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Q: I recently read about a Swedish study that showed vitamin A at higher levels can increase the risk of bone fractures. Can you shed some light on acceptable levels and types of vitamin A?
A: Many human and animal studies suggest that excessive vitamin A intake weakens bone and increases the risk of osteoporosis.
The study of 2,300 Swedish men (New England Journal of Medicine) found that those with the highest blood levels of vitamin A were seven times more likely to suffer bone fractures than those with the lowest vitamin A levels.
The study authors suggest that current amounts of vitamin A in supplements and vitamin A-fortified foods might be too high and should be reassessed.
Looking at the multivitamin product you take is useful in understanding vitamin A. It provides vitamin A in two forms: retinol palmitate and beta-carotene, 7,500 IU of each.
Retinol palmitate is "straight" vitamin A. In contrast, beta-carotene is "pre-vitamin A" that the body converts to vitamin A as needed.
An interesting note: The Swedish study found that beta-carotene levels were not associated with bone fracture risk. This presumably is because the body uses only as much beta-carotene as it needs.
The safe upper level of straight vitamin A is 10,000 IU. The adult recommended daily intake is 3,000 IU for men and 2,300 IU for women.
This latest study suggests it might be best to stay close to the recommended daily intakes. These amounts, the study noted, can be supplied by a healthy diet containing dairy products and fish.
(Richard Harkness is a consultant pharmacist who writes on health care topics. You can write him at 1224 King Henry Drive, Ocean Springs, MS 39564. His e-mail address is firstname.lastname@example.org. Volume of mail prohibits individual replies; selected letters will be answered in his column.)
(c) 2003, The Sun Herald (Biloxi, Miss.). Distributed by Knight Ridder/Tribune News Service.