How to Prevent Osteoporosis

Four things, in order of how much they matter. Load your skeleton regularly with weight-bearing and resistance exercise. Get enough calcium, ideally from food. Take a daily vitamin D supplement, which at Ireland's latitude is necessary for most people for most of the year. And remove what strips bone away — smoking, heavy alcohol, being underweight, and untreated conditions such as coeliac disease. None of these works in isolation.

Not guaranteed, because age, sex, genetics and menopause are not negotiable. What you can change is how much bone you build before 30 and how fast you lose it afterwards, and that difference is large enough to determine whether you ever reach the fracture threshold. Prevention shifts the odds substantially; it does not remove the risk entirely.

Adolescence, when about half of adult bone mass is laid down, is the highest-leverage window. In practice most people start thinking about it in their forties or fifties, and that is still worthwhile. The years either side of menopause matter especially for women, because that is when the steepest loss of their life happens.

No. Calcium and vitamin D are necessary but not sufficient, because bone rebuilds in response to mechanical loading. A perfect diet with no weight-bearing activity will not maintain bone density. Diet supplies the raw material; exercise provides the instruction to use it.