Conclusion
For generally well-nourished adults, routine multivitamin use is not well supported as a way to prevent cardiovascular disease or cancer. A U.S. Preventive Services Task Force (USPSTF) review and related studies broadly agree on this point.
Targeted supplementation can still help when a specific nutrient deficiency is actually present, but that is a different question from taking a multivitamin as a general practice.
How much does it help?
The USPSTF review found that most large trials testing multivitamins for primary prevention of cardiovascular disease or cancer showed no statistically meaningful difference versus placebo.
Several large trials, including Physicians' Health Study II, have tested this question over the years without showing a clear reduction in cardiovascular events overall. Some trials reported small differences in cancer incidence in specific subgroups, but the overall pattern is not consistent.
What the research shows
The evidence base includes a USPSTF systematic review pooling several large clinical trials, along with expert commentary building on those results. Most participants were generally well-nourished adults.
Because the studied populations already had adequate nutrition, added benefit from supplementation is structurally harder to detect, which is one limitation noted in this literature.
Cautions
- If a clear nutrient deficiency is present, checking and addressing that specific nutrient is preferable to a general multivitamin
- Some vitamins and minerals carry risks at high intake levels
- People with existing health conditions or who are pregnant should check with a physician before starting
A simple analogy
Adding fuel to a tank that is already full does not extend how far a car can go. For adults with adequate nutrition, a multivitamin appears to work in a similar way.