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Tuesday, February 19, 2013

Dietary supplements ~ useless or useful?

There is a general tenet in human nutrition that if one eats a healthy diet, then there is no incremental benefit from taking additional nutrients either as fortified food or as supplements. A healthy diet should provide all of one’s nutrient requirements. I would go so far as to say that, among nutritionists, this is more a doctrine than a mere tenet. In recent times, several papers have been published which challenge this concept. A good place to start is with a major survey of 12,000 US adults to ascertain and characterise usage of dietary supplements[1]. In 2011, Americans spent $30 billion on dietary supplements, which, to put it into perspective is equal to or greater than the annual GDP of Ethiopia, Jordan or Bolivia. Some 77% of the users of dietary supplements do so through their own choice with 23% doing so on professional advice. In general, users of supplements are happier with their health than non-users, which suggests that they use supplements as some sort of insurance. The vast majority of respondents stated that they took supplements to “improve” or “maintain” health. So, are they wasting their money?  A recent meta-analysis would say that indeed they are wasting their money where the end point was mortality. In this study, the authors completed a meta-analysis of dietary supplement (multi-minerals and multi-vitamins) intervention studies, which involved a final list of 21 publications, involving 91,074 adults, with a mean age of 62 and a mean duration of supplement use of 43 months. A total of 8,794 deaths was recorded. When the death rate of those assigned to intervention with the supplements was compared to that of those receiving a placebo, no statistically significant differences in death rate were seen. So, taking dietary supplements doesn’t make you live longer. But do they make you healthier?
Late in 2012, two papers were published from the “Physicians’ Health Study II Randomized Controlled Trial”. This began in 1997 with 14,641 male physicians aged 50 years or greater entering the study. There were several treatments. One involved a multi-vitamin supplement. Two others involved either vitamin E alone or vitamin C alone. A final group received a placebo. After an average follow up of 11.2 years, 1,732 cases of major cardiovascular events (non-fatal serious heart attack or stroke) were observed[2]. No statistically significant differences were observed in cardiovascular events between treatment and placebo. So supplements wont make you live longer and wont make your heart any healthier. However, a second paper from the same Physicians Health Study Randomized Controlled trial did show that the overall risk of cancer was moderately reduced in those assigned to the vitamin supplements as opposed to those assigned to the placebo[3]. The authors conclude that: “Although the main reason to take multivitamins is to prevent nutritional deficiencies, these data provide support for the potential use of multivitamin supplements in the prevention of cancer in middle-aged and older men.” What a pity these studies didn’t employ modern genomics and metabolomics technology to look at responders and non-responders. When will nutritional epidemiology enter the 21st century?

The issue of vitamin supplementation was the subject of yet another recent paper, this time with a focus on folic acid supplementation in the pre-natal period and during pregnancy. Normally the end-point of such interventions would be neural tube defects such as spina bifida but in this case it was autism. The study was within the Norwegian Mother and Child Cohort study, which recorded the use of folic acid prior to conception and in the first 8 weeks of pregnancy[4]. Among the 85,176 children born in the cohort after exclusion of some births (12,000) for reasons such as premature delivery or lack of data on folic acid use, some 114 cases of autism were observed, equating to a rate of 0.14%. Among women who took folic acid supplements the rate was 0.10% while among women who didn’t take folic acid supplements the rate was 0.21%. This difference was statistically significant even when controlled for maternal and paternal education and age, a planned pregnancy, parity, year of birth and maternal BMI and smoking habits.
Clearly, some people benefit from dietary supplement use and the challenge to nutritional science must be to use modern technologies to ascertain those that do and don’t benefit with a view to customizing supplement use to optimise health. The doctrine that states that you should get all your nutrients from foodstuffs is codswallop.

[1] Bailey RL et al (2013) JAMA Int Med, On line February 4th
[2] Sesso et al (2012) JAMA, 308, 1751
[3] Gaziano JM et al (2012) JAMA, 308, 2012
[4] Suren P et al (2013) JAMA, 309, 570

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