Dietary Supplements: What You Need to Know Before You Buy

What Are Dietary Supplements?

Dietary supplements are products intended to add to or supplement your diet, and they are different from conventional food. They are ingested, meaning you take them by mouth, and they come in many forms, including tablets, capsules, soft gels, gel caps, powders, bars, gummies, and liquids.

In the United States, the legal definition of a dietary supplement is set by the Dietary Supplement Health and Education Act of 1994 (DSHEA). Under DSHEA, a dietary supplement is a product that is intended to supplement the diet and contains one or more of these dietary ingredients: a vitamin, a mineral, an herb or other botanical, an amino acid, a dietary substance used to supplement the diet by increasing total dietary intake, or a concentrate, metabolite, constituent, extract, or combination of these ingredients.

Dietary supplements are meant to help you meet your nutritional needs, but they are not designed to replace a healthy eating routine. As the National Institutes of Health notes, supplements cannot take the place of the variety of foods that are important to a healthy diet.

Sources: NIH Office of Dietary Supplements, U.S. Food and Drug Administration, Journal of the Academy of Nutrition and Dietetics

How Dietary Supplements Are Regulated in the US

In the United States, the Food and Drug Administration (FDA) regulates dietary supplements as a subcategory of food under the Dietary Supplement Health and Education Act of 1994 (DSHEA). The FDA does not approve dietary supplements before they are marketed; instead, manufacturers and distributors are responsible for ensuring a product is safe before it goes on the market.

The FDA can take action against a supplement that is unsafe or that is marketed as a drug. A product intended to treat, diagnose, cure, or prevent disease is legally a drug, even if it is labeled as a dietary supplement.

While the FDA oversees product safety and labeling, the Federal Trade Commission (FTC) regulates dietary supplement advertising. The FTC requires that advertising be truthful and not misleading, and it can take enforcement action against false or deceptive claims. Understanding the distinct roles of these agencies can help you navigate supplement marketing with a clearer eye.

Sources: NIH Office of Dietary Supplements, U.S. Food and Drug Administration, Journal of the Academy of Nutrition and Dietetics

Types of Dietary Supplements: Vitamins, Minerals, Herbs

Dietary supplements fall into several broad categories based on the dietary ingredients they contain. The most common types are vitamins, minerals, herbs or other botanicals, amino acids, and other dietary substances. Products may use one type alone or combine several.

Vitamins and minerals are essential nutrients your body needs to function correctly. They are among the most widely used supplements. Data from the CDC for 2017–2018 showed that multivitamin-mineral products, vitamin D, and omega-3 fatty acids were the most common types used by U.S. adults.

Herbal and botanical supplements come from plants and may be sold as extracts, concentrates, or in whole-plant forms. Amino acids, which are the building blocks of proteins, are also available as supplements. The legal definition also includes dietary substances intended to supplement the diet by increasing intake, as well as metabolites, constituents, and combinations of these ingredients.

This list is not exhaustive, but it reflects the major categories defined by law and observed in national surveys.

Sources: NIH Office of Dietary Supplements, Journal of the Academy of Nutrition and Dietetics, CDC National Center for Health Statistics

How to Evaluate Supplement Quality and Safety

Evaluating a supplement's quality and safety involves looking at multiple factors. According to the NIH, a supplement's safety depends on its chemical makeup, how it works in the body, how it is prepared, and the amount you take. There is no one-size-fits-all answer, but you can ask informed questions.

Start by reading the label and the Supplement Facts panel. Look for the word "supplement" on the label and check the list of ingredients. Be cautious about products that make bold promises or claim to treat, diagnose, cure, or prevent disease—those claims place the product outside the dietary supplement category.

When in doubt, talk to your healthcare provider, especially if you have a medical condition or take medication.

• Check the label for the supplement name and any warnings.
• Review the amount of each ingredient against recommended daily values.
• Be skeptical of products that guarantee results or sound too good to be true.
• Ask your healthcare provider about potential interactions with your medications.

Sources: NIH Office of Dietary Supplements, U.S. Food and Drug Administration

Understanding Supplement Labels and Claims

Supplement labels must identify the product as a dietary supplement. Beyond that, they include a Supplement Facts panel that lists serving size, amount per serving, and percent Daily Value for nutrients. This information helps you understand what you are consuming.

Labels can also make certain claims, but the FDA distinguishes between structure/function claims, which describe how a nutrient affects the body's structure or function, and disease claims. If a label implies the product can treat or prevent a disease, the product would be subject to drug regulations, not supplement rules.

The phrase "natural" on a label does not automatically mean safe. As the NIH points out, natural does not always equal safe. Some natural botanical products, such as comfrey and kava, can harm the liver.

Sources: NIH Office of Dietary Supplements, Journal of the Academy of Nutrition and Dietetics

Risks and Interactions: What to Watch Out For

Dietary supplements can have strong effects on the body, and they are not without risks. They can cause side effects, interact with medications, interfere with lab tests, or be dangerous if you are having surgery.

For example, vitamin K can reduce the ability of the blood thinner warfarin to prevent clotting. St. John's wort can speed the breakdown of many medicines, reducing their effectiveness—this includes some antidepressants, birth control pills, heart medications, anti-HIV medications, and transplant drugs. Antioxidant supplements such as vitamins C and E might reduce the effectiveness of certain cancer chemotherapies.

Taking more than you need costs money and may raise your risk of side effects. Specific examples: too much vitamin A can cause headaches, liver damage, reduced bone strength, and birth defects. Excess iron can cause nausea and vomiting and may damage the liver and other organs.

Because of these risks, it is wise to talk with your healthcare provider before adding a supplement to your routine, particularly if you take medications or have a chronic condition.

Sources: NIH Office of Dietary Supplements, U.S. Food and Drug Administration

How to Talk to Your Healthcare Provider About Supplements

If you are considering a dietary supplement, a conversation with your doctor, pharmacist, or dietitian can help you make an informed choice. Bring a list of all the products you take, including the dose and how often. This includes supplements, prescription medications, and over-the-counter drugs.

Ask whether the supplement is necessary for your specific situation. The Academy of Nutrition and Dietetics does not recommend routine, indiscriminate use of micronutrient supplements for chronic disease prevention, because there is little evidence to support that approach. However, supplements may be warranted when your diet falls short of meeting your needs—such as during pregnancy, with certain medical conditions, or if you have malabsorption.

Your provider can help you weigh potential benefits, risks, and interactions. They can also advise on the right dose, because more is not always better.

Sources: NIH Office of Dietary Supplements, Journal of the Academy of Nutrition and Dietetics