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Are dietary supplements healthful or harmful?

Prescription drug use in the US has grown significantly over the past decade, with 15% of American adults taking 5 or more drugs in 2012, compared to 8.2% in 2000. At the same time, recent studies show a similar increase in use of supplements, especially for children and teens. About a third of children and adolescents use dietary supplements such as multivitamins or omega 3 fatty acids, according to a research letter in JAMA Pediatrics

About a third of children and adolescents use dietary supplements.

What’s the big deal about more Americans taking supplements? When I was growing up, we got Flintstones vitamins every day and considered them perfectly healthy (unless you ate too many at once).

While supplements are often seen as harmless because they don’t need a prescription to obtain, vitamins and other supplements are not as benign as they seem. In JAMA Forum, health policy researcher Aaron Carroll, MD points out the reasons why growing supplement use is  problematic:

  • Supplement use is largely unregulated. Unlike prescription medications, “supplement producers do not need to prove that their products work before selling them to people,” writes Carroll. The Food and Drug Administration does not review dietary supplements for effectiveness or safety before they are marketed. They’re only required to review a supplement if there is a new ingredient, but the FDA can only review it for safety, not effectiveness. This means that consumers are largely buying supplements at their own risk.
  • There’s no evidence that supplements work. Research shows that popular supplements, such as antioxidants and fish oil, do not improve health outcomes in adults, and may in fact increase mortality. The vast majority of children in the US get enough daily nutrients from their diet, and don’t need supplements, Carroll points out.
  • They can cause harmful drug-drug interactions. The more medications a person takes, whether they are prescription or over-the-counter, the greater the likelihood of an adverse drug reaction. “Although clinicians spend a large amount of time checking for potential problems in the pharmaceuticals they  prescribe, relatively little is spent on potential problems from supplements,” writes Carroll.

Carroll ends his piece by questioning the appeal of supplements – “It’s hard to understand why patients are using them in such increasing numbers,” he writes. But what Carroll does not mention is that the supplement industry has enormous power, which it has used to craft a compelling narrative (backed by “evidence”) about the benefits of supplements.

In The New York Times, Liz Szabo investigates financial interests within the booming Vitamin D industry. Szabo writes that Dr. Michael Holick, Boston University endocrinologist and fierce advocate of the health benefits of Vitamin D, receives hundreds of thousands of dollars from supplement manufacturers, makers of Vitamin D tests, and the tanning industry. Holick’s research in the early 2010s declared a Vitamin D deficiency “epidemic,” laying the groundwork for widespread testing and supplement prescriptions.

Professional societies and lab companies have also been complicit in spreading the narrative of a Vitamin D epidemic. The Endocrine Society guidelines raised the level of Vitamin D “sufficiency” higher than other professional society recommendations, such that 80% of Americans are labeled Vitamin D “deficient.” Lab companies have adopted the higher benchmark, because more people with the deficiency require more testing, which increases their profit. 

Despite all of the enthusiasm around Vitamin D, the evidence of health benefits is weak.

Despite all of the enthusiasm around Vitamin D, the evidence of health benefits is weak. The US Preventive Services Task Force recommends against Vitamin D supplements for preventing falls in older adults, and found that there isn’t enough evidence to recommend Vitamin D deficiency screening or taking Vitamin D for preventing fractures in the future.

Going back to Carroll’s question, why are so many people still taking supplements, given the lack of evidence? Once an idea is disseminated throughout the medical community and the media, it’s hard to put the cat back in the bag (or put the pills back in the bottle). Supplement manufacturers have billions on the line, and will do whatever they can to push the narrative that supplements make you healthy. So far, this appealing narrative has mostly drowned out evidence questioning the benefits of supplements. Turning the tide on unnecessary supplements is going to be an uphill climb.    

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