Tuesday, January 14, 2014

Multivitamin supplements

Give a talk on any aspect of nutrition and there is a good chance that you will be asked “Should I take a vitamin supplement?” A realistic answer would be: “If you are here at a presentation on nutrition, then there is a good chance that you eat well and are least likely to need any supplement.” But that’s not what people want to hear, because a supplement is seen as taking control of your own health.

Literature review
A review of all the literature published from 2005-2012 on vitamin and mineral supplements has looked at their ability to influence heart disease and cancer, either of which conditions are likely to be on your death certificate if you live a long and fruitful life, remembering that you can’t die of birthdays, wisdom and experience (formerly known as old age). They looked at virtually all the vitamins, along with the minerals calcium, iron, magnesium and selenium.
  
No effect on heart disease
Multivitamins don’t appear to have any effect on the risk of heart disease, although there might be a slightly lower risk of cancer but that was a borderline result. However, there was no overall effect on mortality from all causes over the period of each study. Even when looking at combinations of nutrients the results were very inconsistent. One selenium study showed a lower risk of cancer while another didn’t, and as there were only two good studies on selenium, which result do you want to believe?

Beta-carotene kills smokers quicker
Six trials on beta-carotene showed no effect on the risk of heart disease or cancer, unless you are a smoker or asbestos worker, then beta-carotene supplements increase your risk of lung cancer. This result has received lots of attention in the past as it appears that beta-carotene accelerates the proliferation of existing lung cancer cells.

What might be better than a multivitamin?
This is not the first review that has concluded that there is no consistent evidence that vitamin and mineral supplements do not lower the risk of cancer or heart disease, nor reduces the risk of early death. It follows at least 10 others, including some on antioxidant supplements, with the same conclusion. Thankfully, there was no evidence of harm either.

The authors state that one reason for the disappointing effect of multivitamins might be that: “physiologic systems affected by vitamins and other antioxidant supplements are so complex that the effects of supplementing with only 1 or 2 components is generally ineffective or actually does harm.”

My biased take on this is that there may be a lot more than vitamins and minerals helping to reduce disease risk, like the many thousands of other bioactive compounds found in food, so eat good quality food. Well, someone had to say it.

Of course supplements do have their place, such as folate taken before and during pregnancy to lower the risk of having a child with spinal deformities.

What does it all mean?
These studies were done in people who were otherwise well, in other words they may not have got the kind of benefit from a supplement as someone who was sick, ate poorly or sleeping under a bridge each night. So, the studies didn’t include people who were nutrient deficient (eg iron deficiency anaemia) who would clearly benefit from a suitable supplement.

Virtually all the studies were run over 10 years or less, and very few included women. As you know, studying humans is expensive so we rarely see studies over 3-4 decades. Maybe there is a long-term benefit for taking supplements over half a century, who knows?

Whether you should take a multivitamin supplement or not is your choice. Just don’t expect too much from them, certainly not the benefits you will get from eating well, being fit, hugging the kids, donating to charity, reading a good book and (insert your favourite safe, inexpensive, endorphin-liberating and legal past-time here).


Reference:

Fortmann SP et al. Annals of Internal Medicine 2013; 159 (12): 824-834

3 comments:

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