Dietary Supplements Basics

Although each vitamin has unique functions, deficiencies are uncommon when people consume a varied diet rich in fruits, vegetables, whole grains, dairy or fortified alternatives, and protein foods. Nutrition scientists focus on overall dietary patterns because foods contain many nutrients that work together to support health.

Still, many people wonder whether they need a vitamin or mineral supplement. Others are drawn to products that claim to boost energy, build muscle, support immunity, improve gut health, or promote weight loss.

You’re not alone. More than half of U.S. adults report using dietary supplements.^[1]

But are supplements safe, effective, and necessary? Let’s take a closer look.

With so many people taking supplements, it’s worth asking:

• Are they safe?

• Do they really work?

• Who actually needs them?

Let’s explore these questions together.

What Counts as a Dietary Supplement?

A dietary supplement is a product that:

• Adds nutrients or other substances to the diet.

• Contains one or more ingredients such as vitamins, minerals, herbs, botanicals, amino acids, or enzymes.

• Is taken by mouth (pill, capsule, tablet, or liquid).

• Is clearly labeled as a “dietary supplement.”

How Are Supplements Regulated?

Dietary supplements are regulated by the Food and Drug Administration (FDA), but not in the same way as foods or prescription drugs. Under the Dietary Supplement Health and Education Act (DSHEA) of 1994, manufacturers—not the FDA—are responsible for ensuring that supplements are safe before they are sold.^[2]

Unlike prescription drugs, supplements do not have to prove they are safe or effective before reaching the market. The FDA can investigate products, issue warnings, or remove supplements from the market if they are found to be unsafe.

To improve quality control, the FDA established Good Manufacturing Practices (GMPs), which set standards for supplement production, storage, and testing.^[3]

Because the FDA cannot evaluate every supplement sold, consumers should use caution when selecting and using these products.

Are Dietary Supplements Safe?

Because safety oversight occurs after products reach the market, supplement safety is largely in manufacturers’ hands. Unfortunately, not all companies follow best practices—especially when profits are at stake.

According to the FDA, supplements have been recalled for contamination (with bacteria, pesticides, or heavy metals) and for containing incorrect or misleading ingredient amounts. ^[4]

Here are some key takeaways from the National Center for Complementary and Integrative Health (NCCIH):^[5]

• Labels aren’t always accurate. Some “supplements” have been found to contain prescription drugs such as warfarin or phenytoin.

• Illegal claims are common. In one government study, 20% of weight-loss or immune-support supplements made false or illegal claims.

• Interactions can be dangerous. For instance, St. John’s wort can reduce the effectiveness of some medications.

• “Natural” doesn’t always mean safe. Ephedra, once used in energy and weight-loss supplements, caused heart attacks and deaths before being banned in 2004.

• Supplements can cause real harm. A 2015 study estimated 23,000 emergency room visits each year in the U.S. are linked to dietary supplements—often due to heart problems from energy or weight-loss products or swallowing issues in older adults.

• “Certified” or “standardized” isn’t a guarantee. These terms are marketing tools, not legal standards.

If you ever experience a reaction to a supplement, you can report it through the U.S. Health and Human Services Safety Reporting Portal.

With current regulations, the safety of dietary supplements is the manufacturer’s responsibility. Unfortunately, manufacturers don’t always have the public’s best interest in mind, especially when there is a profit to be gained.

Do Supplements Really Work?

The effectiveness of dietary supplements varies widely. Some supplements may be helpful in specific situations, while others have little evidence to support their claims. Supplements cannot legally claim to diagnose, treat, cure, or prevent disease, so many products use broad statements such as “supports immunity” or “promotes heart health.”

Research suggests that most multivitamin/mineral supplements provide little benefit for preventing chronic disease in otherwise healthy adults.^[6]

🎥 Watch & Learn

Video: “Supplements and Safety” – PBS Frontline (54:11)

An in-depth look into the hidden dangers of vitamins and supplements—a multibillion-dollar industry with limited FDA oversight. Produced by FRONTLINE, The New York Times, and the Canadian Broadcasting Corporation, the documentary investigates marketing, regulation, and cases of contamination and serious health risks.

Attributions

This section is an adaptation of "Dietary Supplements" in Nutrition: Science and Everyday Application, v. 1.0 by Alice Callahan, PhD; Heather Leonard, MEd, RDN; and Tamberly Powell, MS, RDN licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.

Figure 8.31 shows the USP verification mark, which indicates that a supplement has met these quality standards.[footnote]U.S. Pharmacopeia (USP). USP Verified Dietary Supplements Program. https://www.usp.org/dietary-supplements ↵