by Amanda Smith, Associate Editor
Most developed nations have established recommendations for their citizens' daily intakes across a variety of food groups; milk and dairy products are often included for their contribution to a balanced diet. A diet rich in milk products is promoted to reduce the likelihood of osteoporotic fractures. But, could a consumption of a high dairy diet actually have the opposite effect?
Using an observational study, a group of Swedish researchers attempted to examine whether high milk consumption is associated with mortality and fractures in women and men. The study used two cohorts: one composed of 61,433 women, ages 39 to 74; the second with 45,339 men, ages 45 to 79. To measure intake of different foods, participants were administered food frequency questionnaires.
At follow-up 20 years later, 15,541 women had died and 17,252 had a fracture. The male cohort was re-evaluated 11 years later. At this time, 10,112 men had died and 5,066 had a fracture.
Compared to those who consumed less than a glass of milk a day, women who consumed three or more glasses of milk each day had 1.93 times the risk of mortality. With greater levels of milk consumption, a reduced risk for fractures or hip fractures was not observed. High milk intake, to a lesser degree, was also associated with a higher mortality risk among men (1.10).
Surprisingly, the opposite effect was observed with cheese and fermented dairy product consumption. For each serving of these dairy products, the rate of mortality and fractures was reduced by 10 to 15 percent. The researchers suggest this may be due to milk's D-galactose (a by-product of lactose breakdown) content.
Due to the observational study design, though, the authors recommend a cautious interpretation of the results. Christopher Labos, M.D., in the Montreal Gazette, seconded this opinion. Yet, in typical fashion, the mainstream media seems to have ignored this caution.
Labos notes that one particular flaw inherent in this study method is that people tend to modify their eating habits to more closely align with what they think researchers want to hear. He also posed the following question: "Is there a factor that is more common among milk drinkers and also more common among people who develop fractures?" Osteoporosis, he noted, is a confounder; the authors of the study did not adjust their results for osteoporosis or bone mineral density.
