Ferreting out beta-carotene's toxicity.

While it's hard to get toxic quantities of beta-carotene from eating fruits and vegetables, one study found that high-dose supplements might be harmful. They appear to increase a smoker's risk of lung cancer (SN: 1/27/96, p. 55). A 6-month study in ferrets, which process this carotenoid much as humans do, now indicates that excess beta-carotene oxidizes. The resulting metabolites unleash a toxic double whammy.

Xiang-Dong Wang of the Agriculture Department's Human Nutrition Research Center on Aging in Boston and his coworkers supplemented the animals' diet with beta-carotene in an amount comparable to that used in the earlier human cancer study. Some animals were also exposed to cigarette smoke.

In the lung, beta-carotene's metabolites destroyed retinoic acid, a vitamin-derived compound that suppresses cancer growth. The metabolites also activated a protein that spurs cell division, Wang's group reports in the Jan. 6 Journal of the National Cancer Institute. While the untreated ferrets had healthy lungs, those exposed to the supplements underwent precancerous changes. The lung damage was most prevalent in the animals who were also exposed to the smoke.