Sunlight and health - the Julian Assange conundrum

Julian Assange has now been living in the Ecuadorian Embassy for two years. He's claiming that his human rights are being breached, because not being allowed outside since he entered the embassy, for fear of being arrested, is causing him medical problems. So does he have a real case, or is this a PR stunt to gain sympathy?

There's no doubt that our mood can be affected by lack of sunlight - Seasonal Affective Disorder, or SAD, probably affects one in 50 Britons, while as many as one in eight may be prone to the milder 'winter blues'. While the precise cause isn't know, SAD appears to be caused by varying levels of brain chemicals and hormones related to sunlight. It can also run in families - if a close family member suffers from SAD, you have about a one in seven chance of being affected. Symptoms are similar to those seen in other forms of depression, although an increase in appetite and tiredness, rather than lack of appetite and feeling over-alert and on edge, are more commonly seen in SAD than in other kinds of depression.

Of course, many people who don't get outside have medical problems keeping them in bed, or have limited outdoor exposure because they're in prison. It can be difficult to work out how much of the impact on mood comes from illness or the many social problems linked to a prison sentence, and how much is directly down to lack of sunlight. However, the causal link between mood and sunshine has been reinforced by studies which have shown light treatment can be an effective treatment for many.

Then there's vitamin D, the 'sunshine vitamin'. We absorb up to 90% of our vitamin D through our skins from sun exposure between April and October in the UK, and it's hard to get enough even through the healthiest of diets. This year has been a pretty good one for sunshine, even if we have forgotten it in the aftermath of Hurricane Bertha. But while vitamin D is fat-soluble, meaning that (unlike water-soluble vitamins such as vitamin C) we can store it in our bodies and so don't need a daily dose, low levels of vitamin D are common in the UK. A consultant chemical pathologist colleague of mine, who measures vitamin D blood levels for a living, told me that in his experience low vitamin D levels are common in winter across the UK, and a major problem all year round anywhere north of Birmingham.

Along with a known link to osteoporosis, or thinning of the bones, low vitamin D levels have been accused of being a possible culprit in multiple sclerosis. The further north you live in the UK, the lower your annual sunshine exposure and the higher your risk of MS, with up to a 4-fold variation across the UK. Vitamin D deficiency has also been linked to heart disease (a consultant cardiologist colleague of mine talks about an 'epidemic' of vitamin D deficiency) and even cancer (in one scientific review, women with the lowest vitamin D levels were 50-70% more likely to get breast cancer than those with the highest levels). Very low levels of vitamin D can also cause tiredness and general aching.

The current problem we have is a lack of clear evidence that replacing vitamin D with supplements reverses these risks. However, as more and more of us cover up to avoid sun-related skin damage, it's not just people forced to stay indoors who are at high risk of vitamin D deficiency. Erring on the side of caution, the Department of Health has recommended that all under-5s, pregnant and breast- feeding women, over-65s and anyone who gets little sunlight should take a daily vitamin D supplement of 10 micrograms (400 IU).

So is Julian Assange's health at risk? He could probably do with an artificial sunlamp and a daily vitamin D supplement. Are his human rights being breached? I'm a doctor - you'd have to ask a lawyer that.

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