• Health

Want to Build Endurance? Cut Back on Vitamin C and E Supplements

2 minute read

Athletes who want to make sure they’re doing whatever they can to be at their peak rely on supplements help and even boost their training. A quick Google search of “athletes + vitamin E” shows a plethora of claims about the benefits of the vitamin for physical activity and recovery.

But a new study published in The Journal of Physiology says that advice may be misguided. Researchers at the Norwegian School of Sport Sciences report that vitamin E and vitamin C supplements may actually hamper endurance by interfering with exercise-induced cell signaling in the muscles.

MORE: Exercise Keeps Muscles Young, Even in Elderly Heart Patients

For 11 weeks, the researchers monitored 54 young, healthy men and women and randomly assigned them to consume either 1000mg of vitamin C and 235mg vitamin E, which is the amount found in most supplements, or a placebo. The volunteers then participated in an endurance training program that involved running and other activities for three to four exercise sessions each week. All the participants took fitness tests and provided blood samples and muscle biopsies.

The supplements did not seem to impact how much oxygen the muscles used, but only those on placebo showed higher levels of mitochondrial proteins, which help to build new muscle and provide cells with energy. The researchers believe that the supplements blunted the participants’ ability to build up muscle endurance.

What does that mean for fans of Vitamins C and E? Mike Gleeson, a professor of exercise biochemistry at Loughborough University told the BBC that the data don’t necessarily mean that the supplements are harming athletes.”The bottom line is studies show changes in the ability to adapt to exercise could be impaired by high-dose vitamins, but until there are studies showing them affecting athletic performance, people shouldn’t be worried.” But they probably shouldn’t be relying on the pills to see them through a marathon run, either.

More Must-Reads from TIME

Contact us at letters@time.com