Vitamin D from the sun can help to protect against skin cancer, scientists say... so how long is OK to spend in the sun?
When Paul Banwell, a consultant plastic surgeon and skin cancer specialist, was doing his fellowship in Australia over 10 years ago, he discovered a peculiar fact: virtually all the dermatologists he was working alongside in Sydney and Brisbane were vitamin D deficient. One even had a pathological fracture (a bone fracture caused by weak bones).
"They cover up in the sun the whole time over there, both with clothes and sun cream," explains Banwell. "As a skin cancer expert myself, I tell patients to wear sunscreen every day, but in Australia, they take the sun safety message to the extreme and they're lacking in vitamin D as a result."
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This anecdote may go some way to explaining the increasing levels of vitamin D deficiency worldwide. The sun safety message - which started with Australia's 1981 'Slip! Slop! Slap!' public health campaign to reverse the country's soaring rates of skin cancer - was so well absorbed around the world that people's concern about protecting themselves from the sun meant they overlooked its health benefits. Namely, how it helps the body produce vitamin D.
Yet this week, a slew of studies presented at the American Society of Clinical Oncology annual conference in Chicago found that vitamin D - from both sunshine and supplements - could reduce your risk of dying from several types of cancer.
The experts at the conference couldn't say why, but suggested vitamin D may enhance the body's immune response, and Dr Tarek Haykal, a lead researcher from Michigan State University, urged GPs to recommend supplements.
"We now know that good levels of vitamin D are linked with a reduced risk of a variety of different cancers," says Banwell. "At last count, it was 15 types, with the main ones being colon, prostate, breast and skin. It's a bizarre paradox that vitamin D from the sun actually helps to protect against skin cancer. It seems to be protective on a cellular level."
The Chicago conference referenced studies that found those told to take vitamin D supplements were no less likely to get cancer, but were 13pc less likely to die from the disease. Supplements were linked to a 38pc drop in prostate cancer deaths, while the link with pancreatic cancer was also strong - being deficient in vitamin D can double your risk of developing it.
"Vitamin D is a fat-soluble vitamin stored in the body," explains dietitian Helen Bond. "The sun is by far the best source, but you can also get it from food and supplements. For years, we've known vitamin D maintains healthy bones. But in recent years, there has been a lot of new and exciting research suggesting it can help protect against certain cancers, Type 1 diabetes, cardiovascular disease, age-related macular degeneration, mental decline, multiple sclerosis and rheumatoid arthritis."
Another study has found it can increase fertility in both men and women, improve the chances of IVF success, and help regulate menstrual cycles in women suffering from PCOS (polycystic ovary syndrome). Yet it's thought one in four adults here are vitamin D deficient.
So just how much do we need? The Food Safety Authority and the Health Service Executive recommend that all babies 0 to 12 months should receive a vitamin D supplement.V itamin D3 is the preferred form of the supplement for infants.
In the UK, the NHS recommends that children from the age of one need 10 micrograms of vitamin D a day, and recommends that breastfed babies be given a daily supplement of 8.5 to 10 micrograms of vitamin D each day (formula fed babies don't need it, as formula milk is fortified with vitamin D), and children aged one to four be given a daily supplement containing 10 micrograms.
Adults should take the same amount from October through to the end of March - from then until the end of September, most people should get all the vitamin D they need from sunlight on their skin. "Fifteen minutes of unprotected sun exposure every day is sufficient, and comes with a psychological benefit too," says Barnwell.
The main take away from these new studies, says Banwell, "is to take a 5:2 approach to vitamin D - five parts good quality supplements and two parts moderate, modest sun exposure. Along with a good vitamin-rich diet, this will ensure you get just the right amount to stay healthy all year".