If you want to start a row at a social gathering of doctors, just ask them about the benefits of taking vitamins. Typical of the current debate was a recent editorial in the Annals of Internal Medicine that advised “stop wasting your money” on vitamins. The journal concluded that there is “no clear evidence of a beneficial effect of supplements on all-cause mortality, cardiovascular disease, or cancer”.

That seems clear, but for virtually every detractor of vitamin supplements there are legion supporters. Some may be companies that sell vitamins and so their motives are a tad suspect. But there are also plenty of researchers who have found genuine benefits. Whom to believe? Let’s look at just one controversial supplement, vitamin D, which is in fact a hormone.

In the past century, researchers have noticed that people who live in the southern part of the US tend to have fewer serious illnesses than those in the north, especially in the winter. This led to speculation that vitamin D, synthesised in the body from sunshine, might help stave off disease.

Since then there have been hundreds of studies saying that vitamin D has a role in preventing illness. Once thought to be beneficial only to bones, it is now known to have far-reaching effects in the body. After much deliberation, the prestigious US Institute of Medicine has even set a recommended daily intake of 600 international units (IU) for most adults.

However, that has not stopped doctors casting doubt on vitamin D’s effectiveness, as two studies published in the British Medical Journal in April attest.

One of the most debated studies about vitamin D ever conducted was undertaken by Joan Lappe, a professor of endocrinology at Creighton University medical school in the US state of Nebraska.

Prof Lappe did an interventional study using supplements of vitamin D and calcium (she was originally looking at preventing osteoporosis) with 1,100 women over the age of 60 in Nebraska. The results were fairly dramatic: if you exclude the first year, in which cancers were presumably already present but not yet diagnosed, there was a 77 per cent risk reduction in those taking vitamin D.

“It was really a breakthrough because it was the first time we’ve seen that vitamin D can make a difference in the incidence of cancer,” Prof Lappe says. But since the researchers were originally looking for osteoporosis fractures instead of cancers, the study was criticised.

Prof Lappe and her mentor, Robert Heaney, have written a thought-provoking explanation of why some previous randomised controlled trials of vitamin D found no benefit. In short, taking vitamins may be a little like pressing a doorbell: if you press a little, nothing happens, but when you press harder the bell rings. So studies using 400IU of vitamin D may show no effect, while those using 1,100IU, as Prof Lappe did, show benefit.

The purpose of this column is not to debate the validity of a scientific study but to make health suggestions to busy executives. While the efficacy of vitamin D is still being studied, Prof Lappe and others recommend most people take 2,000IU a day and have their vitamin D levels checked. Taking that quantity of vitamin D3 (much preferred over vitamin D2 because it is more easily converted to the biologically active form of the vitamin) has no real down side: there are no known side-effects and it could improve resistance to colds and serious illness.

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