Introduction

Micronutrient deficiencies are widespread. Up to 70% of Americans don’t get enough vitamin D, nearly 50% fall short of their magnesium needs, and 35% have an insufficient intake of calcium.

These deficiencies and insufficiencies ravage our health. Inadequate vitamin D increases mortality risk. A magnesium deficiency can accelerate biological aging. Folate deficiency by itself can produce a level of DNA damage that is equivalent to or in excess of an acute exposure to radiation (although this occurs at levels uncommonly seen in human populations).

Addressing these deficiencies seems to hold a remarkable benefit. For example, correcting vitamin D and magnesium deficiencies can reverse epigenetic aging and protect against DNA damage.

Diet should be the primary source of most of our nutrients, but it can be hard to obtain optimal nutrition through whole-food sources.

In light of this, the benefit of a multivitamin seems clear: the downside is low when you consider the overall benefit of potentially shoring up highly individual minor nutritional deficiencies. And the notion that multivitamins have some benefit is shared by many. Around one third of adults report that they take a multivitamin.

A health investment or expensive urine?

Most people take a multivitamin in hopes of preventing disease and delaying death. If something as simple as a multivitamin can help with either of these goals, it’s worth knowing. But some people will tell you that multivitamins are useless. That they’re just creating more expensive urine, at least for those with a well-balanced diet. But this doesn’t seem to be true.

Multivitamins improve cognition

In addition to the potential benefits of multivitamins for preventing conditions like anemia, neural tube defects, cataract, and osteoporosis, there is convincing evidence from randomized controlled trials that supplementing with a daily multivitamin improves brain health and cognition.

In a 3-year study known as the COSMOS (the COcoa Supplement and Multivitamin Outcomes Study), taking a multivitamin improved cognitive function, memory, and executive function compared to a placebo.

A meta-analysis of three COSMOS substudies concluded something similar: There was clear evidence that multivitamin supplementation improved global cognition and memory—an effect that was estimated to be equivalent to a 2-year reduction in aging!

Multivitamins and mortality

When it comes to major diseases and mortality, the data aren’t as clear or convincing.

• Multivitamins don’t seem to reduce the risk of cardiovascular disease, cancer, or all-cause mortality.
• Multivitamins appear to have no effect on total cancer incidence or several types of cancers including breast, colorectal, prostate, or skin (melanoma), although the risk of lung cancer was 38% lower for participants taking a multivitamin.

These conclusions seem to hinge on a lack of evidence that prevents a balance of the benefits and harms from being determined.

Maybe multivitamins don’t need an overwhelming standard of evidence for a large benefit because the overall evidence that each of us may have individual minor nutritional deficiencies is strong. By taking a multivitamin, we hedge our bets that we can reduce the impact of suboptimal nutrition.

But what if there was even a slim chance multivitamins were actually harmful?

One study published in 2024 asserted this, finding that:

• People who reported taking a multivitamin every day had a 4% increase in all-cause mortality risk and a 6% increase in heart disease mortality risk compared to nonusers.
• Taking a multivitamin less than daily was associated with a 9% increase in all-cause mortality risk compared to nonusers at a 12 year follow-up.
• Taking a multivitamin was not associated with a greater or lower risk for cancer or cerebrovascular disease, nor was it associated with mortality from all-causes or specific causes after 15 years or more of follow-up.

Breaking down the study

Published in JAMA and titled “Multivitamin Use and Mortality Risk in 3 Prospective US Cohorts”, this new study attempted to more rigorously assess the link between multivitamin use and mortality by addressing some of the biases that have been present in previous observational studies, namely, the healthy user bias and the sick user effect.

To control for the sick user effect (the possibility that people who get sick will then start using a multivitamin, making them less healthy than nonusers), any participant who had cardiovascular disease, cancer, diabetes, or kidney disease at baseline was excluded.

In an attempt to control for the healthy user bias (the possibility that people who take multivitamins may have better lifestyle habits than nonusers), the statistical analyses were adjusted for confounding factors like age, sex, education, alcohol and tobacco use, BMI, physical activity, diet quality, family history of cancer, and the use of other supplements.

A total of 390,124 participants were pooled from 3 large prospective cohort studies. The participants were asked at least once whether or not they used a multivitamin and were then separated into one of three groups based on their answer:

• Daily multivitamin users (n=163,307)
• Nondaily multivitamin users (n=47,151)
• Nonusers (n=179,666)

The participants were followed for a median of 23 years, during which deaths from all-causes, heart disease, cancer, and cerebrovascular disease were recorded at two time points: the first 12 years (follow-up number one) and 15 years and beyond (follow-up number two).

Is daily supplementation risky?

During follow-up period number one—people who used multivitamins daily had a 4% greater risk for all-cause mortality than people who never used multivitamins, while people who used multivitamins less than daily had a 9% increase in all-cause mortality. No differences in all-cause mortality were observed during the second follow-up period—which was 15 years or more after the baseline assessment.

Other than heart disease mortality—the rate of which was 6% higher in daily users compared to nonusers during the first 12 years of follow up—there were no significant differences between multivitamin users and nonusers in the risk of dying from heart disease, cancer, or cerebrovascular disease. The same was true for nondaily users vs. nonusers.

In other words, taking a multivitamin wasn’t associated with protection against dying from these diseases, but it wasn’t associated with any harm either.

The researchers also conducted an analysis that included a second assessment in which participants indicated their multivitamin use (on average, 6 years after their baseline assessment). This is important, because it’s a better indicator of multivitamin use over time than a single assessment at baseline—it helps to control for multivitamin use habits that may have changed during the study.

The result? A similar finding to the first analysis: A 4% greater all-cause mortality risk in daily multivitamin users in the first 12 years of follow up and no difference in all-cause or cause-specific mortality at the 15-year and beyond follow up.

One more reason to question these results

The hazard ratios (HRs) for these outcomes were all very close to 1. An HR compares the likelihood of an event (such as heart disease or death) happening in one group compared to another. If the HR is 1, it means the risk is the same in both groups. If the HR is above 1, the risk is higher in the first group; if it's below 1, the risk is lower.

An HR close to 1 means that the risk of the events happening was nearly the same for both multivitamin users and non-users. For example, the hazard ratio of 1.04 for all-cause mortality in daily multivitamin users indicates a very small increase in risk. However, this increase is quite weak, and the confidence interval (1.02–1.07) shows the result is very close to no difference between the groups.

The increased risk is likely due to some as-yet unidentified factors that were different between multivitamin users and nonusers. Or perhaps it was a mere statistical artifact.

Conclusion

All of this probably has you wondering: “Should I take a multivitamin or not?

Overall, most people should take a multivitamin as a means of nutritional insurance and to obtain micronutrients that might be harder to get from food.

If you are currently taking a multivitamin, don’t stop based on the results of one single study. There’s an enormous difference between multivitamins not being tied to improved longevity and multivitamins being tied to reduced longevity. I think this study confirms the former—any emphasis on the latter is just a useless distraction. Multivitamins may be benign, but they’re unlikely to be harmful.

What’s important to remember is that exercise, sleep, and diet are exponentially more important for your longevity whether or not you take a multivitamin. Make sure you have these “low hanging fruit” taken care of before you begin to worry about the smaller—albeit still important—lifestyle inputs. At the end of the day, if you’re worrying about whether taking a multivitamin is shortening your lifespan, you’re worrying about the wrong things.

Don’t let misleading headlines about studies steer you away from what really matters for your health.