Vitamin A: New Research Finds Bones Benefit From Less Retinol
Vitamin A hasn’t been in the forefront of nutrition concerns in recent years. Vitamins C and E and folic acid have garnered more attention. But vitamin A is back in the news, and it’s not all good.
Vitamin A is essential for keeping your eyesight keen, your skin silky smooth and your immune system in tip-top working order. Bit scientists have long known that too much A can accumulate in the liver, causing problems. Only recently have researchers uncovered a link between excessive vitamin A—specifically retinol—and weak bones.
How Real the Risk of Too Little? A frank deficiency of vitamin A—and the resulting night blindness—is rare in the U.S., thanks to fortification of such foods as milk and margarine. But even today, people who eat very limited diets and don’t take a daily multi are vulnerable, if only for a borderline deficiency. And because vitamin A is a fat-soluble vitamin, anyone with a condition that causes chronic fat malabsorption may also be at risk for a deficiency, as the vitamin is lost with the fat.
Accumulating A. Excess vitamin A is stored in body fat and in the liver as a reserve for future use. Handy, but dangerous. Continued storage can lead to toxic buildup if excessive vitamin A is consumed regularly, causing dry itchy skin, hair loss, fatigue, loss of appetite and—the most serious—liver problems
But this toxicity is only a problem with “pre-formed” vitamin A—or retinol—the active form of the vitamin found in animal foods, fortified foods and supplements. Certain carotenoids—specifically alpha-carotene, beta-carotene and beta-cryptoxanthin—are plant-derived precursors that can be converted to vitamin A.
Yet they don’t pose the same toxicity risk, because the body converts only as much as it needs. PowerVites contains the good beta-carotene.
Bone of Contention. While adequate vitamin A is necessary for bone growth, too much retinol may be bad for your bones. This is a real problem for older people, who seem to lose the ability to metabolize retinol properly with age, making vitamin A hang around in the liver even longer
In a 30-year Swedish study published last year, researchers found that men with the highest blood levels of retinol had seven times the number of fractures as those with the lowest levels. This backs up earlier findings from Harvard’s Nurses’ Health Study in which women who reported the highest intakes of vitamin A (at least 6,600 International Units a day for 18 years) had nearly double the risk of hip fractures as those with the lowest levels. This backs up earlier findings from Harvard’s Nurses’ Health Study in which women who reported the highest intakes of vitamin A (at least 6,600 International Units a day for 18 years) had nearly double the risk of hip fractures as those with the lowest intakes (less than 1,650 IU). Studies have found no similar adverse effect from carotenoids; plant sources provide A with no worry of excess. However, not everyone is convinced of the latest retinol research.
John Hathcock, Ph.D., of the Council for Responsible Nutrition, which represents supplement manufacturers, cites other data with conflicting results. One study, based on nutrient intakes from the most recent government nutrition survey, found no link between a high vitamin A intake and bone density problems. Diane Feskanich, D.Sc., the Nurses’ Health Study lead researcher, argues, “Most studies have shown an association between vitamin A intake and [poor] bone density.”
Vitamin A in Foods
(Ranked from highest to lowest)