Milk may not be as good for health as many people believe, according to a new study out of Sweden. Drinking just three glasses a day was linked to an increase in mortality rates and bone fractures in women.
Researchers provided questionnaires to 61,443 women and 45,339 men, asking about dietary choices and habits. Women were aged between 39 and 74 when initially assessed between 1987 and 1990. Men were aged between 45 and 79 in 1997, the same year a follow-up study was conducted on the female subjects.
Bone fractures were reported by 17,252 women within 20 years of their entry to the study, and 15,541 passed away. After an average of 11.2 years, 5,066 men reported fractures, and 10,112 died. Researchers discovered that high levels of milk consumption not only lead to a higher mortality rate among women, but also to a greater number of fractures.
"Because of the high content of lactose in milk, we hypothesized that high consumption of milk may increase oxidative stress, which in turn affects the risk of mortality and fracture," Karl Michaëlsson of the Department of Surgical Sciences at Uppsala University in Sweden, and others, wrote in an article announcing the study.
The mortality rate nearly doubled for women drinking three glasses or more of milk each day, according to researchers. The risk of all forms of bone fractures was also higher among those who drank large quantities of milk.
Michaëlsson and his team believe the consumption of fermented dairy products, such as cheeses and yogurt, would not carry the same potential health risks as milk, due to lower lactose content. The study did not differentiate between different fat levels, classifying skim, low fat and whole milk together in one category.
Galactose, a simple sugar found in milk, could be the active chemical bringing about health risks uncovered in the study.
"That compound might induce oxidative stress and low-grade inflammation, and that type of inflammation can affect mortality and fractures. The funny thing is that if you provide galactose to experimental animals, they will die faster by induction of oxidative stress and inflammation," Michaëlsson said.
It is possible that some of the subjects in the study suspected they were prone to bone fractures, through family history or other means, and compensated by drinking large quantities of milk. This effect, called retrocausality, could be affecting the results of the study.
Despite significant apparent health risks to women, researchers were unable to find any connection between mortality or fractures and milk consumption in men.
Study of milk and possible links to increased mortality in adult women was detailed in the journal BMJ.
