Nearly one in three Americans takes a daily multivitamins, with the primary motivation being maintaining or improving health. Studying the effectiveness of multivitamins in the “real world” is complicated by the healthy user effect – those that take vitamins typically eat healthier, exercise more, and smoke less. There is also the sick user effect which may play a factor – in that patients with a diagnosed disease may increase their multivitamin intake because of the perceived benefits.
A new study looks at mortality risk with daily multivitamin use by analyzing three different US populations where there were repeat assessments of use over an extended period, with the tracking of health-related outcomes. This is a massive study of over 390,000 adults where 164,000 deaths were reported.
The Study
This was not a new clinical trial. It was led by Erikka Loftfield and researchers at the National Institutes of Health’s National Cancer Institute and was published on June 26, 2024, in JAMA Network Open. Participants in this analysis were drawn from the National Institutes of Health–AARP Diet and Health Study (NIH-AARP) cohort (initially, 550,596 AARP members aged 50-71); the PLCO Cancer Screening Trial cohort (65,577 participants, aged 55-74); and the Agricultural Health Study (AHS) cohort (57,333 participants aged 18+). After data quality exclusions, other exclusions included those with extreme calorie intake or those with chronic diseases. The final population available for the analysis was 390,124 adults, with trial entry as early as 1993! The median age was 61 and the cohort was 55% male.
In all three trials, participants were asked at initiation and in follow-up about their supplement use. Those that answered “Yes” were asked about frequency of multivitamin use using predefined categories. Categories of multivitamin use were harmonized into three groups: nonusers, non-daily users, and daily users of multivitamins.
As I noted above, there are many potential confounders which the authors attempted to harmonize across studies, including age, sex, race/ethnicity, education levels, smoking status/intensity, BMI, marital status, physical activity, alcohol intake, coffee intake, other supplement use, Healthy Eating Index and family history of cancer.
Participants were followed from baseline until date of death, loss to follow-up, or the closure of the study period. Cause specific mortality was determined from death certificates. Baseline results from the three different studies were similar, so the pooled analysis formed the basis of the overall conclusions. While confounding was minimized, because this was observational data, it’s possible that there are unmeasured/unadjusted confounders that were not addressed.
Results
In the three cohorts, multivitamin daily users vs nonusers were comparable with a few differences:
Participants who used multivitamins were more likely to use individual supplements, have lower BMI and better diets compared to non-users. Multivitamin use didn’t vary significantly by race/ethnicity or family history of cancer.
As for the effectiveness? Daily multivitamin use was associated with a higher mortality risk compared to non-users (Hazard ratio 1.04, 95% confidence interval 1.02-1.07). That is, mortality was 4% higher among multivitamin users. There were no differences in mortality when looking at heart disease, cancer, and cerebrovascular mortality:
No Justification for Daily Multivitamins
There’s no question that vitamins play a critical role in health. Supplementation is justified and evidence-based in some circumstances, such as folate supplementation in pregnancy. Supplementation is not always beneficial though – look to the harms caused by beta-carotene supplements or vitamin E supplements. The benefits of multivitamin supplements have also been questioned for years. While many take multivitamins as “insurance” against a diet which may not be optimal, there is a lack of evidence showing that general multivitamins provide any meaningful benefits.
Given how regularly Americans take multivitamins, it’s important to understand their health effects. This massive study with over 20 years of follow-up has showed that there is no clear justification for routine use of multivitamins in healthy adults. Rather, multivitamins users appear to be slightly more likely to die than their non-user counterparts. An accompanying editorial points out that mortality effects, like this research studied, may miss other health-related benefits such as age-related macular degeneration with specific supplements. While this is true, it reinforces the need for targeted, science-based supplementation when the evidence supports it, rather than indiscriminate multivitamins.
The supplement industry has put a tremendous con over consumers, promoting the idea that vitamin and mineral supplements are beneficial to your health, and that more=better. None of this has been shown definitively to be true when it comes to longevity. It is now very evident that multivitamins as form of dietary “insurance” is a strategy that is at best, useless, and at at worst, causing reducing life expectancy.