Many of your patients probably turn to dietary supplements and special diets to try to avoid diseases like diabetes and its associated eye problems. But if they’re eating yellow vegetables because of the antioxidant beta-carotene, you might want to temper their expectations.

Researchers from Brigham and Women’s Hospital in Boston compared a group of 10,756 healthy men randomly assigned to 50 mg of beta-carotene every other day to a control group of 10,712 men given a placebo. After 12 years of beta-carotene supplementation, 396 (3.7%) of the men in the treatment group developed type 2 diabetes compared with 402 (3.8%) of the men in the control group.

The authors note that "Beta-carotene supplementation had no effect on the risk of type 2 diabetes in this randomized trial of 12 years’ duration.

"The results of our study, however, should not be interpreted as completely refuting the findings of observational studies that increased intake of vegetables that are rich in carotenoids and other antioxidants may decrease the risk of type 2 diabetes. Our trial could not exclude the possibility that some carotenoids or nutrients other than beta-carotene are responsible for the observed association."