Daily supplementation with 1000 mg of vitamin C and 235 mg of vitamin E for 10–12 weeks reduces gains in muscle mass and maximal strength in young, recreationally trained adults undergoing resistance training by blunting redox-sensitive signaling pathways critical for muscle hypertrophy.

When muscles are trained, they produce natural chemical signals called reactive molecules that turn on growth pathways. Taking high doses of vitamin C and E every day removes these signals before they can activate the machinery that builds muscle. This stops the muscle from making new proteins and growing larger, so strength and size gains are smaller.