Dietary Supplements: What You Need to Know Family Doctor Logo

What is a dietary supplement?

A dietary supplement is a vitamin, mineral, or herb that you take to improve your health or wellness. These supplements are generally not intended to cure or treat diseases or medical conditions, unless they have been approved for a health claim by the U.S. Food & Drug Administration (FDA).

Vitamins, Minerals, and Dietary Supplements

Vitamins and minerals, also called micronutrients, nourish your body and help to keep you healthy. You can get most of your micronutrients by eating a variety of foods in your daily diet. Getting your micronutrients through food ensures that your body is able to absorb them properly.

If you don’t eat a variety of healthy foods, such as fruits, vegetables, lean meats and fish, you may not be getting all the micronutrients your body needs. A multivitamin or supplement may be able to help. Other people who may benefit from taking a multivitamin or supplement include:

  • Vegetarians who do not eat any animal products (vegans)
  • Women who are pregnant or trying to get pregnant
  • Women who are breastfeeding
  • Women who experience heavy menstrual periods
  • Women who have gone through menopause
  • People who have had gastric bypass surgery for weight loss
  • People who have a medical condition that affects the way the body digests food, such as gastrointestinal disease, lactose intolerance, or food allergies
  • People who have diseases of the stomach, liver, pancreas, or gall bladder

There is no current evidence that shows that taking multivitamins can help reduce your risk of cancer or cardiovascular disease.

What might be missing?

According to the U.S. Department of Agriculture (USDA), adult Americans may not get enough of the following nutrients:

NutrientRecommended Daily Amount (RDA)
Calcium1,000 milligrams (mg)
Potassium4,700 mg
Fiber25 grams (g) for women
38 g for men
Magnesium320 mg for women
420 mg for men
Vitamin A2,310 international units (IU) for women
3,000 IU for men
Vitamin C75 mg for women
90 mg for men
Vitamin E15 mg

Other Dietary Supplements

Hundreds of dietary supplements are available. They are advertised to treat just about any symptom. However, trustworthy evidence to support these advertising claims is often missing.

Some of the most popular supplements include glucosamine and chondroitin sulfate, probiotics, digestive enzymes, echinacea, coenzyme Q10 (CoQ10), garlic, ginkgo biloba, ginseng, kava, melatonin, phytoestrogens (such as black cohosh, dong quai and soy), saw palmetto, and St. John’s wort.

Nutrient Recommended Daily Amount (RDA)
Calcium1,000 mg
1,200 mg – Women >51 years
1,200 mg – Men >70 years
Folate400 mcg
Iron8 mg
18 mg – Women (19-50 years)
Vitamin B122.4 mcg
Vitamin D600 IU
800 IU – Men and women >70 years

Tips for Taking Supplements

  • Talk to your doctor before you begin taking any dietary supplement.
  • Do not take more than the dosage recommended on the label, unless your doctor tells you to.
  • Read the ingredient list to make sure you know what else is in the supplement.
  • Just because a supplement is advertised as “natural” doesn’t mean it’s safe.
  • Be sure your doctor knows about all the supplements you take – they can interact with some medicines.

How do I know if I should take a dietary supplement?

If you are concerned that you are not getting enough vitamins and minerals in your diet, talk to your doctor about ways to get the micronutrients you need. Depending on your overall health and the vitamins or minerals your diet lacks, your doctor might suggest a dietary supplement. If you are interested in taking another type of supplement, talk to your doctor about why you want to take it and what you hope it will do for you.

While foods that are rich in vitamin E and beta-carotene are very healthy and help reduce cancer risk, the U.S. Preventive Services Task Force (USPSTF) and the American Academy of Family Physicians (AAFP) recommend against taking vitamin E or beta-carotene for the prevention of cardiovascular disease. People who smoke or have a high risk for lung cancer should not take beta-carotene because it can increase the risk of lung cancer.

Your doctor can also help you figure out if a dietary supplement will interact with any medical conditions you have, or any prescription or over-the-counter (OTC) medicine you are taking. Supplements can also cause problems with cancer treatments or surgery, including bleeding and problems with anesthesia.

How safe are supplements?

All manufacturers of prescription and OTC medicines that are regulated by the U.S. FDA follow high-quality standards when making these products.

Some manufacturers of dietary supplements follow the U.S. Pharmacopeial (USP) Convention quality standards. Those manufacturers of dietary supplements who follow the USP quality standards volunteer to have their supplements tested for quality and purity by an outside company before they are sold. These supplements often display additional quality credentials on their labels, such as “USP Verified” or “ Approved Quality.”

Choose your supplements carefully, and talk to your family doctor and/or your pharmacist if you have questions.

Vitamins, minerals, and dietary supplements are generally considered safe as long as they are not used in excessive amounts. This is particularly true for the fat-soluble vitamins A and E. Check the recommended daily allowance (if there is one) and be careful not to take too much.

Although herbs have been taken for many years, some herbal supplements may not be pure. They might contain other unlisted ingredients that could make you sick. Sometimes they contain drugs that aren’t listed on the label, such as steroids, or estrogens. Some of these products may even contain toxic (poisonous) substances, such as arsenic, mercury, lead, and pesticides. If dangerous ingredients are discovered after the supplement has been sold, the supplement must be recalled.

You should never take more of any dietary supplement than the recommended dosage on the label, unless your doctor tells you to do so. Taking too much of a vitamin, mineral or herbal supplement can cause unwanted or dangerous side effects.

Questions to Ask Your Doctor

  • How do I know if I need a dietary supplement?
  • How do I know what dosage should I take?
  • What dietary supplements might be beneficial for me?
  • Is a vitamin considered a dietary supplement?
  • Can dietary supplements interact with food or medicines that I’m already taking?
  • Can dietary supplements cause side effects?
  • Can the dietary supplements I take interfere with lab results?
  • How often should I take a dietary supplement?
  • Are dietary supplements safe?
  • Are “natural” dietary supplements safer?
  • Is there anyone who should avoid taking dietary supplements?
  • There are so many dietary supplements available at the store. How do I pick the right one for me?

Download a copy of these questions to ask your doctor. (PDF 1 page)