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Vitamin D – Underrated Vitamin?

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Written by   646
9 months ago (Last updated: 8 months ago)


Vitamin D is a group of fat-soluble substances of which more than 10 different ones are known. Of these, D2 (ergocalciferol) and D3 (cholecalciferol) are the most important to humans. They are generally considered as interchangeable – but they are not. D3 has a much stronger effect than D2. As for supplemental vitamin D, one should always take vitamin D3.

Except for in some mushrooms, such as shiitake, this vitamin exists only in animal products like fish, egg yolk, and dairy products. Just as with vitamin A, the richest source of vitamin D is fish liver, which, unfortunately, today is so full of environmental toxins that it should be avoided at all cost. It is very difficult, perhaps impossible, to cover one's need of vitamin D through the diet.

Under certain conditions D3 can be produced by exposing the skin – and its fat – to sunlight. But note that it must be the genuine fat. If you use sun oil, you destroy the preconditions for D3 production. Interestingly, it is cholesterol that is synthesised to vitamin D. (Cholesterol is not always harmful but has its essential functions. Too little cholesterol might be as serious a problem as too much.) Sunscreens and windows also block vitamin D production, and so do heavy air pollution, as in big cities. Also, if you live far from the equator, the sun is too weak to provide vitamin D a large part of the year.

The sun must be strong in order to produce vitamin D. As a rule, you must expose the skin some time between 10am and 2 or 3pm during a time of the year with strong sunlight (any time around the Equator - in the summer in the Northern Hemisphere). It is not enough that the sun is shining.

The time required depends on many factors. But 30 minutes per day ought be enough, if a relatively large part of the body is exposed – and if you have relatively fair skin, no sunscreen or chemicals on the skin, and if the air is not too polluted. Perhaps even 20 minutes is enough. The only way to find that out is to take the serum test, then expose the skin to sunlight 20 minutes every day for some weeks or months, and then take a new serum test. Then you can see how much vitamin D you did get from that specific time of exposure. Perhaps it is enough, or perhaps you need to spend much more time in the sun. Or, given the dangers lurking in the radiation from the sun, you might prefer to take supplements.

Sunlight cannot cause vitamin D overdosing. UVB rays cause the production of vitamin D in your skin, while UVA tends to destroy surplus vitamin D. It keeps itself in balance.

The liver converts the vitamin to calcidiol, after that it is converted further to calcitriol, mainly in the kidneys, but also in the immune system. This is a very biologically active hormone-like substance which is responsible for most of the effects of vitamin D. (Vitamin D, or calcitriol, is sometimes classed not only as hormone-like, but as a hormone. There is some justification for this.)

Certain species of phytoplankton in the ocean synthesise vitamin D from sunlight and have done so for more than 500 million years.

Most vertebrates (and some mushrooms!) also produce vitamin D from sunlight, although for those with fur and feathers being in the way, making it impossible for sunlight to reach the skin, it is produced in the oils of the fur and feathers, then they are ingesting it through grooming. Cats and dogs, along with a few other mammals, have insufficient ability for this, and must have dietary vitamin D to satisfy their need.


Vitamin D is best known for promoting calcium absorption and to maintain a balance between calcium and phosphorus in the blood - and consequently for building up bone tissue and teeth. It is also essential for the immune system. Some studies suggest other important functions, such as protection against skin cancer. So far this is insufficiently studied, but it makes perfect sense. Why would exposure to sunlight cause production of the vitamin on the skin? The logical answer would be, to protect from sun-related damage!

In From Fungi To Cancer (e-book, 2012), I wrote:

Vitamin D deficiency has been shown to be involved in the development of a large number of diseases, for instance: Alzheimer's disease, schizophrenia, asthma, cystic fibrosis, hypertension, migraines, type 1 diabetes, rheumatoid arthritis, multiple sclerosis, even tuberculosis, and possibly autism - and, of course, cancer. It is strongly indicated in all cases of malignant melanoma. This vitamin regulates thousands of different genes. [...]

Some studies suggest that it has an ability to protect against certain other forms of cancer as well, but the results are not conclusive. The types of cancer which have been indicated are in the bladder, prostate, ovaries, rectum, and breasts.

Autism might be caused by prenatal deficiency of vitamin D, although this is not undisputed. “Prenatal” means before birth, so what we really talk about here is pregnant women and what they do or do not give their unborn child.

Male production of testosterone is dependent on vitamin D. I'm sure that many cases of decreasing testosterone levels are a result of chronic D-vitamin deficiency.

Vitamin D is involved in the ageing process. Too little as well as too much of it accelerates ageing and then it affects both physical and mental functions. The problem then is to determine the optimal dose.

Overdose of vitamin D can be dangerous and lead to an excessive calcium absorption, with deposits in tissues and organs as a consequence. This risk, however, is strongly reduced if D-vitamin is combined with vitamin K2. It is also dependent on the ratio between present calcium and magnesium. If the amount of magnesium is less than 40% of the amount of calcium, calcium becomes a potential danger. Ideally, the amount of magnesium should be 50% of the amount of calcium. So, for every 100mg calcium you take, you must also take 40-50mg magnesium. This is an often overlooked fact.

The risks with vitamin D has been exaggerated. For a long time, 400 I.U. was the recommended daily dose, and it was considered safe only up to 800 I.U. per day, at least for self-administration. Studies from the last years reveal another picture, where both need and safe dose are much higher. Indeed, the optimal dose might be as high as 10000 I.U. per day. This is not true for every individual though, so we must find a way to determine the individual's optimal dose.

Obese people need more vitamin D than others. That is because body fat binds some D-vitamin which is not released to the blood. To reach the same level in the blood, an obese individual might sometimes need twice as much vitamin D as a non-obese. But the amount is proportional to how much body fat there is.

This goes for all fat soluble vitamins. It is also to note that weight reduction can cause a release to the blood of a lot of fat soluble compounds that have been stored in the fat, including vitamins. This can dramatically increase the levels, for instance during a fast.

The danger with vitamin D is that it can lead to undesirable calcium deposits in various tissues, which can cause, for instance, cardiovascular disease. This risk is eliminated for reasonable doses by taking vitamin K2 at the same time as vitamin D. Yet everything is not known about vitamin D, one should check the level in the blood and keep it within the recommended range.


Today, official recommendations of vitamin D are around 2000 I.U. per day, and anyone can safely take that as a supplement. However, if you take more than 1000 I.U. per day, you should also take 100mcg vitamin K2. If your take more than 2500 I.U. vitamin D3, you should take 200mcg vitamin K2. That is because vitamin K2 controls how calcium is distributed in the body. It makes the calcium come in the right place (for instance bones) and prevents it from being stored in places where it can harm you (for instance arteries). Supplemental vitamin K2 is important if you take vitamin D regularly.

Warning: People who take anticoagulant medication must consult their doctor before taking extra vitamin K2! This is because some anticoagulant medicines work by vitamin K inhibition.

Vitamin D deficiency is common everywhere in the world. However, it is over the average among children, young women, people of old age, and those with dark skin. The latter is because the ability to produce vitamin D from sunlight is better, the lighter the skin is.


The best approach is to start by measuring the level of vitamin D in the blood serum. This can be done by a relatively simple blood test; a 25-hydroxivitamin D or 25(OH)D test. The result is expressed in terms of ng/ml. Less than 20ng/ml is commonly defined as deficiency. Less than 30ng/ml is sometimes called insufficiency. However, there is no absolute scientific consensus about what is an optimal level. Different sources give different values, anywhere between 30ng/ml to 80ng/ml.

I would say that less than 34ng/ml is deficiency, and that the optimal level is about 60ng/ml. That is according to the current level of knowledge.

There are two different tests. The one you want is 25(OH)D, also called 25-hydroxivitamin D. The other one is called 1,25(OH)D and it is not relevant in this context. Make sure you get the right one.

If you are serious about vitamin D, you must start by taking this test. When you know your level - which depends on numerous factors, such as your normal exposure to sun, your pigmentation, if you are obese, your diet, medicines and drugs you take, and so on - you also know if you want to increase it, which you probably want. Then comes the difficult question about how much vitamin D to take. There is no clear answer to that, because people react differently to supplemental vitamin D3. You must figure that out by trial and error. If you have anywhere less than 30ng/ml, you can start with 2000 I.U. per day. After two months of intake, make a new 25(OH)D test and compare the numbers. Then you'll see how much your serum level has increased and if you need to adjust your supplemental intake further.

Even if higher doses are required in many cases, be careful if you are going over 4000 I.U. per day – and do not under any circumstances take more than 4000 I.U. per day without taking serum tests. These tests are the only way to find out if you get sufficient vitamin D. Or by all means, if you get too much. If your test shows that you have more than 80ng/ml, you need to consider how to bring the level down.


A good vitamin D status is important for sound and healthy sleep. Indeed, a vitamin D deficiency might cause sleep disorders. That is so common that if you have any problem with your sleep, your vitamin D status is one of the first things to look at.

If you have too much vitamin D in the blood, that also causes sleep disorders. So here we have the typical pattern for vitamin D, that there is a rather narrow optimal level where both too much and too little weaken or eliminate the positive effects.

Vitamin D inversely relates to melatonin, the hormone that makes us sleep. In some cases, taking vitamin D temporarily disturbs sleep just after the intake – so it makes sense to take vitamin D supplements in the morning, not in the night or late in the day. An extra dose of vitamin D can also help you keep awake if you for some reason must not sleep.

(This article is based on material previously published in Meriondho Leo, and in my e-book “Nutrients & Dietary Supplements”, 2019.)

Related article: Testosterone: How to Keep Up the Level

Other articles related to vitamins/nutrients:

Why Dietary Supplements are Needed

Supplements, Getting Them Right: Some Points to Consider

Iron & Cancer

Co-Enzyme Q10 & Carnitine

Lutein & Zeaxanthin: Nutrients that Protect Your Eyes from Ageing

Not Only Beta-Carotene: Carotenoids (Carotenes & Xanthophylls)

Salicylic Acid: Is Aspirin a Vitamin?

Vitamin A - Function & Need

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Written by   646
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Whaoo..I can say I learn from this, I pick up the main point I needed from it .. Thanks for this

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2 months ago

hi doctor, i want to ask, what will happen if i take too much vitamin D?

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9 months ago

It leads to "hypercalcemia", an abnormal calcium level in the blood, which, in turn, can lead to a number of serious problems when surplus calcium is deposited where it should not be. The risk is lowered by a simultaneous intake of vitamin K, which, slightly simplified, controls that calcium is coming in the right places. That's why you should never take more than 1000 I.U. vitamin D without also taking vitamin K. See above

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9 months ago

thank you doctor

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9 months ago

Last year, I was suffering from chronic leg pain and Doctor scanned my legs and said it was in very bad condition but was reversable.. the ONLY solution he gave is he asked to take a lot of Vit D3, proteins and Calcium ... Protein and calcium can be achieved from food but Vit D3 is created by human body itself when we spend min 30 to 45 mins in Sunlight.. It is THAT important.... great post

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9 months ago

If your leg is so bad, I suspect you need supplemental vitamin D3, Calcium, and Magnesium. Food will hardly suffice as a source.

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9 months ago

yes yes, I'm taking those :)

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9 months ago