Short-term vitamin A supplementation does not affect bone turnover in men.

Limited data in humans and animals indicate that excess vitamin A stimulates bone resorption and inhibits bone formation, effects that over time might lead to bone loss and fracture. Thus, it is possible that vitamin A supplementation is a currently unrecognized risk factor for the development of osteoporosis. To further evaluate this possibility, a prospective, randomized, single-blind study of vitamin A supplementation was conducted in 80 healthy men age 18-58 y.