It’s seen as one of life’s more wholesome tipples. But drinking milk in large quantities may not be as good for general health and bones as we thought, according to a study of thousands of Swedish people. However, other researchers have criticised the study for raising more questions than it answers. The study, which tracked 61,433 women aged 39 to 74 over 20 years, and 45,339 men of similar age for 11 years, found that the more cows milk people drank, the more likely they were to die or experience a bone fracture during the study period. The risks were especially pronounced for women, a group advised to drink milk to help avoid bone fractures that result from osteoporosis. Women who said they drank three or more glasses of milk a day had almost double the chance of dying during the study period as those who reported drinking only one. A glass is defined as a 200 millilitre serving. They also had a 16 per cent higher chance of getting a bone fracture anywhere in the body. The risks for men were lower, with those drinking three glasses having a 10 per cent higher chance of dying during the study. The researchers accounted for the age and BMI of the participants, the amount of physical activity they did, their education and whether they had ever smoked. Although Swedes are known to drink more milk than most other nations, only 10 per cent of the people in the study drank three glasses or more a day. “They’re provocative findings, I know, but these are the facts,” says Karl Michaëlsson of Uppsala University in Sweden, who led the team. “The amount is important, so if you drink only small amounts, there’s no problem.” However, he says the study only shows an association, and it doesn’t prove that milk is causing the effects. A randomised controlled trial would be needed to tease that out, he adds. If the results are backed up, Michaëlsson says the most likely explanation is damaging inflammation caused by galactose, a breakdown product of lactose, the main sugar in milk. In a separate group of people, the team found that the more milk that people drink, the more inflammatory molecules were present in their urine. What’s more, women who reported eating a lot of cheese and yoghurt had a lower chance of fracturing a bone or dying during the study than women who ate low amounts of the dairy products. This supports Michaëlsson’s inflammation hypothesis because yoghurt and cheese contain much less lactose and galactose than milk. Despite the findings, the UK’s dietary advice remains unchanged. “Public Health England recommends that milk and dairy products such as cheese and yoghurt are sources of protein and calcium as part of a health balanced diet,” says Louis Levy of Public Health England. “The findings of this study would not lead us to change this advice.” Overall, says Levy, the evidence is mixed on consumption of dairy products and health risks. Some studies suggest dairy consumption has a small protective effect when it comes to heart disease and stroke. Other work provides inconsistent evidence of a relationship between milk consumption and adult-onset diabetes. “The authors themselves advise caution in interpreting the results, and are not recommending that anyone stops drinking milk or eating dairy products,” Levy says. Catherine Collins, a dietician at St George’s Hospital NHS Trust, points out that participants weren’t asked to report what kind of exercise they took, just how much. This matters, because different kinds of exercise have different effects on bone strength. What’s more, when the subjects of the study reported the fractures they got, low-impact injuries such as falls weren’t distinguished from high-impact injuries such as those sustained during a car accident. Without clarification, Collins says, the additional fracture risk in avid milk drinkers could merely reflect poor driving skills.
New Scientist, 28 October 2014 ;http://www.newscientist.com/ ;