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Ask Tufts Experts January 2010 Issue

Q: Since calcium and vitamin D strengthen bones and vitamin A weakens bones, why is all reducedfat milk fortified with both vitamin A and vitamin D? And why is whole milk not?

Answer :  Robert M. Russell, MD, professor emeritus at Tufts’ Friedman School and former director of the Jean Mayer USDA Human Nutrition Research Center on Aging, explains: “It is true that in animals and man vitamin A in very high (toxic) doses can cause bone demineralization and a weakening of bones. Also, there have been some epidemiological studies that have shown a relationship between vitamin A intakes above one-and-a-half to two times the Recommended Dietary Allowance (RDA) and lower bone density, but this is far from proven. There are many other published studies that have not shown this relationship. At any rate, the vitamin A fortification level of skim and low-fat milk is low and safe (150 micrograms in a cup—whereas the RDA for an adult male is 900 micrograms per day). Low-fat and skim milk are required by the FDA to be fortified at this level, as the vitamin A is lost from the milk when the fat content is lowered (the baby is thrown out with the bathwater, so to speak). Whole milk still has plenty of fat and vitamin A content, which is absorbed well due to the fat that it travels with.”

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