Vitamin A and osteoporosis

Vitamin A and osteoporosis
It has long been known that high doses of vitamin A can cause liver abnormalities. Now researchers are examining an excess intake of vitamin A as a potential risk factor for osteoporosis. Animal, human, and laboratory research suggests an association between greater vitamin A intake and weaker bones. The large doses of vitamin A may impair the ability of vitamin D to promote calcium absorption. The high doses are associated with reduced bone mineral density and increased risk of hip fracture. There is no evidence of an association between beta-carotene intake, especially from fruits and vegetables, and increased risk of osteoporosis.
In the 1970s, FDA considered writing regulations for some mega-dose vitamin products because of their potential health risks. The supplement industry waged a lobbying effort against the FDA’s attempt, and the Proxmire Vitamin and Mineral Amendment of 1976 expressly prohibited the FDA from establishing maximum limits on the potency of any vitamin or mineral.
“Osteoporosis, a disorder characterized by porous and weak bones, is a serious health problem for more than 10 million Americans, 80% of whom are women. Another 18 million Americans have decreased bone density which precedes the development of osteoporosis. Many factors increase the risk for developing osteoporosis, including being female, thin, inactive, at advanced age, and having a family history of osteoporosis. An inadequate dietary intake of calcium, cigarette smoking, and excessive intake of alcohol also increase the risk.” http://ods.od.nih.gov/factsheets/vitamina.asp#h7.