Posted 18 November 2016
Published in New Scientist INSIGHT 24 August 2016
TAKING a daily vitamin or mineral supplement is widely seen as a common-sense way of looking after yourself – a kind of insurance, like wearing a seat belt.
But evidence is growing that it might not be such a healthy habit after all. The latest finding is that calcium supplements, taken by many women after the menopause to strengthen bones, are linked to dementia. Among women who have had a stroke, taking calcium was associated with a seven-fold rise in the number who went on to have dementia (Neurology, doi.org/bpk3).
Although the finding came from a trial that was not randomised, and so is not the most robust type of medical evidence, the results are striking. What’s more, they come on the heels of a previous randomised trial that found a link between calcium supplements and a modestly higher risk of heart attacks. It seems caution over calcium is indeed warranted.
Team member Silke Kern at the Sahlgrenska Academy Institute of Neuroscience and Physiology in Gothenburg, Sweden, says that taking a calcium pill triggers a rapid surge in the mineral’s levels in the blood, which you don’t get from calcium in food. Such a spike could make harmful blood clots more likely to form. That could, in turn, trigger heart attacks or harm brain cells, resulting in a higher incidence of dementia, she says. If the association is confirmed, women could face a horrible dilemma: increased dementia risk versus increased risk of fatal fractures.
“Trials show that people taking antioxidants have a slightly higher death rate than those who don’t“
But there are wider lessons here. The importance of vitamins and minerals largely emerged in the last century through deficiency diseases seen in the poor. It was tempting to conclude that even well-fed individuals might benefit from taking supplements, “to be on the safe side”.
Today, about two-thirds of people in the US take a daily supplement. The adverts for such pills can be slick, often featuring celebrities testifying their benefits, but evidence of these is remarkably lacking. In the US and UK, there is, shamefully, no need for supplement-makers to carry out trials showing their products work. And as with calcium, rather than just failing to do good, some supplements may even be harmful.
For instance, many people like taking antioxidants – including the vitamins A, C and E, and the mineral selenium – in the belief that they ward off cancer by blocking damaging oxidising compounds produced by metabolism. But trials show that those taking antioxidants have a slightly higher death rate than those who don’t. The explanation for this finding is unclear. It could be because we have misunderstood how antioxidants work, or because plants contain thousands of protective chemicals, and taking a few in isolation just doesn’t have the same benefits.
In the case of calcium, it isn’t too hard to get all we need from natural sources. The UK recommended intake of 700 milligrams a day could be met by consuming, for instance, 300 millilitres of milk, a 100-gram pot of yogurt and a small 30-gram wedge of cheese.
With the exception of folic acid, which trials have shown prevents birth defects if taken before and during pregnancy, many dieticians now say that supplements are no substitute for a healthy and varied diet. There’s no better health insurance than that.