Do people who work out need a multivitamin?

Short answer

Not if you eat enough. Taking one for 3-8 months did not change performance, and it did not lower the risk of death. When you eat little on a diet or lack something like vitamin D, filling just that gap works.

Do people who work out need a multivitamin?
'More training → need more vitamins → one pill boosts performance' — does this formula hold?
A common belief: hard training drains vitamins, so you need a multivitamin. We checked whether one extra pill really improves performance and health.
Performance did not improve
Records did not budge after 3 to 8 months
22 people took a high-dose multivitamin for 90 days, and their endurance and strength were no different from placebo. In a trial where 30 people took it for 3 months each way, 15 km run times did not change. 82 people who took it for 7-8 months showed almost no change in performance either.
Why no effect?
They already got enough from food
The 82-person trial checked that participants met the daily recommended intake from food alone, and the 22-person trial involved well-nourished people. Adding more to a body that already has enough did not raise performance.
What about health?
It did not help people live longer
An analysis pooling 84 studies with 739,803 people found multivitamins lowered cancer cases by 7%, but did not reduce heart disease or death. A study following 390,124 people for up to 27 years found daily users had no lower risk of death, and in the early years their risk was 4% higher.
Flip side: high doses cut training gains
High-dose vitamins C and E held back muscle growth
When people lifted while taking lots of vitamins C and E, biceps strength in 32 people over 10 weeks and upper-body muscle in 23 people over 10 weeks grew less than with placebo. In 34 people aged 60-81 over 12 weeks, lean mass (muscle and everything except fat) rose 1.4%, short of 3.9% on placebo.
What you need is the one thing you lack
30% were short on vitamin D
An analysis pooling 5,456 people found 30% were low in vitamin D. 10 people who cut 5% of their body weight in 3 weeks ate thiamin, magnesium and zinc at or below recommended levels. The International Society of Sports Nutrition (2026) also concluded supplements are for shortfalls or when food intake falls short.
Bottom line: one multivitamin won't raise performance
Filling only what you lack is enough
For people who eat enough, a multivitamin added neither performance nor years of life. High-dose antioxidant vitamins even held back muscle growth. When you eat little on a diet, or a shortfall like low vitamin D is confirmed, filling just that gap works.