D is for…

Vitamin D, pretty in the sun

Vitamin D, pretty in the sun by Perfecto Insecto, on Flickr

The sun’s been shining a lot recently, but do we get all the vitamin D that we need from natural light? And what good does the vitamin do us anyway? Benjamin Thompson spent his lunchtime indoors finding out…

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On a beautifully sunny spring day this April I sat in Wellcome Collection listening to an excellent talk about vitamin D, ‘the sunshine vitamin’ (oh, the irony). The speaker was Dr Adrian Martineau, Senior Lecturer in Respiratory Infection and Immunity at Barts and The London Medical School. He spoke about the ways in which vitamin D is made and how it may have many unexpected health benefits.

Dr Martineau trained as a doctor in Newcastle and Liverpool and spent time working in a rural hospital in South Africa. Given the high prevalence of HIV in South Africa, there are also high levels of TB (find out more about TB and World TB Day on the Wellcome Trust blog).

On his return he became interested in an article written by his future PhD supervisor detailing how patients with latent (dormant) TB infections have a higher level of vitamin D in their bloodstream than those with active TB.

Dr Martineau’s PhD involved a randomised study to determine whether it was the TB that made patients vitamin D deficient, or if having a low level of the vitamin increases the risk of developing TB. The results showed that in fact, a higher level of vitamin D in the blood enhanced the ability of the immune system to fight the infection.

The talk was not just about bacterial infection, with Martineau explaining much about how vitamin D is made and why we need it.

The major source of the vitamin is made in a chemical reaction in the skin in response to UVB light from the sun. This light causes a chemical reaction to occur, converting (wait for it) 7-dehydroxycholesterol into 1,25-Dihydroxyvitamin D.

When sunlight is weak, such as in the UK in autumn and winter, we can’t make any vitamin D so need to get it from the food we eat – particularly oily fish. However, to entirely supplement our diet in this way we’d need to eat fish three or four times a day, which is simply not possible. This means that most of us during the colder months have sub-optimal levels.

The childhood disease rickets is caused by severe vitamin D deficiency, and the role the vitamin plays in the absorption of calcium and hardening of bone is well understood. Less well understood is why else it may be important. Over the past 20 years it has been discovered that a wide variety of cells, not just those in the skin, can make vitamin D – with an equally diverse number of cells having chemical receptors to accept the molecule. This is an indicator that the vitamin is important and affects many parts of the body.

Population studies have shown that those with lower vitamin D levels tend to have higher incidences of a number of diseases, including diabetes and cancer. However, given that it can be linked to so many diseases, are these low levels the cause of the problem, or are other factors such as an unhealthy lifestyle to blame?

As many of us in the UK appear to have low levels of vitamin D in our blood, Dr Martineau suggested it was time that nationwide food fortification or dietary supplementation are investigated. Will raising the overall levels of the vitamin improve the nation’s health? Some foods, like breakfast cereals, are already fortified, and studies in other countries have shown that it is a safe practice. Thankfully it’s very difficult to take an overdose by mistake, with the body able to break down any excess when present.

The speaker himself explained that he takes vitamin D pills to supplement his diet. We also learned how these pills are made. It turns out that the most common form (vitamin D3) we can buy is made from sheep’s wool. The molecule lanolin from the wool is extracted and exposed to UV light to make the vitamin D.

With the weather getting better, and learning all I did from this Packed Lunch, I can’t wait to get outside and top my vitamin D levels up (sensibly, of course – getting burnt is dangerous). It’s certainly given me something to think about over the winter months too.

Benjamin Thompson is a writer at the Wellcome Trust.

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