What Are Dietary Supplements and Do They Work?

dietary supplementsThe use of dietary supplements in the United States has grown dramatically over the past 10-20 years. With more and more people trying to improve their health in a quick and easy way, it’s no wonder that many turn to supplements. Advertisements for supplements commonly promise fast results, and “regular” people provide testimonials, swearing by the product. But are these supplements really worth the hype (and the money)? If it’s on the shelf at the store, it must be safe and effective, right?

Not necessarily. Let’s take a closer look at the truth behind dietary supplements and discover what they are and whether they work.

What are dietary supplements?

The term “dietary supplement” refers to a broad range of products including vitamins, minerals, herbs, amino acids, enzymes, extracts, and probiotics. They are classified in four main categories:

  1. Vitamins and minerals are substances required for normal metabolism, essential in small amounts to maintain good health, promote growth, and regulate body functions. This category includes supplements like multivitamins, calcium, iron, vitamin D, or vitamin C.
  2. Specialty supplements are substances that cannot be classified in other supplement categories. This category includes supplements like fish oil, probiotics, melatonin, CoQ10, and amino acids.
  3. Herbals and botanicals are plants or plant parts valued for their medicinal or therapeutic properties, flavor, or scent. This category includes such supplements as garlic, cranberry, echinacea, and ginseng.
  4. Sports nutrition and weight management substances are designed to aid in physical performance or weight loss. This category includes supplements like protein powders, protein bars, caffeinated drinks and powders, creatine, and ephedrine.

Who should take supplements?

For most healthy individuals who eat a variety of foods, dietary supplements are not necessary. Food will always be the preferred source for the nutrients your body needs. No supplement can replace the benefits of a healthy diet. Instead, you need a unique combination of vitamins, minerals, phytonutrients, and other substances.

Still, there are some situations where supplements can be helpful.

  • A woman with heavy menstrual bleeding may need an iron supplement.
  • A pregnant or breastfeeding woman may benefit from taking a supplement containing folate, iron, and calcium.
  • A woman able to or thinking about becoming pregnant should take a folic acid supplement to prevent possible birth defects that can occur before she even knows she’s pregnant.
  • Those with higher risk for vitamin D deficiency–such as individuals with limited milk intake and sunlight exposure–should take additional vitamin D.
  • A person on a very restrictive diet, such as a strict vegan or very low calorie diet, may be missing out on key nutrients and should consider a multivitamin/mineral.
  • Older adults may be advised to supplement calcium and vitamin D as well as vitamin B12.
  • Individuals who have a medical condition that affects how the body absorbs or uses nutrients may need supplementation.
  • Others as indicated by a registered dietitian or health care provider.

Do supplements work?

Sound scientific evidence supports the benefits of some dietary supplements. However, many supplements are lacking good quality research to back their claims. Good research provides data from randomized, placebo-controlled, double-blind studies.

There should be multiple studies, not just one, and several studies should have duplicate results. Testimonials are NOT sufficient evidence to warrant use of a supplement. Unfortunately, supplement manufacturers are not required to conduct research on their products or prove their effectiveness in any way.

Before you decide to take a supplement, do a little research. Look to credible sources such as your pharmacist or health care provider. If you look for information online, make sure you stick to reliable, unbiased websites such as those run by the government or an educational institution. I recommend these four links:

Are supplements safe?

When we hear something described as “herbal” or “all natural,” we automatically assume the product is safe. That isn’t always the case. Just because a supplement is available for purchase, it doesn’t mean it is safe or effective. Many supplements are full of unknowns: unknown benefits; unknown interactions with other foods, medicines, or supplements; undetermined standards; and unknown levels of safety and effectiveness.

It is important to understand that supplements do not undergo the same level of scrutiny as medications. The United States Food and Drug Administration (FDA) has limited authority over supplements. In fact, the FDA does not review supplements for safety or effectiveness before they are marketed to the consumer. Instead, the FDA is only able to remove harmful products from the market.

It is up to the manufacturer to ensure that the supplement’s package label information is accurate, its ingredients are safe, and the declared contents match what’s actually in the container. While many supplement labels are accurate and complete, some aren’t.

Sometimes, the potency or purity may be incorrect or inconsistent. In some cases, the contents listed on the label may not actually be inside the container. In some cases, supplements were tainted with banned substances.

For better peace of mind in the product you are buying, look for the USP (US Pharmacopeia) Verified Mark on product labels. The USP is an independent not-for-profit organization that sets quality standards for strength, quality, purity, and consistency of supplements. It is a voluntary check that supplement manufacturers can choose to go through to provide assurance to the consumer.


Before you decide to take a dietary supplement, try altering your diet instead. And if you’re already healthy, do you really need that supplement? Many lack scientific proof as to their effectiveness. And those supplements that are effective (such as calcium or vitamin D) are meant to be just that– supplements to a healthy diet. Supplements do not and are not intended to replace a healthy diet or medication prescribed by your doctor.

If you are already taking or considering taking a supplement, it’s important to talk to your doctor or pharmacist. There may be food or medication interactions or other cautions that he or she may warn you about. And, unless your pediatrician prescribes them, avoid giving supplements to your child or teen. A healthy lifestyle – including physical activity, eating a wide variety of nutritious foods, and getting enough sleep – will always be the best path to health for most people.

Do you take dietary supplements in addition to living a healthy lifestyle? What’s your favorite? Let us know in the comments below.

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About Sarah Wood

Sarah Wood is a registered dietitian with a Master's Degree in Applied Health Sciences. Currently, she is a Nutrition and Health Education Specialist with the University of Missouri Extension. When taking time for herself, she runs, travels, and creates art.