Adults who drink more than three half-pint glasses of milk a day may be at higher risk of breaking bones and even of dying, warns new research.
The study found a high milk intake in women and men is not accompanied by a lower risk of fracture and instead may be associated with a higher rate of death.
Researchers, whose study was published in the British Medical Journal, suggest the findings may be explained by the high levels of lactose and galactose sugar in milk.
However, they cautioned their study can only show an association and cannot prove cause and effect.
The researchers say the results “should be interpreted cautiously” and further studies are needed before any firm conclusions or dietary recommendations can be made.
A diet rich in milk products is currently promoted to reduce the likelihood of brittle bone fractures.
However, previous research looking at the importance of milk for the prevention of fractures and the influence on mortality rates show conflicting results.
Researchers in Sweden, led by Professor Karl Michaelsson, set out to examine whether high milk intake may increase “oxidative stress” which, in turn, affects the risk of mortality and fracture.
Two large Swedish groups of more than 61,000 women, aged 39 to 74, and more than 45,000 men, aged 45 to 79, completed “food frequency” questionnaires for 96 common foods including milk, yoghurt and cheese.
Lifestyle information, weight and height were collated and factors such as education level and marital status were also taken into account. National registers were used to track fracture and mortality rates.
Women were tracked for an average of 20 years, during which time no reduction in fracture risk with higher milk consumption was observed. And women who drank more than three glasses of milk a day (680ml or 1.43 pints) had a higher risk of death than women who drank less than one glass of milk a day (average 60ml).
Men were tracked for an average of 11 years, and also demonstrated a higher risk of death with higher milk consumption, although this was less pronounced than in women.
The researchers concluded that there may be a link between the lactose and galactose content of milk and risk.
Dr Michaelsson said: “Our results may question the validity of recommendations to consume high amounts of milk to prevent fragility fractures.
“The results should, however, be interpreted cautiously given the observational design of our study. The findings merit independent replication before they can be used for dietary recommendations.”
Professor Mary Schooling, of City University of New York, said the new findings raise a fascinating possibility about the potential harms of milk.
However, she stressed that diet is difficult to assess precisely and she reinforced the message that these findings should be interpreted cautiously.
Prof Schooling added: “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.”