Dietary Supplements: What You Need to Know

When it comes to dietary supplements, make sure you know the facts before you buy.


More than half of American adults take dietary supplements—oral products containing at least one vitamin, mineral, herb or other botanical, amino acid, or enzyme—in the belief it will help them stay healthy, sleep better, lose weight, boost energy, and more. While there are cases in which some supplements can be beneficial to health, these products can also be ineffective or even harmful, so it’s important to know the facts before you choose.

Take Charge!

If you’re thinking of taking a dietary supplement, keep these points in mind:

  • Be aware. Taking dietary supplements can involve risks. The FDA does not review safety and effectiveness of individual supplements.
  • Ask your healthcare provider. Always ask about benefits and risks that are specific to your personal health issues and other medications or supplements you are taking.
  • Eat well. Supplements do not replace a healthy diet and lifestyle. Diet is the best source of nutrients.
  • Look for a third-party stamp. Companies like (CL), NSF International, United States Pharmacopeia (USP), and Banned Substances Control Group (BSCG) test for quality.
  • Protect yourself from COVID-19. While maintaining adequate levels of nutrients may help the body fight infection, extra intake is not proven to be helpful. Get vaccinated, mask up, and practice social distancing.

Effectiveness. For people with a nutrient deficiency due to a genetic condition, or those with severely restricted dietary intake or issues impacting nutrient absorption, dietary supplements can be helpful. For individuals who are not deficient in a particular nutrient, little data confirm health benefits to taking additional amounts. A few nutrients that do show promise include vitamin A for vision protection, calcium for bone health, and omega-3 fatty acids for brain health, but significant questions remain. The majority of studies are observational, which means they show an association between taking a supplement and a particular health outcome, but do not prove cause and effect.

Supplements do not replace a healthy dietary pattern. A recent study by Tufts researchers found that higher intake of certain vitamins and minerals, such as vitamin A, vitamin K, magnesium, zinc, and copper was associated with lower risk of death, but only when these nutrients came from food, not supplements. Researchers also reported that excess nutrient intake could have adverse effects.

Safety. Even though they are sold without a prescription, there can be serious risks involved with taking dietary supplements. Many ingredients that have biological effects can be dangerous when taken in high doses. Additionally, some supplements interact with prescription medications or other supplements, which can lead to adverse effects. It’s important to consult with your healthcare provider before starting a dietary supplement, no matter how innocuous it may seem.

Manufacturers of supplements are responsible for ensuring the safety and quality of their products, but they don’t have to prove the supplements are safe, nor do they have to prove the accuracy of claims on product labels. Some dietary supplements have been found to contain unsafe ingredients as well as ingredients not listed on the label. Supplements advertised for bodybuilding, weight loss, and sexual enhancement are highest risk.

Being a Savvy Consumer. The world of dietary supplements is one of “buyer beware.” Remember that claims that seem too good to be true likely are. Be especially wary of claims that a dietary supplement helps prevent or cure disease (these statements are legally allowed only on FDA-approved medications.)

Always seek out information using noncommercial internet sources rather than relying on marketing from sellers (see Resources). Scan labels for third-party certification stamps from companies such as (CL), NSF International, United States Pharmacopeia (USP), and Banned Substances Control Group (BSCG). This means the product has been tested for quality by a company not involved in the production or sales of the supplement.

Supplements are not meant to be a quick-fix or a substitute for prescription medications or an unhealthy diet or lifestyle. Eating well, being physically active, and taking medications as prescribed are all most of us need to do to support our health.


Sales of dietary supplements marketed for immune health have risen since the emergence of COVID-19 in the hopes that these products may prevent infection, or at least help reduce disease severity. We talked to Simin Meydani, DVM, PhD, director of the Nutritional Immunology Team at the Jean Mayer USDA Human Nutrition Research Center on Aging, to get the latest on this important topic.

Editor: Dr. Meydani, where does this idea come from that specific nutrients may help fight viruses, and COVID-19 in particular?

Dr. Meydani: There are two points at which we can fight viruses like COVID-19. The first is the point of entry, where a strong immune response fights against infection. The second is after infection, when, in COVID-19, a huge inflammatory reaction referred to as a cytokine storm leads to damage in the lungs and other parts of body, which is the cause of severe illness and death. Nutrients from the foods we eat are intricately involved in regulating both immune function and inflammatory responses in the body. This fact has led to a lot of interest in dietary supplements as a way to fight COVID-19.

Several vitamins and minerals—including vitamin C, vitamin D, vitamin E,
and zinc—are known to be important for proper immune function, and inadequate levels of these nutrients in the body can increase susceptibility to infections. Additionally, antioxidants such as vitamins E and C, quercetin, and phenolic compounds could play a role in controlling the cytokine storm. But we need to see if this potential translates to actually helping with the disease.

Editor: What is the research showing us so far?

Dr. Meydani: At this point, we have some suggestive evidence, but not enough to go out and make recommendations that people take dietary supplements, let alone determine how much they should take.

Low serum levels of vitamin D and zinc are associated with worse outcomes in people with COVID-19, but it’s important to recognize that association is not causality. We don’t know if the low levels contribute to the disease or the disease contributes to the low levels.

There have been a few studies that have been done with supplementation of vitamin D, vitamin C, and zinc, alone or in combination, and results are mixed. One small study found vitamin D supplementation to be effective, but other studies have not supported that earlier finding. Studies so far have been small and have had issues with design and so forth.

The upshot is, researchers are not ready yet to rule dietary supplements out in terms of their effectiveness, but we are also not ready to recommend any supplements to reduce illness and death from COVID-19.

Editor: Is there evidence that there may be additional benefits if we go beyond current recommended intake levels of helpful nutrients?

Dr. Meydani: This is not a case of “more is better.” While adequate intake of nutrients is important, we don’t have enough research to say that intake of any of these nutrients or food components above recommended levels is beneficial in controlling this disease. Importantly, intake of dietary supplements—such as zinc and vitamins D—beyond the upper limits of recommendations has been associated with adverse health effects.

Editor: How does one ensure adequate nutrient levels?

Dr. Meydani: Getting adequate dietary intake of essential nutrients from foods is the best way to ensure ideal nutrient status in healthy individuals. Many key immune- and inflammation-controlling compounds are found in fruits and vegetables, so make sure you eat plenty of these.

If you have a condition affecting absorption, your healthcare provider may recommend specific supplements. Older adults are also at increased risk for deficiency of certain nutrients. For example, 20 to 30 percent of adults over 65 have low zinc levels, and evidence from our own studies suggests older adults may need more vitamin E than is currently recommended in order to maintain optimal immune response. (We found 200 milligrams a day is best for optimal immune and inflammatory responses—although this has not been tested with COVID-19 specifically.)

With few exceptions, a healthy dietary pattern will supply all the nutrients most people need.

Editor: Can you summarize for our readers your advice on taking dietary supplements to combat COVID-19?

Dr. Meydani: I believe the best advice is for everyone to make sure you have the adequate levels of essential nutrients in your diet.

There is no concrete evidence at this time to recommend going above and beyond these adequate levels by adding dietary supplements unless you are told by a doctor you are deficient.



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