On her 86th birthday in December, Jane Fonda declared herself the happiest she’d ever been. The actor reportedly put her younger cast mates to shame on the set of her recent movie, Book Club: The Next Chapter; rising at dawn and clocking up thousands of steps around the streets of Rome before her day began.

Fonda and many of her fellow seniors – including the baby boomer bubble now in their mid-70s – are living longer and healthier lives than any generation before them. That longevity seems set to continue for the following generations; people in their 50s and 60s can now reasonably expect to see their 90s. Older people are more active and generally healthier than ever before.

But while we’re out there biking the trails and walking the tracks, there can be changes going on inside the body that might put paid to that extended health span. Diseases of the bones and brain can stealthily start decades ahead of when they finally show up externally. Scientists are learning more, not only about new ways to treat these issues, but also about what individuals can do to lower their risk and potentially prevent them.

The fact that we’re living longer is one reason bone health is becoming more of a focus for innovative research. Unless we’ve broken bones, it’s likely we’ve devoted little time to thinking about their health. Yet bone density is linked to longevity – and having poor bone density is linked to early death.

Early in Ian Reid’s career as an endocrinologist, he started to realise that bones needed more attention.

“The epidemic of heart disease was beginning to get under control,” says Reid, a distinguished professor at the University of Auckland. “One of the problems cardiologists caused for us by not letting us die of a heart attack at three score years and 10 was that we lived to four score years and more,