08 February 2016 17:04:19

Julian Assange and the vitamin D debate

You might have thought that this week's news that the United Nations has declared that Julian Assange is being 'arbitrarily detained' in the UK wasn't of any professional interest to a doctor. But my phone kept buzzing with media requests to talk about the health implications of lack of sunlight. Assange has, after all, spent over 3½ years cooped up in the Ecuadorian embassy in London.

Now I'm not a politician, and I'm here to talk about health, so I shall keep my views on his reasons for refusing to come out to myself. But it did give me an opportunity to think about how long periods inside can damage our health.

Top of the list is vitamin D. The vast majority of the vitamin D in our bodies doesn't come from what we eat, but is made in our skin when it's exposed to sunlight. In recent years, there has been more and more awareness of the risk of low vitamin D levels because of a combination of increased awareness of the risk of skin cancer from excess sun and more of us spending all our time indoors at work.

Most of our knowledge about vitamin D has come in the last few years, and there are still an awful lot of question marks. There are various guidelines for 'ideal', 'insufficient' and 'deficient levels, but confusingly different laboratories use different ways of measuring vitamin D. For instance, my local lab defined 'ideal' levels as over 70 nmol/l, insufficient as 40-69 and deficient as under 40. In other parts of the country, the equivalent figures might be over 50, 25-49 and under 25 respectively.

We don't really know how much sunshine is needed to get enough vitamin D. For six months of the year, sunshine in most of the UK isn't strong enough to allow us to manufacture vitamin D from cholesterol in our skins. Vitamin D is 'fat-soluble' - meaning that unlike water-soluble vitamins like vitamin C, we can store it in our bodies and don't need to have it every day. So guidance varies from 20-30 minutes three times a week to 15 minutes a day, between April and October, in sunshine, with face and arms uncovered and no sunscreen.

We have long known that low levels of vitamin D are associated with a higher risk of osteoporosis and rickets in children. More recently, low levels have been linked to higher levels of heart diseasedepressionmultiple sclerosis and even cancer. The trouble is, we're not absolutely certain if it's low vitamin D that's actually causing these problems or if there's a 'confounding factor' causing it.

Let me give you an example. A few decades ago, a study showed higher levels of lung cancer among coffee drinkers. Was the coffee causing the cancer? In this case, the 'confounding factor' was smoking - heavy coffee drinkers were more likely to be smokers, and it turned out that once you took the smoking out of the equation, the link disappeared.

We also aren't certain if replacing vitamin D with supplements, rather than sunshine, protects against these conditions. However, there's enough concern about low vitamin D for the National Institute for Health and Care Excellence (NICE), to recommend supplements of 10 micrograms a day, for:

- Infants and children aged under 5

- Pregnant and breast-feeding women, particularly teenagers and young women

- People over 65

- People who have low or no exposure to the sun - for example, those who cover their skin for cultural reasons, who are housebound or confined indoors for long periods

- People with darker skin - for example, people of African, African-Caribbean or South Asian family origin.

There's certainly an awful lot of low vitamin D about. In the last few years, since I've been checking vitamin D levels among my patients, I've more often seen low levels than normal. So if Julian Assange is short of vitamin D, he's in good company. And while I can't give him a guarantee that a simple supplement a day would solve all his problems, it's certainly worth a try.

Dr Sarah is unable to provide medical advice or respond directly to questions concerning your health. If you have health concerns we recommend contacting your GP.