Are dietary supplements useful?

September 15, 2014

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Balz Frei, PhD, Linus Pauling Institute, Oregon State University; Corvallis, Oregon, USA
Bruce N. Ames, PhD, Children's Hospital Oakland Research Institute; Oakland, USA
Jeffrey B. Blumberg, PhD, Friedman School of Nutrition Science and Policy, Tufts University; Boston, Massachusetts, USA
Walter C. Willett, MD, DrPH, Harvard School of Public Health; Boston, Massachusetts, USA

“A recent publication (1) concluded that ‘the case is closed – supplementing the diet of well-nourished adults with (most) mineral or vitamin supplements has no clear benefit and might even be harmful’. First, it is unscientific to make recommendations on the value of dietary supplementation using the results of clinical trials that have not assessed participants’ nutritional status. Second, the authors ignored decades of nutrition research and diet monitoring of the US population to reach this misleading conclusion. Although a well-balan- ced diet is the best way to get one’s essential nutrients (except vitamin D and, for vegans and many older adults, vitamin B12), few people in the United States follow the Dietary Guidelines for Americans. Consequ- ently, most US citizens are not ‘well-nourished’ and do not meet the Institute of Medicine’s recommendations for the dietary intake of vitamins and essential minerals. More than 93%, 61%, and approximately 50% of adults in the United States do not achieve the Estimated Average Requirement of vitamins D and Emagnesium, and vitamin A and calcium, respectively, through their diet, including enriched and fortified foods (2). Furthermore, 98% and 71% do not meet the Adequate Intake of potassium and vitamin K, respectively (2). Many of these percentages are even higher among subpopulations with increased micronutrient needs, in- cluding older adults, African Americans, and the obese. Conversely, those taking a daily multivitamin and mineral supplement formulated at approximately the Daily Value do manage to fill many of these nutritional gaps effectively, safely, and at low cost: A high-quality multivitamin and mineral supplement costs as little as three cents per day (3), and long-term use is not associated with any adverse health effects (2, 4).

The aforementioned recent publication (1) states that ‘beta-carotene, vitamin E, and possibly high doses of vitamin A supplements increase mortality’. Only approximately 0.1% of adults in the United States exceed the Tolerable Upper Intake Level (UL) of vitamin E because of high-dose supplement use, and approximately 1.1% exceed the UL of vitamin A (2). It is widely accepted that vitamin A should not be consumed over the long term in amounts exceeding the UL because it may cause hypervitaminosis A and birth defects. It is also acknowledged that smokers should avoid high doses of beta-carotene supplements because of an increased risk of lung cancer. A meta-analysis of randomizedcontrolled trials (RCTs) reporting that high-dose vitamin E supplements increase mortality (1) has been refuted by several, more comprehensive meta-analyses (5).

The known biological functions of micronutrients are maintaining normal cell and tissue function, and aiding metabolism, growth, and development by serving as essential cofactors or structural components of thou- sands of enzymes and other biomolecules, among other functions. For example, vitamins A and D, iron, and zinc play critical roles in innate and adaptive immunity, and folate is required for normal neurologic develop- ment. A multivitamin and mineral supplement containing folic acid dramatically decreases the risk of neural tube defects and is recommended for women of childbearing age. Multivitamin and mineral supplements may also help decrease the risk of developing chronic diseases. The largest and longest RCT of a multivitamin and mineral supplement conducted to date – the PHS II (Physicians’ Health Study II) – found a statistically significant 8% reduction in total cancer incidences in male physicians (12% when excluding prostate cancer) and a statistically significant 9% and 13% reduction in total and nuclear cataract, respectively (4). These findings are consistent with those of several other RCTs and are even more impressive given that conven- tional RCT designs are limited in their ability to reveal the benefits of nutrients – in contrast to drugs – for chronic diseases (6).

In summary, taking a daily multivitamin and mineral supplement will not only help fill known nutritional gaps in the diets of most people in the United States (thereby ensuring normal body function and supporting good health) but may also have the added benefit of helping to reduce the risk of some chronic diseases. To call the case closed, deny the value of further research, and label multivitamin and mineral supplements useless, harmful, and a waste of money (1) is wrong, is not based on the established science for their primary indi- cation, and misinforms the public and the medical community.”

Based on: Frei B. et al. Enough is enough [Letter]. Ann Intern Med. 2014; 160(11):807.

References

  1. Guallar E. et al. Enough is enough: Stop wasting money on vitamin and mineral supplements [Editorial]. Ann Intern Med. 2013; 159:850-851.
  2. Fulgoni V. L. 3rd et al. Foods, fortificants, and supplements: Where do Americans get their nutrients? J Nutr. 2011; 141:1847-1854.
  3. ConsumerLab.com. 2014. Accessed at 
    https://www.consumerlab.com/reviews/multivitamin_multimineral_supplements/multivitamins/ in April 2014.
  4. Gaziano J. M. et al. Multivitamins in the prevention of cancer in men: the Physicians' Health Study II randomized controlled trial. JAMA. 2012; 308:1871-1880.
  5. Abner E. L. et al. Vitamin E and all-cause mortality: a meta-analysis. Curr Aging Sci. 2011; 4:158-170.
  6. Blumberg J. et al. Evidence-based criteria in the nutritional context. Nutr Rev. 2010; 68:478-484.