photo of woman taking supplements

Dietary supplements include vitamins, fish oil, herbs, minerals like calcium, and more. And if you take one, you’re not alone. About half of U.S. adults do. But should you?

That’s a question for your doctor or dietitian, says Linda Van Horn, a professor of preventive medicine at Northwestern University.

“I get some concern when I see people take one of these and one of those, just because they’ve read somewhere that a supplement is helpful,” Van Horn says. “Imbalances can easily occur, and you may not be aware of it.”  

Food is the best way to get your vitamins and minerals. But it sometimes can be hard to eat enough fresh veggies, fruits, whole grains, and other healthy options. A multivitamin can be a safe way to boost your nutrients.

Do You Need a Supplement?

Most healthy people don’t need one. But some folks may need extra help, says Jerlyn Jones, a registered dietitian and spokesperson for the Academy of Nutrition and Dietetics. Reasons include if you’re elderly, take certain medicines, or don’t have easy access to healthy food because of income or where you live.

Talk to your doctor if you:

Are or might get pregnant. You may not get enough iron from food, especially if you get morning sickness. And all women who are pregnant, or trying to be, should take folic acid. Prenatal vitamins give you “an extra cushion of safety,” says Van Horn.

Care for a young child. Infants and children may need help getting vitamin D and iron.

Eat a restricted or limited diet. It’s harder to get some nutrients, like vitamin B12 or calcium, if you leave out certain food groups. That may happen if you’re vegan or have a dairy allergy.

Are older than 50. Your body starts to absorb less of vitamins D and B12 as you get older. After you reach middle age, you may need to take extra steps to get enough.

Had gastric bypass surgery. Your gut may not absorb nutrients as well.

Have certain genetic or health conditions. You may have trouble absorbing nutrients if you have:

  • Inflammatory bowel disease (like ulcerative colitis or Crohn’s)
  • Celiac disease
  • Cystic fibrosis
  • Liver disease
  • Cancer
  • An autoimmune disorder (like pernicious anemia)
  • Alcohol dependence 
  • A mutation in certain genes
  • Darker skin (you may absorb less vitamin D)

Possible Deficiencies

If you think that your diet lacks certain vitamins or minerals, your doctor may recommend a blood test to confirm. For example, if you’ve been vegan for a few years, you may want to check your levels of vitamin B12, calcium, and vitamin D.

No matter what kind of diet you follow, tell your doctor if you have these symptoms:

  • Extreme hair loss
  • Bone or joint pain
  • Serious tiredness
  • Irregular heartbeat
  • Vision changes
  • Wounds that heal slowly

Nutritional deficiencies are rare in the U.S., where obesity is a much bigger health issue. But there’s a growing concern that some Americans are falling short in some key nutrients, Jones says. Among the list are:

  • Vitamin D
  • Calcium
  • Potassium
  • Magnesium
  • Iron

Supplements and Safety

Experts agree there’s no harm in taking a multivitamin every day. But if you also eat fortified foods and drinks, you might go over the tolerable upper level (UL) for some nutrients. That can raise your chances of side effects. Some might be mild, like nausea. But others, like bleeding, can be serious.

“At high doses, (supplements) are drugs,” says Donald Boyd, MD, a registered dietitian and assistant professor of medicine at Yale School of Medicine.

Dietary supplements aren’t regulated like medicine. That means there’s no way to know exactly what’s in them.

Always make your doctor aware of any drugs you’re taking.  Some supplements, like St John’s wort and vitamin K, can interfere with how your medicine works. You may bleed more during surgery. Anesthesia may not work the right way.

Certain supplements warrant extra caution. Boyd says they include:

Beta-carotene and vitamin A. High doses may raise the chances of lung cancer if you smoke. If you’re pregnant, vitamin A in retinol form may make it more likely that your baby will have birth defects. 

Antioxidants.  The roles of vitamins C and E in cancer prevention and treatment are still being studied. There is some evidence that high doses may affect certain cancer treatments.

Vitamin B12. Newer supplements have very high doses. You may get side effects like anxiety, dizziness, or headaches if you take too much.

Vitamin D. Too much of this can lead to a buildup of calcium (hypercalcemia). That may give you kidney stones.

Research on Supplements

Certain dietary supplements are proven to help. For example, calcium and vitamin D can lower bone loss and fractures. But many products, including herbs like ginkgo biloba, lack solid evidence for their health claims.

And if any supplement says it can cure dementia or Alzheimer’s disease, don’t believe it

Here’s what research says about some popular options:

Omega-3 fatty acids. Animal research shows that fish oil may promote heart health, help blood flow, and lower inflammation. Research on humans is less clear. But some studies suggest it may:

  • Ease symptoms of rheumatoid arthritis, when taken along with other RA medicine
  • Lower your triglycerides, when taken as a prescription

Research to prove the benefits of omega-3 supplements continues.

Vitamins. These are a good way to fix a nutrient deficiency. But multivitamins aren’t likely to help you live longer or lower your chances of long-term health problems. That includes heart disease, cancer, or diabetes. And there’s no evidence that vitamins can help you think or remember better.

Supplements for age-related eye disease (ARED). A certain mix of antioxidants, zinc, and omega-3 fatty acids may slow down ARED.

Tips on Use and Storage

Always check with your doctor first, especially about how much to take, Jones advises.  Good rules to follow include:

  • Don’t go over your recommended Daily Value (DV) for vitamins and minerals unless your doctor says it’s OK.
  • Multivitamins don’t have 100% of your DV for calcium or magnesium. You may need a separate supplement.
  • Buy brands with USP, NSF, or another third-party “seal of approval.”

It may be easier to remember to take your vitamins if you keep them in your bathroom. But light, moisture, and medicine can make a poor combo. Keep your supplements somewhere cool and dry, such as on your dresser.  

Show Sources


Linda Van Horn, PhD, RD, chief of nutrition; professor, department of preventive medicine, Northwestern University Feinberg School of Medicine.

Donald Boyd, MD, RDN, assistant professor of medicine, Yale School of Medicine.

Jerlyn Jones, RDN, spokesperson, Academy of Nutrition and Dietetics.

FDA: “FDA 101: Dietary Supplements,” “Vitamin and Mineral Chart,” “Watch Out for False Promises About So-Called Alzheimer’s Cures,” “How to Report a Problem with Dietary Supplements.”  

Nutrients: “The Evolving Role of Multivitamin/Multimineral Supplement Use among Adults in the Age of Personalized Nutrition.”

National Center for Complementary and Integrative Health: “Vitamins and Minerals,” “Ginkgo,” “Using Dietary Supplements Wisely.” “Vitamins, Minerals and Supplements: Do You Need to Take Them?” “Is Your Body Trying To Tell You Something? Common Nutrient Inadequacies and Deficiencies.”

National Institutes of Health, Office of Dietary Supplements: “Multivitamin/mineral Supplements,” “Vitamin B12,” “Folate,” “Dietary Supplements: What You Need To Know,” “Omega-3 Fatty Acids,” “Frequently Asked Questions (FAQ)."

Harvard Health Publishing, Harvard Medical School: “Taking too much vitamin D can cloud its benefits and create health risks,” “The complicated relationship between fish oil and heart health.” 

Merck Manual: “Celiac Disease.”

Mayo Clinic: “Vitamin B-12.”

Johns Hopkins Medicine: “Vegan Food Guide,” “Is There Really Any Benefit to Multivitamins?”

Rush University Medical Center: “6 Signs of Nutrient Deficiency.”

American Lung Association: “Antioxidants: Lung Cancer’s Friend or Foe?”

Andrologia: “The excessive use of antioxidant therapy: A possible cause of male infertility?” 

Circulation: “Omega-3 Fatty Acids for the Management of Hypertriglyceridemia: A Science Advisory From the American Heart Association.”

National Eye Institute: “For the Public: What the AREDS Means for You.”

World Journal of Diabetes: “Excess vitamin intake: An unrecognized risk factor for obesity.”