Americans spend billions of dollars on supplements each year, and roughly 1 in 3 adults report taking a multivitamin. But there is a debate about whether this helps promote good health.

A team of researchers wanted to assess how a daily multivitamin may influence cognitive aging and memory. They tracked about 3,500 older adults who were enrolled in a randomized controlled trial. One group of participants took a placebo, and another group took a Silver Centrum multivitamin, for three years. The participants also took tests, administered online, to evaluate memory.

At the end of the first year, people taking a multivitamin showed improvements in the ability to recall words. Participants were given lists of words — some related, some not — and asked to remember as many as possible. (List-learning tests assess a person's ability to store and retrieve information.)

People taking the multivitamin were able to recall about a quarter more words, which translates into remembering just a few more words, compared to the placebo group.

"We estimate that the effect of the multivitamin intervention improved memory performance above placebo by the equivalent of 3.1 years of age-related memory change," the authors write in their paper, which was published this week in the American Journal of Clinical Nutrition. And the authors point to a sustained benefit.

"This is intriguing," says Dr. Jeffrey Linder, chief of general internal medicine at Northwestern University Feinberg School of Medicine, who was not involved in the study. But he says the overall effect found in the study was quite small. "It seems like a pretty modest difference," Linder says. And he points out that the multivitamins had no effect on other areas of cognition evaluated in the study, such as executive function, which may be more important measures.

Study author Dr. JoAnn Manson, who is chief of the division of preventive medicine at Brigham and Women's Hospital, says this is not the first study to show benefits from multivitamins. She points to a study published last year in Alzheimer's & Dementia that showed participants who took a daily multivitamin performed better, overall, on global cognitive function on tests measuring story recall, verbal fluency, digit ordering, as well as executive function.

"It is surprising that such a clear signal for benefit in slowing age-related memory loss and cognitive decline was found in the study, " Manson says. "Those receiving the multivitamin did better than those receiving the placebo."

Our bodies and brains require many nutrients for optimal health and efficiency. Manson says if people have deficiencies in these nutrients it may influence memory loss or speed cognitive decline. So, she says taking a multivitamin may help someone prevent a deficiency if they're not getting all the nutrients they need from their diet.

"It's important to highlight that a multivitamin will never be a substitute for a healthy diet," Manson says, since micronutrients are typically better absorbed through foods than through supplements." But it may be a complementary approach or strategy for maintaining cognitive health among older adults," she says.

Linder says he will continue to tell his patients that if they eat a healthy diet they are unlikely to benefit much from a multivitamin. "If you're taking too much of a particular supplement and your body doesn't need it, you're just peeing it out," he says. He wrote an editorial, published in JAMA, arguing that vitamins and supplements could be a waste of money for a lot of people. He argues that we should help people adopt a better pattern of eating.

"Eating a diet that has plenty of fruits and vegetables is associated with longevity and better function and better quality of life," Linder says. There's plenty of research to show a healthy diet is linked to better heart health, and when it comes to protecting cognitive function, "the current thinking is that all of the stuff that's good for your heart is also good for your brain," he says.

When Linder talks to his patients about healthy aging, he focuses on good sleep habits, physical activity and a healthy diet. "My big concern with all of the focus that people have on vitamins is that it's distracting them from things that actually will help them stay healthy," Linder says.

"If someone is taking a multivitamin, I'm not going to tell them to stop," says Dr. R. Sean Morrison, who is a geriatrician at Mount Sinai Health System in New York. But he says he would not encourage the use of multivitamins as a way to protect against memory loss, because he says the effects measured in the studies are not very convincing. "I don't think it's the magic bullet that people are looking for," Morrison says. When talking to his patients, he too focuses on the importance of healthy habits and good social relationships.

The study was funded, in part, by the National Institutes of Health and other grants. The vitamins were provided by Pfizer Inc. and Haleon, the makers of Centrum, the brand of multivitamins taken by participants in the study. The study authors say the funders had "no role" in the study design, analysis or interpretation.