The bone-strengthening powers of milk have been claimed over and over again in advertisements, pop culture and around the dinner table. But a new study published in the BMJ suggests that the truism may not be true. High milk intake, the study found, doesn't appear to protect against bone fracture and in fact may lead to increased mortality.
Researchers looked at questionnaires from more than 100,000 people in Sweden on their dairy consumption habits. The study, which followed up with many of the participants after 11 to 20 years, found that high milk intake was associated with higher mortality in both men and women, as well as higher bone fracture in women.
"Our results may question the validity of recommendations to consume high amounts of milk to prevent fragility fractures," the study says. However, the authors stress that the study is merely observational and not meant to draw causal conclusions.
One possible explanation the authors give for the results is that high levels of the sugars lactose and galactose in milk may cause bones to undergo changes—like inflammation—that resemble aging, leading to the fractures. In animals, supplementing with galactose has been shown to increase aging processes like inflammation and oxidative stress. Data from the study showing a correlation between reduced fractures and low-lactose milk consumption further supports this claim.
More research is needed, of course. "As milk features in many dietary guidelines and both hip fractures and cardiovascular disease are relatively common among older people, improving the evidence base for dietary recommendations could have substantial benefits for everyone," wrote Mary Schooling, PhD, a professor at the City University of New York, in an accompanying BMJ editorial.