A new study suggests that consuming too much milk lowers the risk of bone fractures among men and women, but increases their risk of death due to oxidative stress.
Oxidative stress is a disturbance between the production of free radicals and the body's ability to neutralize their harmful effects through antioxidants. The body's ability to produce antioxidants depends on genes and environmental factors such as smoking and diet. Oxidative stress has been linked to many diseases such as cancer and Alzheimer's disease, as well as body aging.
Researchers from Uppsala University in Sweden led by Professor Karl Michaëlsson initiated a study to determine if there is a link between high consumption of milk and oxidative stress. The study involved 61,433 women between ages 39 and 74, and 45,339 men with ages 45 to 79 who all answered questionnaires asking them of their food consumption including dairy products.
The researchers followed the participants in an average of 20 years and looked at national registers to monitor fracture and mortality rates. During the follow-up period, 25 percent of the women died while 28 percent had a fracture. Males, on the other hand, who were monitored for an average of 11 years, came close in terms of death risk at 22 percent, though fracture risk was lower compared to women at 11 percent.
Further analysis showed that drinking three glasses of milk daily did not reduce the women's fracture risk but instead increased their risk of dying, compared to those who drank only a glass of milk per day.
The researchers concluded that high consumption of milk is linked to oxidative stress and inflammation, but the risk can be reduced by drinking fermented milk with low lactose content especially for women. Michaëlsson believes that increased risk might be due to the types of sugar found in milk but admitted that further study is needed to prove it.
"As milk consumption may rise globally with economic development and increasing consumption of animal source foods, the role of milk and mortality needs to be established definitively now," said Prof. Mary Schooling of City University of New York in a news release. She wrote an editorial about the research.
Meanwhile, other experts seemed to disagree with the results of the research and warned people not to avoid milk as a calcium source.
"There may be another factor causing the increased mortality and fracture rate in women. Milk is a convenient source of calcium as well as many other vitamins and minerals. One such study is insufficient to base public health decisions on," Gaynor Bussell, a public health nutritionist, told The Telegraph.
Further details of the study were published in the British Medical Journal.
