When it comes to healthy living, none of us are perfect. That's why Canadians spend nearly $3-billion a year on vitamin pills and other dietary supplements, in the hope that they can function as a form of insurance against dietary and lifestyle lapses. Here are three reasons to reconsider that strategy:
They may not work
The debate about vitamin pills has never been too concerned about evidence. If it was, there would have been more hubbub surrounding last month's scientific review by the non-profit Cochrane Collaboration.
The review combined the results of 78 randomized trials – the strongest form of medical evidence available – in which 297,000 people were assigned to take an antioxidant pill, a placebo, or nothing. The analysis showed no benefit from vitamins A, C, and E, selenium or beta-carotene, either for healthy or sick people; in fact, those assigned to take the vitamins were slightly more likely to die during the follow-up period.
The findings are hardly new – they merely confirm earlier studies. Similar doubts plague most supplements, with the highest-quality studies least likely to find benefits.
It's not the micronutrients that are the problem; it's the form they come in, says Jeff Coombes, an antioxidant researcher at the University of Queensland in Australia.
"Food derived from an animal or plant origin is constructed over millions of years to be in quantities where the nutrients work synergistically together," he says. "So thinking you can take the nutrients out of that package and get similar benefits is a big stretch."
They might harm you
Many vitamin users reason that vitamin pills can't hurt you, and that it's still worth taking them just in case the benefits turn out to be real.
The problem is that evidence increasingly suggests that they actually can hurt you, Dr. Coombes says. The strongest evidence comes from a major randomized trial of 35,000 men, published last year in the Journal of the American Medical Association, that found a significant increase in prostate cancer among the subjects assigned to take vitamin E.
And although they are less reliable, many observational trials have linked common supplements – including multivitamins, folic acid, iron, zinc, calcium, carotenoids and vitamin B6 – to outcomes such as increased recurrence of breast cancer and premature death.
Of course, there are also observational trials that report positive outcomes from vitamin use. But the links between diet, environment, genetics and health are too convoluted to say with confidence which findings are robust and which are the result of hidden biases like the "Girl Scout effect" (the clustering of "healthy" behaviours in certain people that makes it almost impossible to tease out the key factors in observational studies).
The point remains: Any given pill may have benefits, and it may have harms. But it amounts to micro-nutritional roulette, not harmless insurance.
They make you feel (falsely) invincible
Psychologists at National Sun Yat-Sen University in Taiwan have performed a series of fascinating studies on the "licensing effect," showing how we inadvertently change our behaviour – for the worse – after doing something we believe is good for us, like taking a vitamin pill.
The researchers asked volunteers to complete a series of tests whose true purpose was disguised. In one of the tests, they were asked to assess the shape and texture of a pill; half the subjects were told it was a multivitamin, while the other half were told it was a placebo (in reality, all the pills were placebos).
In subsequent tests, the subjects who believed they'd taken a multivitamin repeatedly behaved in less healthy ways. When they were asked to test out a pedometer by walking either a long or short route, the vitamin group was more likely to choose the short route. When they were given a coupon for either a "healthful, organic meal" or a less healthy buffet lunch, the vitamin group was more likely to pick the buffet.
Psychological tests revealed that the simple act of taking a vitamin pill made the subjects more likely to agree with statements like "Nothing can harm me," and more likely to express desire for "hedonic activities that involve instant gratification but pose long-term health hazards (e.g. casual sex, sunbathing, wild parties)."
Of course, the licensing effect doesn't just apply to pills. You're also more likely to indulge yourself after going for a run. The key difference is the run really did boost your health, so you still wind up ahead.
So what should you do?
Vitamins first made their reputation as a defence against diseases of deficiency – vitamin C against scurvy, for example. In those situations, they really do work. So there's an undeniable logic to the idea of taking a pill to top up any nutrients that your diet may be short on.
But the pills also help to create the very deficits they're supposed to fight, subtly licensing us to opt out of the extra effort of packing an apple, peeling a carrot or heading to the gym.
This doesn't mean you need to banish all pills from your home. But consider the reasons for taking each one, and the strength of the evidence, and ask whether they're addressing a real need in your current life or merely insuring against a hypothetical one.
For my own situation, the only pill that reaches that threshold right now is vitamin D. The evidence isn't definitive, but it's enough. Besides, I need something to make me feel invincible in the morning.
Alex Hutchinson blogs about research on exercise at sweat-science.com. His latest book is Which Comes First, Cardio or Weights?