From Mens Health (even though its specifically about women):
According to a 2002 Harvard Medical School study of 72,000 women, those who consumed between 4,300 international units (IU) and 6,600 IU a day of vitamin A had a 43 percent higher risk of hip fracture than those who consumed 1,700 IU or less. The risk was greater in women who got even more than 6,600 IU. Only one kind of vitamin A retinol, was linked to weaker bones. It’s found in animal foods (dairy, liver, eggs, etc.)
Beta-carotene, which the body converts to vitamin A, is found in fruits and vegetables. It doesn’t increase the risk of hip fractures. Our PowerVites multi vitamins contains 100% Beta carotene.
The vitamin A in nutritional supplements can come from retinol (often called vitamin A palmitate or acetate), from beta-carotene, or from a combination of the two. (Check the nutritional supplements labels. Some simply list vitamin A, which isn’t very useful. But many brands of nutritional supplements also disclose what percentage of their vitamin A comes from beta- carotene, if so, the rest is retinol). To protect bones, limit to no more than 5,000 IU of retinol. But even less would be better, since people also get some vitamin A from their food. This limit is especially important for women (so far, no studies have been done on men’s bones and vitamin A). Roche Vitamins, a major manufacturer of vitamin A, says that many of the nutritional supplements vitamin-makers it supplies have agreed to lower their retinol levels to 2,500 IU
The National Academy recommends 10,000 IU “upper level” (UL) for retinol, which is the highest safe intake. The UL is based on evidence that more vitamin A may cause liver abnormalities and, if consumed by women of childbearing age, birth defects. Beta-carotene doesn’t cause those problems. Limit yourself to 15,000 IU because too much beta-carotene may increase the risk of lung cancer in smokers. (Beta-carotene from foods is safe).
