More than half of American adults continue to use nutritional supplements despite research that shows they may have few benefits, a new study finds. Use of nutritional supplements remained stable among adults between 1999 and 2012, whereas multivitamin use decreased slightly during the same period.
Elizabeth D. Kantor, PhD, from the Department of Epidemiology and Biostatistics, Memorial Sloan Kettering Cancer Center, New York City, and colleagues report their findings in an article published in the October 11 issue of JAMA.
Results from observational studies have yielded mixed results regarding the health benefits of individual supplements or multivitamins/multiminerals (MVMM), and randomized clinical trials have often not supported benefits of these supplements," the researchers write. "Furthermore, some research has indicated that the use of selected supplements at high doses may have adverse effects, generating some skepticism regarding their use."
In an accompanying editorial, Pieter A. Cohen, MD, from the Department of Internal Medicine, Cambridge Health Alliance, and Harvard Medical School, Boston, Massachusetts, reiterates that point: "During the past 2 decades, a steady stream of high-quality studies evaluating dietary supplements has yielded predominantly disappointing results about potential health benefits, whereas evidence of harm has continued to accumulate."
In the current study, Dr Kantor and colleagues analyzed data from the National Health and Nutrition Examination Survey, a nationally representative, cross-sectional survey on noninstitutionalized civilians living in the United States. The analysis was conducted in seven 2-year cycles (1999 - 2000 through 2011 - 2012), and the researchers considered each cycle as an independent sample.
The study analysis included 37,958 (sample size per cycle, 4863 - 6213) adults aged 20 years or older who completed in-home interviews that asked about their supplement use.
Overall supplement use did not change during the study period, with 52% of respondents reporting use in both the 1999 to 2000 cycle and the 2011 to 2012 cycle (difference, 0.0%; 95% confidence interval [CI], -3.6% to 3.6%).
The proportion of respondents reporting use of four or more supplement products also showed no significant change, with 8.7% of respondents saying they used four supplement products in 1999 to 2000 and 9.9% in 2011 to 2012 (difference, 1.1%; 95% CI, -0.8% to 3.0%).
The authors also found a decrease in the use of some individual vitamins and minerals, including vitamin C, vitamin E, and selenium. However, the decrease was not universal, the researchers note. "For example, vitamin D, the most commonly used vitamin in 2011-2012, remained stable overall; however, use excluding MVMM increased almost 4-fold (5.1% in 1999-2000 vs 19% in 2011-2012; difference, 14% [95% CI, 12%-17%])."
The authors note that the use of several nonvitamin, nonmineral supplements increased over the course of the study. For example, use of omega-3 fatty acids rose almost sevenfold, with 1.9% of adults reporting they used them during 1999 to 2000 and 13% reporting their use during 2011 to 2012 (difference, 11%; 95% CI, 9.4% - 13%). A ninefold increase in the use of fish oil largely drove that increase, but alphalinolenic acid or flaxseed use also rose.
Several sociodemographic variables were associated with supplement use, including increasing age (72% of adults aged 65 years or older vs 40% of adults aged 20 - 39 years), female sex (58% vs 45% of men), non-Hispanic white adults (58% vs 29% among Mexican Americans), and educational level (65% among those with 4 or more years of college education vs 37% among those with less than a high school education).
"What strikes me as very interesting is how the use of supplements remains quite high, [with] more than a majority of Americans using [them] despite this consistent number of studies showing little or marginal benefit to any of these supplements," Dr Cohen said in an accompanying podcast.
Clinicians should include supplements when reviewing medications with patients and consider the possibility of an adverse effect when discussing symptoms with patients, Dr Cohen writes in the editorial.
"It is now known that many supplements contain pharmaceutically active botanicals, which can have important clinical effects. For example, red yeast rice, yohimbe, and caffeine all have pharmacological effects, and although ephedra has been banned, a variety of synthetic drugs have replaced ephedra as stimulants in many sports and weight loss supplements," he explains. "Reporting suspected adverse effects of supplements is also critical. The [US Food and Drug Administration] relies on physicians and consumers to report adverse events via MedWatch to remove hazardous supplements from the marketplace."
"The current study...should also lead funders and legislators to reconsider their priorities with respect to supplements. Given the current regulatory framework, even high-quality research appears to have only modest effects on supplement use. Future efforts should focus on developing regulatory reforms that provide consumers with accurate information about the efficacy and safety of supplements and on improving mechanisms for identifying products that are causing more harm than good," Dr Cohen concludes.
The study authors have disclosed no relevant financial relationships. Dr Cohen disclosed receiving funds to buy research supplies from Consumers Union. At the time of this editorial submission, Dr Cohen disclosed that he was a defendant in a civil suit brought by a supplement manufacturer involving ß-methylphenethylamine.
JAMA. 2016;316:1453-1454, 1464-1474. Article abstract, Editorial extract
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Supplement Use Stable, Despite Research Questioning Benefit. Medscape. Oct. 4, 2016.