Serum retinoic acid levels in patients with resected benign and malignant colonic neoplasias on beta-carotene supplementation.

To determine whether patients with colon cancer metabolize beta-carotene differently from benign colon polyp patients, a normal control group (n = 13) and groups of resected colon polyp patients (n = 29) or resected colon cancer patients (Dukes A and B1, n = 21) were supplemented with placebo or beta-carotene (30 mg/day) taken with their morning meals for three months. Serum samples at zero and three months of the study were analyzed blindly for retinoic acid and beta-carotene. The results showed that beta-carotene levels in the serum of colon polyp and colon cancer groups were 8- to 12-fold higher than in the untreated control or the placebo-treated groups. The benign polyp subjects (n = 17) receiving beta-carotene showed a significant rise in serum trans-retinoic acid at three months compared with Time 0. The trans-retinoic acid values from the colon cancer group receiving beta-carotene (n = 11) or placebo (n = 10) were significantly lower than the values from the beta-carotene-supplemented colon polyp group. It appears that trans-retinoic acid levels in response to beta-carotene supplementation are different between treated cancer and benign patients because of different body demands for retinoic acid.