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STUDY: No Link with Vit A and Bone Loss
JOURNAL: Journal of Nutrition 2002;132:1169–72
ABSTRACT: Contrary to a report published earlier this year in the Journal of the American Medical Association, supplementation with moderate amounts of vitamin A does not cause bone loss, according to a study in the Journal of Nutrition (2002;132:1169–72).
COMMENTARY: In the new study, 80 healthy men between the ages of 18 and 58 years were given a vitamin A supplement (25,000 IU per day) or placebo for six weeks. Blood tests taken at the beginning and end of the study revealed that vitamin A supplementation had no effect on various measures of bone breakdown and bone formation.
Thus, at least in the short term, taking a moderate amount of vitamin A is unlikely to promote bone loss.
Previous studies showed that increasing vitamin A intake is associated with an increased risk of hip fracture; however, the relevance of those studies is questionable. The main sources of vitamin A in the diet are vitamin A-fortified foods such as margarine, sugary breakfast cereals, and milk and circumstantial evidence suggests that some or all of these foods can promote the development of osteoporosis for reasons unrelated to their vitamin A content. If that is the case, then vitamin A was a victim of “guilt by association.”
Although taking too much vitamin A can cause a wide range of adverse effects (including neurological disease, liver damage, and even death), bone loss has not been mentioned as a consequence of chronic vitamin A poisoning.
Studies suggest that a safe level of intake of vitamin A is 25,000 IU per day for most healthy adults and 15,000 IU per day for individuals over the age of 65. Larger amounts, which are used by some doctors to treat acne, some cancers, menstrual irregularities, or other problems, should be taken only with medical supervision. Early warning signs of vitamin A excess include headaches, joint pain, muscle aches, bone pain, dry skin, and hair loss. These signs disappear if the vitamin is discontinued.
Preliminary research suggests that pregnant women should not take more than 10,000 IU per day, though not all studies agree on this point. Although the body converts beta-carotene into vitamin A, taking large amounts of beta-carotene does not lead to vitamin A toxicity. That is because there is a limit to the amount of beta-carotene that can be converted to vitamin A.