Are multivitamins right for you?

Q What are the benefits of taking a multivitamin? Should I take one even if I'm healthy?

A About one-third of Americans take multivitamins regularly. Many purchase the supplement because they think it can impact broad health outcomes — help them live longer, decrease cancer risk and reduce cardiovascular disease. Otherwise healthy people also take it to fill gaps in their diets.

I wish it was that straightforward. Though there's some encouraging data on the benefits of multivitamins for healthy adults, the supplement isn't a cure-all.

There have been three main studies looking into whether multivitamins impact important health outcomes, all of which had private and public support, including from supplement companies:

■ A French study of about 13,000 adults between ages 35 and 60 found an improvement in cancer risk and mortality in men, but not women, after 7½ years of daily supplementation.

■ Another study investigated more than 14,000 U.S. male physicians age 50 or older and showed that multivitamin use for a median of about 11 years was associated with an eight per cent reduction in cancer, though there was no difference in mortality.

■ A study called COSMOS examining multivitamin use over a median of about 3½ years in more than 21,000 older adults found no improvement for men or women in cancer risk, mortality or cardiovascular disease.

Taking a multivitamin daily is generally regarded as safe. But because there isn't enough evidence of benefits for healthy adults, the United States Preventive Services Task Force does not recommend it.

IS IT BETTER TO EAT HEALTHY OR TAKE VITAMINS?

Many people have studied the health benefits of supplementing particular nutrient gaps with a pill — for example, magnesium, which is popular as a supplement and a common feature of many multivitamins.

Studies consistently find that magnesium supplementation is insufficient to achieve the benefits that come with a diet high in magnesium. This is likely because of numerous other health benefits that accompany a balanced diet that are not easily distilled to one — or even a handful — of nutrients taken out of their original forms.

DO MULTIVITAMINS HELP COGNITION?

A large study published in 2023 derived from the COSMOS database found that people taking a multivitamin for a year performed better on an immediate word recall test. In this test, participants read 20 unique unrelated words several times in a row, then were asked to read a new list of 20 words as a distraction, before being asked to recall as many words as possible from the first list. The study authors concluded that multivitamin supplementation had the effect of improving age-related memory changes on this test by about 3.1 years.

WHO SHOULD TAKE A MULTIVITAMIN?

There are a few scenarios where we know multivitamins are important:

■ People with nutritional deficits: This could include people with alcohol use disorder or elderly people living in longterm-care facilities who may have poor fruit and vegetable intake. Other people with specific nutritional deficits, such as vitamin B12 deficiency among vegans, could also reasonably take a multivitamin daily to target their deficiency if a multivitamin contains an appropriate per cent daily value.

■ People who are pregnant or breastfeeding. In this case, a multivitamin containing 400 to 800 mg of folic acid should be taken as directed.

HOW SHOULD I CHOOSE THE BEST MULTIVITAMIN FOR ME?

Generally, it makes most sense to pick a vitamin that targets your sex and age group. Multivitamins targeted at younger women tend to contain higher amounts of folic acid (in case of pregnancy) and iron, which is often low because of losses due to menstruation. If you're someone who takes supplements, read the labels carefully; you don't want to overdo it on any nutrient.

WHAT I WANT MY PATIENTS TO KNOW

Putting anything into our bodies involves a risk-benefit calculation. Many people feel that taking a multivitamin is better than nothing and that the risks are extremely low. While I agree with at least the second part of that reasoning, in the bigger picture, the harm may come less from the multivitamin itself than from what we as health-care providers and society fail to address more fundamentally. When an otherwise healthy patient tells me about their multivitamin, I use that as a starting point to explore what nutrients they may be worried they're not getting through their meals and ways we can support them to eat a more balanced diet.