Vitamin D

All of the following is from my reading of various sources, the most useful being Medscape. I am not a medical expert so please do not take these as my recommendations.

There is a growing body of good scientific evidence that many, or most, of us suffer from vitamin D deficiency, especially in winter. We have adopted an Australian obsession with the danger of sunlight, even though we get little sun compared with Oz. Obviously we should not risk skin cancer by getting badly burned or lying in the sun for days. However many people now plaster themselves, and even worse their children, with sunscreen. Factor 15 blocks 98% of the ultraviolet that is essential to provide us with vitamin D. I watch with dismay as parents slather sunblock on their pale children. People with dark skin are particularly at risk and doctors are starting to see children with rickets.

Correlation is not causation. Science, unlike other areas of human thought like religion and politics, insists that any idea must be capable of being tested and must be abandoned if shown probably to be false. There appears little doubt about the need for vitamin D to ensure bone health. However some scientists suggest that the low vitamin D levels found in people suffering from other diseases might be the result of the disease rather than its cause. This will only be decided as further studies generate more data.

Bearing all that in mind, if, like me, you read Medscape you will have read a series of studies that appear to show that vitamin D is essential to us and that proper levels of it in our blood protect us against, or help to cure, a variety of diseases. Several recent summaries list a wide range including bone, cardio-vascular, nerve, mental problems and some cancers. They also mention lung disorders like tuberculosis. At one time the only cure for TB was all-day exposure to sunlight in the mountains. Now we know why.

Vitamin D supplements are cheap and cause no harm, so if they only help with some of the diseases discussed later, they are worth taking. Of course sunlight on the skin produces vitamin D. However the suggested daily exposure is about 20 minutes on a quarter of the body area at mid- day in summer. Being realistic, few people will be doing this, especially in the winter, and even in summer the fashion is for avoiding the sun.

A summary Medscape article on 12th February 2013 listed references to fifty-one studies. If you want to read it please click here. I can't promise that the links in it will work for ever.

To read the article of 5th August 2014 click here.

A further Medscape article in August 2014 is a large and thorough summary aimed at doctors but nevertheless well worth reading. Click here to download.

There is now a California-based organisation set up to disseminate data about vitamin D and health. It asserts, "The Vitamin D Council is a 501(c)(3) nonprofit organization, working to educate the public on vitamin D, sun exposure and health." I don't know if it is truly independent and scientific but it seems well worth a look at

Why are we deficient?

A New York Times article in December 2015 describes DNA analysis done by David Reich and others at Harvard Medical School on dozens of samples of ancient DNA that suggests that it was not the move to less sunny climes that caused European skin to lighten. Rather it was the arrival of agriculture. A diet high in grains and vegetables and low in animal foods is very low in vitamin D. So natural selection lightened our skins to get more D from the sun. If we avoid the sun, or there is none, we are likely to be deficient.

How much do we need?

In talking about doses, an earlier Medscape article states, "Only a few foods are a good source of vitamin D. These include fortified dairy products and breakfast cereals, fatty fish, beef liver, and egg yolks." The only true way to find out if we are deficient is by a blood test. However the preferred variant, vitamin D3, is now shown not be toxic at high doses as was once believed. Though D is present in fish oils, the article warns against taking high doses of these, as you will probably get vitamin A poisoning.

Supplements are cheap and are recommended in the article. A typical multivitamin pill will contain 5 micrograms (ug) of D3, which is 200 international units (IU). A higher dose vitamin D3 one will have 10 ug (400 IU) or 25 ug (1000 IU). If you don't have your blood tested then you can go by the US Recommended Dietary Allowance of 600 IU for people aged 1 to 70 years and 800 IU for those who are older. Some suggest 1000 IU a day. Others say 5000 and pills of this strength are now available. Very high single 'bolus' doses of 500000 IU were used in some trials.

The article warns about possible drug interactions so you might need to tell your doctor if you are using it and taking other drugs. Vitamin D is not actually a vitamin. You can learn about it in the Wikipedia article. It is only soluble in fat so must be taken with, or shortly before or after, food.

A study reported in December 2015 by the Vitamin D Council suggests that it is important to take D supplements daily, not in large bolus doses weekly or monthly. D is probably not stored as was believed. This might be the reason why studies that use bolus doses find negative results for the benefits of D.

A trivial but interesting fact is that in Holland vitamin D is made from the lanolin oil on sheep's wool. It is blasted with intense light and the D is then crystallised. A kilogram is worth £250 000.

Medscape on 20th August 2014 published a paper by Dr C F Garland, a world expert on Vitamin D. He concludes that most people are D deficient. He applauds Barack Obama's doctors for diagnosing this and putting him on supplements. His study concentrates on cancers particularly bowel. He notes that this is almost non-existent near the equator and rises steadily towards the poles. He shows that increasing levels of blood vitamin D result in reducing levels of disease. The current danger level of 20 ng/ml is far too low. This should be at least 30 and two-thirds of the US population is probably below this. Higher levels are better though he notes some studies state that 70 might be too much. He thinks that people should take 2000 IU a day which is 50mg. Up to now 1000 was regarded as a high dose. Others suggest 4000 to 5000. He thinks everyone should be tested in March each year when levels are lowest. The paper is well worth a read.


(C) Peter Scott 2013

Last edit 8 March 2019