Calcium in adulthood: no proof of fracture reduction
Posted by medconsumers on October 5, 1997
Celebrity “milk mustache” ads have successfully sold the idea that adults should increase their calcium intake. And ads for calcium supplements have long been a staple for magazines and TV shows with primarily female audiences. Lost in these promotional activities, however, is the fact that researchers have failed to prove that increasing calcium intake in adulthood will prevent fractures in old age. The latest “thumbs down” finding comes from the storied Nurses Health Study, which showed that higher consumption of milk or other food sources of calcium by adult women offers no protection against hip or forearm fracture (American Journal of Public Health, June 1997). At least three other published studies have produced the same result.
Calcium is essential for building bone mass in youth, but the investigators noted that the extent to which adult milk consumption helps to maintain bone structure is unknown. Seven published studies have proven that calcium supplementation will retard bone loss in adult women. The ultimate goal, however, is reducing the rate of hip fracture, which is precisely where the evidence has been inconsistent. Some studies say yes; others say no. For the latest study, Diane Feskanich, ScD., and colleagues at the Harvard School of Public Health, explored data from the Nurses Health Study in order to determine whether higher calcium intake from food sources reduces fracture risk. To avoid confusion over the role of calcium supplements, the investigators eliminated all the nurses who had taken them. That left more than 77,000 women in 11 states who were between the ages of 30 and 55 years in 1980 when they began filling out extensive questionnaires about their health habits and medical conditions. Thereafter, follow-up questionnaires were mailed every two years.
Dr. Feskanich and colleagues concluded, “These data suggest that more frequent milk consumption and higher dietary calcium intakes in middle-aged and older women do not provide any substantial protection against hip or forearm fractures. Increased consumption of milk and dairy foods, which are sources of both calcium and vitamin D, have been found to improve calcium balance and to lower rates of bone loss in the spine and femoral neck [the long bone of the thigh as it meets the hip] in clinical trials with adult women. However, it is possible that the observed improvements were transient effects of bone remodeling that may not be sustained in the long-term.” Worse, the investigators found that, “Women consuming greater amounts of calcium from dairy foods had modest but significantly increased risks of hip fracture while no increase in fracture risk was observed for the same levels of calcium from nondairy sources.”
What about calcium supplements? The numerous studies showing reduced bone loss with calcium supplementation usually last about two or three years. As for the more important question of hip fracture, the news isnt any better than it is for dietary calcium. After a 6.6 year follow-up of nearly 10,000 white women over the age of 65, Dr. R.G. Cumming and colleagues at the University of Sydney, Australia, concluded: “Current use of calcium supplements was associated with increased risk of hip and vertebral fractures; current use of Tums antacid tablets was associated with increased risk of fractures of the proximal humerus [upper arm bone]. There was no evidence of a protective effect of vitamin D supplements.” (American Journal of Epidemiology, 15 May 1997)
So if increasing dietary and/or supplemental calcium intake doesnt reduce your chances of having a hip fracture in old age, why do most of us think it will? One possible answer was provided unintentionally by a recent AMA press briefing on nutrition, notably funded by an educational grant from the National Dairy Council. In the press kit was a paper from yet another physician-led organization, the AMAs Council on Scientific Affairs, telling adults to increase intake of calcium-rich foods. (In 1994, the National Institutes of Health advised all adults to increase calcium intake to over 1,000 mg daily.)
The National Dairy Council has long been a funding source for nutrition education, and now that doctors have discovered the importance of nutrition, the Council sponsors educational events like the AMA briefing. Afterwards, one reporter from a leading women’s magazine conceded privately that her magazine’s advertising revenues from calcium supplements and dairy industry ads would prevent her from writing an article such as this one youve just been reading.
Maryann Napoli, Center for Medical Consumers(c)