Dietary Supplements: Helpful, Harmful, or Harmless??>

Dietary Supplements: Helpful, Harmful, or Harmless?

by Tim Gower

Americans’ obsession with dietary supplements continues to grow, but so does evidence that many vitamin and mineral supplements do little to protect or improve our health. Several recent studies have added to the dismal overall track record for dietary supplements when they’re tested in rigorous clinical trials. Here’s a look at the latest findings.

Cardiovascular supplements

Getting certain nutrients directly from the food you eat can help reduce your risk of death—and other health problems—but getting the nutrients from dietary supplements isn’t the same, according to a study published in July 2019 in the Annals of Internal Medicine. The extensive review found that just two in 16 nutritional supplements recommended for preventing early death and cardiovascular disease offered any protection, and even those two, omega-3 fatty acids and folic acid, had uncertain evidence.

Researchers from Johns Hopkins, Mayo Clinic, West Virginia University, and other medical institutions reviewed studies that investigated the association between nutritional supplements and cardiovascular disease (which includes heart disease and stroke) among nearly 1 million people. They concluded that the following nutritional supplements had no positive effect on longevity or cardiovascular health:

  • Vitamins A, C, D, E
  • Vitamin B complex, vitamin B6, vitamin B3 (niacin)
  • Multivitamins
  • Antioxidants
  • Calcium
  • Iron
  • Selenium
  • Beta-carotene

Among the study’s other findings, albeit with low-quality evidence:

  • Omega-3 fatty acid and folate supplements might reduce heart attack and stroke risk, respectively.
  • Vitamin D combined with calcium offers no benefit but might do harm by slightly increasing stroke risk.

An earlier study, published in April 2019 in the Annals of Internal Medicine, had similar thumbs-down findings for supplements. In that study, researchers from Tufts University in Boston assessed data from more than 27,000 U.S. adults ages 20 and older from the National Health and Nutrition Examination Survey and the National Death Index. They looked at the association between dietary supplement use and death from all causes, such as heart disease and cancer.

They found that getting the right amount of vitamin A, vitamin K, copper, magnesium, and zinc was associated with a reduced risk of premature death, but only if the source of the nutrients was food.Overall, the results showed that if adults aren’t getting the nutrients they need from food, getting them from dietary supplements doesn’t lower the risk of early death.


One in three adults takes a daily multivitamin, the most popular dietary supplement in the United States. Unfortunately, multivitamins won’t cut the average person’s risk for heart attacks or strokes, according to a Johns Hopkins–led analysis in Circulation: Cardiovascular Quality and Outcomes in 2018.

Researchers analyzed 18 observational and clinical trials involving more than 2 million people over an average of 12 years. The researchers concluded that multivitamins and mineral supplements don’t reduce the risk of heart attacks, strokes, or other cardiovascular-related deaths.

The Hopkins analysis builds on past studies that came to similar conclusions. In 2014, the U.S. Preventive Services Task Force (USPSTF) reported that there wasn’t enough evidence to support taking multivitamins or most other vitamin and mineral supplements to prevent cardiovascular disease or cancer. Multivitamin formulas vary greatly, so even if there were benefits (or harms), it would be difficult to know which components and dosages were responsible.

Related: Should You Still Take That Multi?

If multivitamins have an effect—good or bad—it is likely to be small or may occur in just a small subgroup of people. As it is, the weight of evidence suggests that multivitamins provide little or no benefit for well-nourished people, who ironically are the ones who tend to take supplements. Those who would be most likely to benefit from supplementation—that is, people who are truly malnourished—are least likely to take them.

Best Food Sources of Nutrients

The best source of the vitamins and minerals you need for your body is food, not supplements. Here are some nutrient-rich foods to keep stocked in your kitchen.

Vitamin D

One striking recent fall from grace in the supplement world is vitamin D. In the last decade, testing for vitamin D deficiency and sales of supplements of the nutrient increased 100-fold. Originally recommended primarily to help strengthen bones, vitamin D drew scientific interest for its potential to reduce cardiovascular disease and cancer.

Several studies published in 2019 have dampened enthusiasm for vitamin D’s potential as a super-supplement. Most notably:

  • The Vitamin D and Omega-3 Trial (VITAL), which included 25,871 adults ages 50 and older, found that taking 2,000 international units (IUs) of vitamin D daily for about five years did not reduce the risk for cardiovascular disease or breast, colorectal, or prostate cancers. Results were reported in January in The New England Journal of Medicine.
  • An analysis of 21 randomized clinical trials that involved 83,291 people found no evidence that vitamin D is associated with a reduced risk of cardiovascular disease or premature death. The analysis was published in JAMA Cardiology in June.

The findings of VITAL should slow the vitamin D bandwagon. But, the results are hardly the last word. Other clinical trials are underway. The VITAL researchers are continuing to follow the participants’ incidence of cardiovascular disease and cancer.

Vitamin D with calcium

Doctors sometimes recommend vitamin D combined with calcium supplements to help prevent age-related bone loss, but in 2018, the USPSTF announced there’s no evidence that vitamin D alone or withcalcium is associated with reduced risk of fractures in adults without osteoporosis, a prior fracture, or a vitamin D deficiency. However, some critics point out that the USPSTF focused on low doses of vitamin D and that higher amounts could prove protective.

It’s better to get calcium from food than from supplements because foods naturally rich in calcium supply other nutrients essential for bones and general health. If you don’t eat calcium-rich foods often, though, ask your doctor whether you need a calcium supplement. If so, don’t exceed 1,000 to 1,200 milligrams of supplemental calcium.But getting the daily recommended intake of calcium (1,000 mg for men ages 51 to 70, and 1,200 mg for women over 50 and men over 70) from your diet is best.

Can’t Hurt, Might Help? Don’t Be So Sure

An example of this common fallacy is a study in JAMA Network Open, which found that high intakes of vitamins B6 and B12 were associated with increased risk of hip fractures.

What to do

Vitamins, minerals, and other nutrients are essential for a healthy body, but you’re unlikely to gain protection against disease by consuming supplements in high doses. Although there’s little evidence that supplements prevent disease in the general population, specific groups may benefit.

You may need a multivitamin or other nutritional supplement if you:

  • Are frail or elderly and unable to eat sufficient amounts of food, perhaps due to an illness or a poor appetite
  • Are vegan, have a food allergy, have undergone weight-loss surgery, or are on a restricted diet
  • Have a medical condition, such as cancer, anemia, or celiac disease, that causes nutritional deficiencies
  • Are diagnosed with or at elevated risk of a chronic illness, such as age-related macular degeneration, and you may benefit from high doses of specific supplements

If you currently take a supplement, ask yourself why you’re taking it. If you can’t give yourself a clear and specific answer, you’d be well advised to consult with your doctor about it. And it’s always a good idea to consult your doctor or a dietitian for guidance if you’re thinking about starting a supplement. He or she can identify any nutritional gaps you may have and make recommendations specific to your situation.

This article first appeared in UC Berkeley Health After 50.

Also see Dietary Supplements: We Can Do Better.