Should we be worried about drinking milk?

Angelina Jolie, David Beckham and Elton John have all sported milk moustaches to persuade us to drink enough to keep our bones strong.

Milk contains a range of nutrients, including calcium, phosphorous, magnesium and vitamin B12. Government guidelines say adults need 700mg of calcium a day (a 200ml glass of semi-skimmed milk contains 247mg). The Dairy Council lists the benefits of milk as reducing the risks of osteoporosis, breast cancer and heart disease. Milk, it continues, is the only drink other than water that dentists recommend between meals.

However, recent research threatens milk’s goody two shoes image. A Swedish study reported in the British Medical Journal followed more than 61,000 women and 45,000 men for between 13 and 22 years. The researchers found that drinking more than one glass of milk a day was associated with an increase in deaths and fractures in women and a borderline rise in the risk for men of dying from heart disease.

Women who drank two glasses compared with one were 21% more likely to die during the study period, and this rose to 93% for three or more glasses. (Over the 22 years of the study, a quarter of the women died in total.) They were 16% more likely to have a fracture if they drank two or more glasses a day. There was no extra risk for men. So is it a myth that milk makes bones stronger? And can a few glasses of milk a day do more harm than good?

The solution

This study doesn’t provide proof of causation. The authors propose a mechanism for milk’s harmful effects – its high content of D-galactose (galactose is a sugar), which is shown to cause oxidative stress, inflammation and ageing in animal studies. An intake of fermented dairy products didn’t seem to have any downside, and women (but not men) who ate lots of yoghurt and cheese (which contain less D-galactose than milk) actually reduced their risk of fractures or dying.

It is advisable to treat this study with caution for many reasons. The study was conducted in Sweden, where the environment is different from that in the UK, and vitamin A is added to milk there. The study also relied on people self-reporting how much they were drinking, which isn’t always reliable – especially as milk is also consumed in cereals and cooking.

It can also be hard for researchers to take into account all the other factors that increase someone’s risk of dying or breaking their bones. Nutritional guidelines are unlikely to change in the short term until there is more direct evidence on the long-term effects of liberal milk drinking. The phrase “more research is needed” was invented for questions such as this.