Benefits and Risks of Dietary Supplements

Dietary supplements have both benefits and risks.
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Dietary supplements are products designed to augment your daily intake of nutrients, including vitamins and minerals. Many are safe and offer significant health benefits, but there are some that pose health risks, especially if overused. Dietary supplements include amino acids, fatty acids, enzymes, probiotics, herbals, botanicals, and animal extracts.

In addition to vitamins and essential minerals, popular supplements include:


Normally, you should be able to get all the nutrients you need from a balanced diet. However, supplements can provide you with extra nutrients when your diet is lacking or certain health conditions trigger a deficiency (such as cancer, diabetes, or chronic diarrhea).

In most cases, a multivitamin/mineral supplement will provide all the micronutrients your body needs. They are generally safe because they contain only small amounts of each nutrient (as measured by the daily value, or DV).

Individual nutrients are also available as supplements, usually in doses larger than your typical multivitamin. They can be used to treat a deficiency, such as an iron deficiency, or reduce the risk of a medical condition, such as hypertension. ​

For example, large doses of vitamin B3 (niacin) can help raise "good" high-density lipoprotein (HDL) cholesterol, while folic acid has long been used to reduce the risk of a birth defect called spina bifida.

Unless a specific deficiency is identified, a supplement is usually not necessary if you eat and exercise properly. The appropriate use of supplements can help you avoid side effects and toxicities associated with overuse.


In the United States, dietary supplements are not regulated as strictly as pharmaceutical drugs; manufacturers do not have to prove that they are either safe or effective. The U.S. Food and Drug Administration (FDA) doesn't even determine whether dietary supplements are effective before they are shipped to market shelves.

With that said, the FDA maintains a list of tainted or potentially harmful products marketed as dietary supplements. The worst offenders are usually weight loss aids, "natural" sexual enhancement pills, and supplements targeted at bodybuilders.

Supplement manufacturers have to follow certain labeling guidelines, including what they can say and not about the purported benefits.

That doesn't stop manufacturers from claiming, often misleadingly, that their product can "boost the immune system" or "treat arthritis" even if there is little scientific evidence to support the claims. Generally speaking, only the most serious infractions are acted upon by the FDA.

Problems to Lookout For

While most dietary supplements are safe as long as you follow the product instructions, large doses of certain nutrients can have adverse effects. You can even overdose on certain supplement, risking serious harm and death.

Among some the harmful interactions or dosing concerns:

  • Vitamin K can reduce the effectiveness of blood thinners like Coumadin (warfarin).
  • Vitamin E can increase the action of blood thinners, leading to easy bruising and nosebleeds.
  • St. John’s wort can accelerate the breakdown of many drugs, including antidepressants and birth control pills, thereby reducing their effectiveness.
  • Antioxidants like vitamins C and vitamin E can reduce the effectiveness of some types of cancer chemotherapy.
  • High-dose vitamin B6 (pyridoxine), when used for a year or more, can cause severe nerve damage. Vitamin B6 can also reduce the effectiveness of the anti-seizure drug Dilantin (phenytoin) and levodopa (used to treat Parkinson's disease). 
  • Vitamin A used with retinoid acne medications such as Accutane (isotretinoin) and Soriatane (acitretin) can causes vitamin A toxicity.
  • Vitamin B3 (niacin), when used with statins, may increase the risk of rhabdomyolysis (the abnormal breakdown of muscle tissue).
  • Iron and calcium supplements can reduce the effectiveness of antibiotics, namely tetracyclines and fluoroquinolones, by as much as 40 percent.
  • Vitamin C, when taken in doses exceeding 2,000 milligrams, can cause nausea and severe diarrhea.
  • Selenium, boron, and iron supplements can be toxic if taken in large amounts.

Advise your healthcare provider about any supplements you plan to take as well as any medications you are currently taking, whether they be pharmaceutical, over-the-counter, herbal, traditional, or homeopathic.

For the utmost safety and quality, choose supplements tested and approved by a certifying body such as the U.S. Pharmacopeia (USP). Never use expired supplements.

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Article Sources

  1. U.S. Food and Drug Administration. Tips for Older Dietary Supplement Users. Updated November 29, 2017.

  2. Afolayan AJ, Wintola OA. Dietary supplements in the management of hypertension and diabetes - a reviewAfr J Tradit Complement Altern Med. 2014;11(3):248–258. doi:10.4314/ajtcam.v11i3.35

  3. National Institutes of Health Office of Dietary Supplements. Niacin. Updated July 9, 2019.

  4. Centers for Disease Control and Prevention. Folic Acid Helps Prevent Some Birth Defects. Updated January 7, 2019.

  5. U.S. Food & Drug Administration. Tainted Products Marketed as Dietary Supplements. Updated May 7, 2019.

  6. U.S. Food & Drug Administration. Center for Biologics Evaluation and Research 2003. Updated March 2, 2016.

  7. U.S. Food and Drug Administration. Fortify Your Knowledge About Vitamins. Updated February 2, 2009.

  8. National Institutes of Health Office of Dietary Supplements. Dietary Supplements: What You Need to Know. Updated June 17, 2011.

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