The Claim: Lutein, a plant antioxidant, is critical for maintaining good vision and may even help keep brains healthy as they age.

The Verdict: A large government study found that a daily cocktail of dietary supplements including lutein reduced the risk of a chronic eye disease progressing to an advanced stage. Other studies suggest that lutein can improve vision in healthy adults and improve cognition with age, but scientists say more research is needed.

Lutein...