Nutritional Supplements


Nutritional supplements are nutrients formulated to supplement the diet, provide nutrients that may be missing from the regular diet, or to correct known deficiencies of specific nutrients. Nutrients, including vitamins and minerals, are as essential to human life as water, carbohydrates, protein, and fats but are required in relatively smaller amounts, hence the common term micronutrients. In the United States, the legal definition of a nutritional supplement (from Section 3 of the Dietary Supplement Health and Education Act of 1994 or DSHEA) specifies formulations of vitamins, minerals, herbs, other botanicals (except for tobacco), amino acids as metabolites or certain concentrations of these nutrients. However, legal definitions of supplements may vary from country to country. Supplements are prepared in various forms, including tablets and capsules for oral administration, chewable tablets, and liquid formulas. The nutrients in various supplement formulations can be extracted from food sources or manufactured synthetically. The U.S. Food and Drug Administration (FDA) requires that labels list precise amounts of each constituent in a single dose of the supplement.


Nutritional supplements are taken to support optimum nutrition for overall health, to supplement the diet with nutrients that may not be obtained from the diet, and to help treat or prevent acute and chronic disease. Many people take nutritional supplements to increase overall strength, endurance, mental ability, or other traits. Nutritional supplements are scientifically formulated to provide essential nutrients, herbs, or active metabolic compounds such as amino acids that may not be obtained in sufficient amounts from an individual's diet. Some people may have nutritional deficiencies, attributed either to illness, age, inherited deficiencies, or difficulty assimilating certain nutrients from foods. Some individuals may also need to supplement the diet to create higher circulating levels of a certain nutrient to achieve a desired effect or response. For example, some pre- and postmenopausal women may be advised to take calcium supplements, since reduced estrogen levels at that time of life reduce circulating calcium levels and may result in osteopenia or osteoporosis. In mid-winter, when hours of sunlight are diminished, some individuals may lack sufficient sunderived vitamin D and will experience fatigue and lack of energy. Vitamin D supplements are needed to restore circulating levels of this important vitamin and restore energy levels as well. The use of other common supplements is supported by the medical community, including the use of folic acid during pregnancy and for patients taking certain prescription drugs, and the use of vitamin B12 and vitamin D for people who follow a vegan diet and eat no meat or dairy products containing these essential nutrients.


A central issue surrounding the sale and use of supplements is the question of whether specific products produce the results claimed by manufacturers. Some people are satisfied with anecdotal evidence provided by friends, family, or the media. Such individuals are not concerned that the best scientific evidence available indicates that most reasonably healthy individuals in the developed world receive an adequate supply of essential nutrients in all but the worst of diets and that purchasing multivitamins may be an unnecessary medical expense. Increasingly, as mainstream medicine, including the U.S. National Institutes of Health, investigates the effectiveness of certain nutritional approaches to reducing symptoms of acute and chronic diseases, controlled studies were conducted to evaluate how well certain nutritional supplements produce their results. The National Center for Complementary and Alternative Medicine (NCCAM) collected data on the efficacy of various nutritional supplements. The NCCAM found that some claims for supplements are supported by scientific evidence, whereas other claims lack adequate investigation and may remain unconfirmed. Results are available at The NCCAM website.

Recommended dosage

The FDA has established recommended dosages, called recommended daily intakes (RDIs), for vitamins and minerals but not for most other supplements. A chart listing those RDIs is available on the FDA website. For all other products, manufacturers often suggest recommended dosages on product labels based on the results of relevant clinical or laboratory studies that have been conducted.


Except for vitamins and minerals that are supported by FDA regulations, nutritional supplements generally lack adequate information for consumers about contraindications and possible side effects. However, although as of 2017 most nutritional supplements had not undergone rigorous testing as required of drugs, considerable anecdotal and circumstantial evidence was available in books and online, much of it provided by healthcare professionals, herbalists, or scientists specializing in nutrition:

Meal replacement—
A commercial product, usually in the form of a drinkable liquid, to be taken in place of a regular meal of solid foods. Such products are commonly used as part of a weight-loss program but can also be used by individuals with special dietary problems not easily treated with regular diets.
A nutritional supplement that typically contains all essential vitamins and minerals deemed necessary for optimum nutrition and overall health.

It is in consumers' best interest to obtain as much information as possible about a supplement before beginning to use that product regularly. Individuals are also cautioned against taking excessive amounts of supplements or megadoses. Taking more than the RDI may lead to side effects that could be harmful to one's health. Also, all individuals and especially pregnant women are advised to discuss the use of nutrition supplements with their physician before taking them. However, to the extent that a supplement has beneficial effects, and all necessary cautions are observed, there is no reason not to use nutrition supplements. Meanwhile, the best alternative to taking dietary supplements is to consume a more nutritious diet with adequate amounts of carbohydrates, fats, protein, vitamins and minerals.



Potentially dangerous interactions may occur between nutritional supplements and prescription and over-the-counter (OTC) drugs or other ingested products. Some potential interactions identified as of 2017 are:



Greenwood, Mike, and Matthew B. Cooke, editors. Nutritional Supplements in Sports and Exercise, 2nd ed. New York: Springer, 2015.


Blumberg, J. B., B. Frei, V. L. Fulgoni, et al. “Vitamin and Mineral Intake Is Inadequate for Most Americans: What Should We Advise Patients About Supplements?” Journal of Family Practice 65 (September 2016): S1–8.

Cramer, J. T., A. J. Cruz-Jentoff, F. Landi, et al. “Impacts of High-Protein Oral Nutritional Supplements Among Malnourished Men and Women with Sarcopenia: A Multicenter, Randomized, Double-Blinded Controlled Trial.” Journal of the American Medical Directors Association. 17 (November 2016): 1044–55.

Kantor, E.D.,C. D. Rehm, M. Du, et al. “Trends in Dietary Supplement Use Among US Adults from 1999–2012.” JAMA 316 (October 2016): 1464–74.

Matondo, F. K., K. Takaisi, A. B. Nkuadiolandu, et al. “Spirulina Supplements Improved the Nutritional Status of Undernourished Children Quickly and Significantly: Experience from Kisantu, the Democratic Republic of the Congo.” International Journal of Pediatrics. Published electronically September 2016. doi: 10.1155/2016/1296414.

Tesfaye, M., P. Kaestel, M. F. Olsen et al. “The Effect of Nutritional Supplementation on Quality of Life In People Living with HIV: A Randomised Controlled Trial.” Tropical Medicine and International Health 21 (June 2016): 735–42.


WebMD. “FAQs About Dietary Supplements.” (accessed November 12, 2016).


American Dietetic Association, 120 S. Riverside Plaza, Suite 2000, Chicago, IL, 60606-6995, (800) 877-1600,, .

American Nutrition Association, PO Box 262, Western Springs, IL, 60558, (301) 435-3663, Fax: (708) 246-3663, .

Office of Dietary Supplements, National Institutes of Health, 6100 Executive Boulevard, Room 3B01, MSC 7517, Bethesda, MD, 20892-7517, (301) 435-2920, Fax: (301) 480-1845,, .

David E. Newton, AB, MA, EdD
L. Lee Culvert

  This information is not a tool for self-diagnosis or a substitute for professional care.