Milk may damage the bones rather than protect them, it is claimed today.
Dairy-rich diets have been thought to reduce the risk of osteoporosis. This is because milk contains nutrients including calcium, phosphorus, and vitamin D.
Some studies have suggested that the equivalent of three or four glasses of milk a day is beneficial.
But milk also contains the sugar D-galactose which has been linked to health problems such as chronic inflammation, and rapid ageing in animals, when consumed regularly.
Now a team from Uppsala University in Sweden, has looked at links between high milk consumption, death rates and fractures in adults.
They used figures on 61,433 women followed for 20 years, and 45,339 men followed for 11 years. In this time, 15,541 women died and 17,252 had a fracture (including 4,259 hip fractures). Among the men, 10,112 died and 5,066 had a fracture (1,166 hip fractures).
For women, drinking three or more glasses of milk a day was linked to a 93% higher risk of death compared with drinking less than one glass a day. Death from all causes was 15% more likely with every daily glass of milk for women, and 3% more likely for men. No protective effect of milk against fracture risk was seen.
In further smaller studies, higher milk intake was linked to greater oxidative stress and a biomarker of inflammation.
The researchers admit their findings need to be treated with caution. It is possible that people at the greatest risk of disease drink more milk – and different kinds of high-fat and low-fat milk products could have different effects.
Writing in The BMJ, Professor Karl Michaelsson and colleagues say that "High milk intake was associated with higher mortality in one cohort of women and in another cohort of men, and with higher fracture incidence in women."
But they add: "A cautious interpretation of the results is recommended."
Michaelsson, K. et al. Milk intake and risk of mortality and fractures in women and men: cohort study. BMJ 29 October 2014 doi: 10.1136/bmj.g6015 [abstract]
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