Beta-carotene is a pigment found in plants like sweet potatoes, carrots, leafy greens, etc.[1] It is also available as a dietary supplement. Because beta-carotene is a provitamin A carotenoid, it is converted to vitamin A in the intestine when ingested.[1]
Observational studies show that higher dietary intake of beta-carotene is associated with improved cognitive function[2] and a lower incidence of depression,[3] osteoporosis,[4] and bone fractures.[5] Observational studies also show that a higher beta-carotene concentration in the blood is associated with improved cognitive function[2] and a lower incidence of metabolic syndrome.[6] However, these studies use cross-sectional or cohort study designs, and beta-carotene intake data is estimated from food frequency questionnaires. Furthermore, randomized controlled trials examining many of these outcomes are lacking, making it difficult to draw firm conclusions. That said, evidence from randomized controlled trials shows that supplementation with beta-carotene has no beneficial effect on cognitive function,[2] nor does it have any effect on the risk of cardiovascular disease, the risk of cancer, or associated mortality.[7][8][9] Some evidence even shows that supplementation with beta-carotene might increase the risk of lung cancer, particularly in smokers.[8][9] Consequently, the causal effects of beta-carotene intake on disease risk/prevention are mixed, and high-quality dose-response randomized controlled trials will be needed before firm conclusions can be made.