Wed. Jul 24th, 2024

Should I take a multivitamin? Here’s what the science says.

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 over 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 8 percent 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 over 21,000 older adults found no improvement for men or women in cancer risk, mortality or cardiovascular disease. An ancillary study did find that certain aspects of cognition significantly improved for men and women over age 60.

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.

My takeaway? Eating a healthy diet has been well established in multiple large studies to improve numerous health outcomes, from reversing coronary heart disease to reducing cancer risk.

You can’t redeem a poor or unbalanced diet by popping a pill to fill in the nutrient gaps.

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.

This data is encouraging. We likely need additional research to understand more about the extent of this effect and to target the right population. For instance, the people who appeared to benefit most are those with baseline cardiovascular disease. It’s not clear why, but it may be that these patients had micronutrient deficiencies, perhaps related to certain cardiac medications.

Still, studies that have used a more extreme endpoint, like the development of dementia, have not shown a benefit from over-the-counter supplements — something that is associated with a healthy diet. And in the 2023 study, multivitamins did not have a significant impact on other cognitive tests evaluating executive function or new object recognition.

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 long-term-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 percent daily value.
  • People who have undergone bariatric surgery. These patients need to be careful to ensure they are also meeting their calcium as well as iron, copper and zinc goals in their supplementation, as many multivitamins may not contain a full daily value of minerals.
  • People who are pregnant or breastfeeding. In this case, a multivitamin containing 400 to 800 mg of folic acid should be taken as directed by their physician.

How should I choose the best multivitamin for me?

Multivitamins are not regulated as medications by the Food and Drug Administration, so there can be wide variations in what goes into each brand’s formulations.

Typically, they contain some percent daily value of key vitamins and minerals. Some brands may contain 70 percent of the daily value of one such nutrient — say, vitamin C — while others contain 200 percent.

Do you really need 200 percent of the full daily value of vitamin C supplemented if you’re healthy? Few clinical trials exist to give these kinds of specific answers.

But 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.

Participants in the COSMOS trial took a Centrum Silver daily multivitamin containing high values of vitamin D and vitamin B12, which are often found in multivitamins targeting older individuals.

If you’re someone who takes multiple supplements, read the labels carefully; you don’t want to overdo it on any nutrient.

People who smoke should avoid multivitamins that contain over 20 mg a day of beta carotene, as several studies have noted an increased risk of lung cancer in this group.

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.

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