Multivitamins’ effects on lifespan: Growing data for the ongoing debate

A recent cohort study tracking nearly 400,000 generally healthy adults over 20 years found that daily multivitamin (MV) intake isn’t associated with a longer life.^[] However, one in three adults in the US take MV without clear evidence the daily supplement boosts longevity.

The researchers noted that in 2022, the US Preventive Services Task Force found insufficient evidence for determining MV benefits and harms. Studies on MV benefits haven’t been very clear over the years, the researchers say—mostly due to study heterogeneity and the "healthy user effect" or "sick user effect."

More harm than good?

For example, one study published in the American Journal of Epidemiology found “no clear decrease or increase in mortality from all causes, cardiovascular disease, or cancer and in morbidity from overall or major cancers among multivitamin supplement users.”^[]

On the other hand, an article in Clinical Interventions in Aging found that specific vitamins could potentially cause harm: “Much of the enthusiasm for the use of vitamin or mineral supplements to prevent disease or increase longevity results from the belief that supplementation is harmless. However, serious adverse events have been reported.”^[]

Which vitamin is the least useful?

To find some clarity, the researchers pulled data from three prospective cohort studies in the US. Participants took part in one of the following: the National Institutes of Health–AARP Diet and Health Study, the Lung; the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial; or the Agricultural Health Study.^[] The goal was to estimate the association of MV use with mortality risk, while also accounting for any confounding variables.

The studies each included baseline and follow-up MV use. They also used data from up to 27 years of follow-up, along with data from any potential confounding variables. The use of MV was self-reported. All of the participants were generally healthy US adults with no history of cancer or chronic disease. 

Analysis took place between June 2022 to April 2024. 40.9% of participants said they were never smokers (11% of daily MV users, vs 13% of nonusers, were current smokers), while 40.3% said they were college-educated.  

The researchers found a correlation between gender, education, and MV use: “Among daily MV users, 49.3% and 42.0% were female and college-educated, compared with 39.3% and 37.9% among nonusers, respectively.”

Of the 390,124 participants (median age 61.5, 55.4% male), there were 164,762 deaths during the follow-up period, with almost 50,000 deaths due to cancer, just over 35,000 deaths due to heart diseases, and almost 93,000 deaths due to cerebrovascular diseases.

Mortality impacts

These findings are not surprising, says Cheng-Han Chen, MD, a board-certified interventional cardiologist and Medical Director of the Structural Heart Program at MemorialCare Saddleback Medical Center in Laguna Hills, CA. “There has never been a clear benefit,” Dr. Chen says, “and this current and large analysis again shows no mortality benefit.” 

The findings don’t mean that patients should assume MV explicitly causes harm, he says. It’s not entirely clear why there's a 4% increase in mortality risk, but to gain validity these numbers would have to be reproduced in other studies, he adds. 

“Daily multivitamins aren't going to kill you…but [physicians] do not routinely recommend daily MV use simply because many decades of data haven't found [any] benefit. The only thing the MV affects is the wallet.”

Advice for the clinic

Dr. Chen recommends that physicians tell their patients to focus on a healthy, balanced diet with lots of whole grains, fruits, and vegetables, and less saturated fat, salt, sugar, and processed food. “If you want to be healthy, the healthiest form of a nutrient is in the food vs a processed pill made in a factory,” he says.

He also says that patients should be aware that too much of a good thing can be harmful. For example, Dr. Chen says, “You might build up too much iron or niacin from a daily [MV].” He notes that some supplements touted as miracles haven’t been proven to work. In other words, good marketing can play a big role in why patients are scooping these products off the shelves. 

It’s not surprising, then, that the JAMA Network Open study found that some patients are doubting MV efficacy. In fact, MV use decreased by 6% from 1999 to 2011, which may reflect, “growing uncertainty about the effectiveness of MV supplementation for preventing disease, following the publication of several studies that reported no benefit of MV use for reducing risk of cardiovascular disease, cancer, or mortality.”