Roland Contreras, PMID: 16215847DOI: 10.1007/s10529-005-0936-5,
at https://pubmed.ncbi.nlm.nih.gov/16215847/