Back in 2007, a controversial meta-analysis published in the Journal of the American Medical Association linked antioxidant supplements to all-cause mortality. The study repurposed data from 68 randomized clinical trials with 232,606 participants, and found a 16% increase in mortality risk from supplement intake of popular antioxidants such as vitamins A, C and E, and beta-carotene. This initial study was conducted by Goran Bjelakovic of the Copenhagen University Hospital.
In a recent re-analysis of the original meta-analysis, Hans Biesalski of the University of Honheim led a team of scientists to different result. In looking at the same data set, Biesalski found:
36% of the trials showed beneficial outcomes to antioxidant supplementation
60% showed null outcomes
- 4% showed negative outcomes
The scientists, in reporting their results in Nutrients, found benefits correlated to vitamins C and E, selenium, beta-carotene and zinc. Supplementation appeared to be most effective in treating and preventing chronic health conditions when the user had inadequate levels of these micronutrients from diet alone, but nothing as severe as an overt deficiency. The scientists went on to suggest that thresholds do exist beyond which additional supplementation provides no further benefit.
NBJ Bottom Line
We've seen these meta-analyses wreak havoc in the past. One such study from 2005 linked vitamin E to all-cause mortality, and vitamin E supplement sales dropped 32% in a year. Those sales have yet to fully recover.
Just last month, another meta-analysis linked calcium supplementation to heart attack risk. National media picked up the story and reported it broadly, so we'll have to see what effect, if any, this carries into future calcium sales.
In the interim, as we wait for evidence of a boost to antioxidant sales in the ping-pong match of secondary clinical analyses, a larger point can be drawn. In a statement to Nutraingredients.com, Andrew Shao, PhD, Senior VP of Scientific and Regulatory Affairs for the Council of Responsible Nutrition, said: "Rather than simply examining numbers to see if the risk for total mortality is increased, this group of experts examined the same studies to (a) see if there was any statistically significant benefits demonstrated and (b) if the effects were biologically plausible. Aside from all the weaknesses and limitations from the previous meta-analysis, these are important questions that were never considered by Bjelakovic. Not surprisingly, they reach a different conclusion."
Experts will continue to question the relevance of meta-analysis, but perhaps a more balanced approach to its practice, one that seeks out benefits as well as risks, might go some measure to ease industry's concerns. In this day and age, we need plenty of good news to temper the bad.
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