Beta-carotene supplementation decreases leukocyte superoxide dismutase activity and serum glutathione peroxidase concentration in humans.

The effects of a 30 mg/day beta-carotene supplement for 60 days on blood cell and serum antioxidant enzymes and selenium concentrations were examined in healthy adults. Serum beta-carotene concentrations increased significantly (P < 0.05) in response to supplementation.