There has been a lot of talk about vitamin D in the news – and the talk is all about cancer. A large study from Nebraska recently found that women who took vitamin D for four years got 77% fewer cancers. This could point to a huge potential problem, since up to 97% of Canadians do not get enough vitamin D for at least part of the year. That may be the tip of the iceberg, since cancer is not the only problem with lack of sunshine.

During hundreds of million of years of evolution, Homo sapiens spent most of our waking hours under the hot African sun – and now we are lucky if we get to spend ten minutes in the sun over lunch. Clearly this is dramatic change in our environment affects us – and vitamin D is the first example. We hear more about the sun’s risks than its benefits, but researchers estimate that for every skin cancer is prevented, avoiding the sun may cause a hundred more.

Vitamin D is not really a vitamin – it is a hormone. It acts like a switch in many different cells of the body, turning on or off the complex DNA systems that make enzymes and other important machinery. For many years, it was believed that it was most important for bones, but current research is more focused on its role in regulating the immune system and other bodily functions. This explains the strong link between vitamin D and many diseases of the immune system – including multiple sclerosis, asthma, allergies and type 1 diabetes. Research suggests that vitamin D supplements may decrease the risk of these illnesses – by up 80-90% in most studies. If you suffer from any illness linked to the immune system, vitamin D may be especially important for you.

Another hugely important link is that between vitamin D and the nervous and musculoskeletal system. It is well-known that it is important for healthy bones and prevents fractures in people with osteoporosis. Newer research suggests that treating vitamin D deficiency can prevent falls in the elderly, eliminate chronic back pain, and may even improve some of the symptoms of fibromyalgia. The findings are so dramatic that the medical definition of normal blood levels of vitamin D has been raised. The old range – based on preventing a now-rare disease called rickets – has been almost doubled. In truth, ideal blood levels are not yet known but a minimum of 100 nM (nanomoles per litre, for those of you who care) is advisable. Based on recommendations from international expers, we aim for 120 nM in our patients.

What’s more, the Recommended Daily Intake of vitamin D has just been raised from 400 units to 800 units per day. Although I normally recommend that patients get their vitamins from diet instead of supplements, there is not much vitamin D in food. Although a 4oz serving of wild salmon might have 1000 units, farmed salmon has much less. Foods that are fortified with vitamin D provide too little. Cod liver oil is rich in vitamin D – and omega-3 fatty acids – but it has too much vitamin A to be used widely.

The only truly natural way to get vitamin D is the sun. If you are fair-skinned, fifteen minutes of bright midday summer sun on your arms and face will produce 400 units of vitamin D. Darker-skinned people may take four times as long to get the same result. Some researchers recommend tanning beds as a means of getting vitamin D but most feel that a daily supplement is safer.

In the Nebraska study, all the women got the same amount of vitamin D – around 1200 units. Some people need this much, others may need more. Ideally, your doctor should measure your blood levels of 25-OH vitamin D – the storage form – to decide how much you need. There is very little risk of taking too much vitamin D – toxicity has only been noted after long-term use of 10-15,000 IU.

When patients are admitted to hospital, they rapidly lose muscle and are at risk of infection. This has been blamed on bedrest, but could lack of sunlight be a factor? We accept that flu season comes in the fall, but research suggests it may all be vitamin D.

An Iranian population study found vitamin D deficiency in 18% of men but 72% of women. Will Islamic women continue to cover their skin as per tradition when they find out it increases their risk of cancer and autoimmune disease in their children?

It is difficult to overstate the potential importance of this discovery. Vitamin D may be the biggest medical news since antibiotics. If it has even one tenth of the effect that current research suggests it does, some fun in the sun – or at least a vitamin D supplement – might be just what the doctor ordered.