expert opinion

The challenge of studying dietary supplements

June 15, 2014

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Jeffrey B. Blumberg, PhD, Friedman School of Nutrition Science and Policy, Tufts University, Boston, USA

“The study of nutritional supplements can have many blind alleys. Because most people who take supplements are proactive about their health in general, it is inherently misleading to make observational studies that compare the health of supplement users to nonusers. Instead, clinicians follow what is known as evidence- based dietetics practice, which requires the use of systematically reviewed scientific evidence in decision making. All studies are not created equal, and many nutrient studies have yet to be substantiated with similar research and results. But randomized controlled trials, the gold standard for pharmaceuticals, are also beset with problems when nutrients are the study object. Most large clinical trials of nutritional supplements are done with healthier-than-average people, such as doctors or nurses. Researchers do not test partici- pants’ baseline blood levels or biomarkers of nutrients prior to supplementation. Unlike in pharmaceutical studies, the control group is also getting some amount of the nutrient in question just from eating. Finally, supplementing healthy people for years or decades and measuring who develops heart disease or cancer would cost billions of dollars. Even a huge-selling supplement would not justify that level of spending.

On the other hand, most people in the US do not get nutrient levels recommended by the Food and Drug Administration (FDA) through diet, mostly because they do not eat nearly enough fruits, vegetables, and fish. Data from the National Institutes of Health show that more than 80% of Americans more than four years old do not consume enough vitamins D and E (1). More than one-third fall short on calcium and vitamins A and C. Other essential nutrients, such as omega-3 fatty acids and selenium, are likely also lacking but there are no government-recommended dietary intake levels. Routine deficiencies of essential nutrients prevent the body from functioning optimally and may be reason enough to take supplements, even though deficiency diseases such as scurvy or pellagra are extremely rare these days. Supplements can help address defi- ciencies in people who are malnourished as a result of low appetite; who do not absorb vitamins well from their diet or have pancreatic, liver, or kidney disease; who suffer from alcoholism; or who have had gastric bypass. Patients who have had a heart attack or suffer from coronary artery disease have been shown in several studies to benefit from omega-3 fatty acid supplements (2). Those with abnormally high blood levels of triglycerides may be prescribed a pharmaceutical-grade omega-3 supplement.

Currently, many scientists are gathering evidence about short-term benefits such as strengthened immune response and delayed cognitive decline. In the longer term, they also hope to tackle the bigger challenge: proving that supplements reduce the risk of cancer, cardiovascular diseases and Alzheimer’s disease. A recent study showed that supplementation with alpha-tocopherol, a version of the antioxidant vitamin E, slowed the rate of progression of Alzheimer’s disease by 6.2 months compared with a placebo (3). The vitamin E group had a better outcome than a group taking the Alzheimer’s drug memantine. Also, a new study showed that omega-3 fatty acids – docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) – found in fish, reduce the risk of adverse coronary incidents in the general population (4). Supplements may do better than help stave off nutrient deficiencies or insufficiencies. Scientists are striving at designing studies which investigate the impact of supplementation on healthy people. The challenge is to prove in what way the supplement group stays healthy compared with a control group that takes a placebo.”

Based on: Bomgardner M. M. Supplemental Science. Chemical & Engineering News. April 2014; 92(16):10–15.

1. Fulgoni V. L. 3rd. et al. Foods, fortificants, and supplements: where do Americans get their nutrients? J. Nutr. 2011; 141:1847–1854.

2. Delgado-Lista J. et al. Long chain omega-3 fatty acids and cardiovascular disease: a systematic review. Br J Nutr. 2012; 107(Suppl 2):S201–213.

3. Dysken M. W. et al. Effect of Vitamin E and Memantine on Functional Decline in Alzheimer Disease. JAMA. 2014; 311(1):33–44.

4. Chowdhury R. et al. Association of Dietary, Circulating, and Supplement Fatty Acids With Coronary Risk: A Systematic Review and Meta-analysis. Ann Intern Med. 2014; 160(6):398–406.