Leslie M. Klevay
Nutritional epidemiologists with the Harvard School of Public Health have studied more than 75,000 nurses for 12 years hoping to identify the causes of chronic diseases such as osteoporosis. In a recent article, they report "that data do not support the hypothesis that higher consumption of milk or other food sources of calcium by adult women protects against hip or forearm fractures." Careful reading of the article reveals that the best statistical association indicates the opposite effect: the higher the intake of dairy calcium (milk, cheese, yogurt, etc.), the higher the hip fracture risk. They suggest that some other characteristic of the dairy foods may have contributed to the elevated risk.
Epidemiologists are always careful to note that statistical association does not prove cause; associations may be the result of chance. One wonders whether or not there may be a reasonable biological explanation for this association: diets high in milk contribute to osteoporosis. I learned in medical school that milk was an excellent food, lacking only copper, iron and vitamin D. Milk has been fortified with vitamin D for more than 50 years.
Recently, I uncovered some interesting and important old articles while preparing to speak at the recent International Meeting on Copper in Ravello, Italy. Numerous articles on children deficient in copper reveal osteoporosis characterized by relatively transparent bones on x-ray. A text of nutritional pathology published in 1958 contains picture of dogs with deformed feet caused by copper deficiency. Two other research groups published similar pictures of deficient pigs. Some of the classical experiments on copper deficiency were done by feeding the animals milk diets.
We at the Grand Forks Human Nutrition Research Center and others have found microscopic evidence of bone disease in mildly copper deficient animals. We have measured bone strength in copper deficient animals and found the bone to be weak.
Some medical scientists examining this evidence may wonder whether or not copper supplements may benefit women who have osteoporosis. Randomized trials in California and Northern Ireland have confirmed the benefit of supplements containing copper.
Because the U.S. diet is generally low in copper, and copper deficiency can produce bone disease, it seems time to consider the possibility that these low-copper diets may contribute to osteoporosis. I propose that the higher fracture rate in nurses who consume more dairy calcium may have been from a concomitantly lower copper intake.