The balance between Vitamin D production and Skin Cancer prevention
Hannah: - Well apart from food, a major source of vitamin D is exposure to sunlight which makes the hormone in the skin. So, some sun is good but therein lies the rub because sunlight can also cause skin cancer. Well to find out what's best, we've asked our own Dr. Kat Arney from Cancer Research UK to take a look at the evidence.
Kat: - Despite what some people claim about the cancer-preventive properties of vitamin D, in reality the scientific evidence is much more confused. For a start, most of the studies that have looked at the links between vitamin D and cancer suffer from poor methodology - meaning that their methods aren't sufficiently rigorous to draw any strong conclusion. For example, most studies are what we call "ecological" - they look at how rates of different cancers change depending on where in the world you live, and find that the further north from the equator you go, the more likely people are to develop, or die from, many types of cancer.
The big idea is that the sun's rays are weaker at higher latitudes, so people living in northerly places make less vitamin D. And it's this that, in theory, accounts for their higher rates of cancer. But in fact it's really hard to tell what anyone's individual vitamin D level is based just on where they live. Everyone's skin is different and makes different amounts of vitamin D with the same sun exposure.
These studies also tend not to adjust for other things that could explain the differences, such as what people eat, how active they are or how wealthy they are, and their behaviour such as tanning, taking sunny holidays, or working outside. All these things have a much greater effect on a person's vitamin D levels than simple geography does.
In terms of vitamin D preventing cancer, the strongest evidence is for bowel cancer. It seems that low vitamin D is associated with higher bowel cancer risk, but it's not clear whether the vitamin is actually preventing the disease, or whether it's representing another aspect of health. And the evidence for a role for vitamin D in other types of cancer varies from non-existent to limited. Trials testing whether vitamin D supplements can reduce the risk of cancer haven't shown an effect, but they've also had problems with the way the studies were done.
So what do we know? It's clear that we all need a bit of sunshine in our lives, and that vitamin D is important for general health but when it comes to cancer risk there's one long-known and very strong association between UV light from the sun and sunbeds - and that's skin cancer. Excessive UV exposure - particularly getting sunburnt - significantly increases the risk of skin cancer, including malignant melanoma, the most dangerous form of skin cancer.
For most people it should be possible to strike a balance between making enough vitamin D and not raising the risk of skin cancer, although how much vitamin D you can make through your skin depends on your skin type, and your behaviour - such as whether you stay in the house all the time, or wear thick clothing that covers your whole body. But it's important to remember that the time in the sun needed to make enough vitamin D is usually short, and less than the amount of time it takes the skin to redden or burn.
So there's no need to roast yourself to a lobster-like shade of red in an attempt to boost your vitamin D, as it won't help - and not only will you be increasing your risk of cancer, you'll also be helping your skin along the way to that lovely leather-handbag look."