New data on supplement use reveal changing habits since 1999.
In 2002, a high-quality randomised trial published in the journal JAMA assessed the supposed memory enhancement powers of ginkgo biloba, and found no benefits. At that point, 5 per cent of American adults took ginkgo biloba; the next year, usage dropped to 2.9 per cent, and by 2012 was down to 2 per cent.
Similarly, a large trial in 2006 tested the effects of glucosamine and chondroitin against painful knee osteoarthritis; the results, published in the New England Journal of Medicine, found no benefits. The use of glucosamine dropped from 5.2 per cent in 2005-2006 to 3.5 per cent in 2011-2012.
That, unfortunately, is the best news I can find in a new analysis of trends in dietary supplement use just published in JAMA, from a team headed by Elizabeth Kantor of Memorial Sloan Kettering Cancer Center in New York (abstract here; press release here). Those examples suggest that some people do pay attention to the evidence collected in scientific trials; unfortunately, the rest of the data suggests that most of us don’t.
The study analysed data collected as part of the National Health and Nutrition Examination Study, which regularly surveys representative groups of Americans about their health habits. It tracked supplement use from 1999 to 2012.
The overall trend was stable: In 2011-2012, 52 per cent of Americans reported using supplements, and that’s pretty much the same as it was in 1999. Within that category, there were some changes; for example, multivitamin use decreased, while vitamin D and fish oil intake increased. If it turns out that one supplement doesn’t work, we find another (or, to be more cynical, the industry finds another to sell us).
There were also some interesting subgroup trends. Women were more likely than men to take supplements, 58 to 45 per cent. Interestingly, education was also a significant predictor: 65 per cent of those with at least a Bachelor’s degree take supplements, compared to 51 per cent of those who didn’t complete university, 46 per cent of those with a high school education, and 37 per cent of those who didn’t finish high school. So it’s hard to argue that supplement use is a function of scientific illiteracy!
Accompanying the study is an editorial (full text freely available here) called “The Supplement Paradox: Negligible Benefits, Robust Consumption,” which laments the disconnect between supplement use and evidence that the supplements actually work. It’s by Pieter Cohen of Harvard Medical School, a vocal critic of unsafe supplements (who, not coincidentally, is currently being sued by a manufacturer of the supplement beta-methylphenethylamin, according to the conflict-of-interest disclosures attached to the editorial).
Cohen provides some interesting background on how supplements are (not) regulated, and why the supplement industry has mushroomed since a 1994 law that effectively hobbled Food and Drug Administration oversight of the industry, allowing manufacturers to bring products to market with no pre-approval and to make extravagant advertising claims with little to back them up. There were an estimated 4000 supplements on the market in 1994, he notes, compared to 55,000 in 2012.
He also notes that, during the period covered by the new study, the National Institutes of Health was investing US$250 million to US$300 million per year in supplement research, the vast majority of which found no benefits (or, in a few cases, increased risk).
So the riddle Cohen poses is: When the evidence suggests that (with certain exceptions, like specific multivitamins for macular degeneration) we should be avoiding supplements, why isn’t use changing? Is it because people don’t hear about the results? Because they don’t trust the scientific process? Because it’s a habit? Or is it simply because supplement advertising is so pervasive?
Under the 1994 law, advertising claims don’t have to be vetted by the FDA, and you can choose whatever flimsy evidence you want, even if it’s contradicted by a mountain of evidence. Ginkgo biloba, he notes, continues to be sold “to support mental sharpness” despite the studies that have found the opposite, including another NIH-funded randomised trial of more than 3000 people in 2009.
So what message can we take from all this? Cohen’s conclusion is that simply doing more and more studies that find no benefit from supplements won’t make much difference; it’s time for regulators, rather than scientists, to step in and make sure that products are labeled and advertised accurately.
I think we can also shoulder some personal responsibility. As someone who, in the past, has taken all sorts of things, including glucosamine, chondroitin, echinacea, and Flintstones vitamins, I definitely know how empowering it feels to be doing something that (you hope) will preserve health or fight illness and injury. I also know how these habits can become ingrained, and free from critical re-evaluation. Sometimes an unproven remedy is worth a shot – but only until it’s debunked.
