How many of us were told as children to drink our milk because it would give us strong bones?

The idea does make some sense. Milk contains calcium. Calcium is known to improve bone mineral density.

But demonstrating a definitive link between the consumption of milk and the possession of strong bones is harder than it sounds. The ideal study would take two large groups of people and randomly assign every member of one group to drink plenty of milk daily for several decades, while the other group would drink some kind of milk placebo instead. Obviously, this is too difficult to do in practice.

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What we can do instead is to take many thousands of people, ask them how much milk they’ve been drinking over the years, and then follow them for at least a decade to see whether the people who regularly drink milk are any less likely to suffer from broken bones later in life.

This is what happened in research published in 1997 conducted by Harvard University. An impressive 77,000 female nurses were followed for 10 years. The researchers found no significant difference in the numbers of arm or hip fractures between those who drank one glass of milk a week or less and those who drank two or more.