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A femur looks like a solid thing on an X-ray, but it is closer to a scaffold under permanent renovation. Your skeleton tears down old bone and lays down new bone all day, every day, and until roughly your late twenties the builders outpace the demolition crew. After that the balance tips. Osteoporosis is what happens when it tips far enough that a stumble on the kerb, or a hard cough, can crack a vertebra.
The numbers are not small. Roughly one in three women and one in five men over 50 will break a bone because of osteoporosis. A hip fracture in your eighties carries a mortality rate comparable to some cancers in the year that follows.
Some of that risk is baked in: your age, your genes, your hormones. A surprising amount is not. Here are the seven factors clinicians weigh most heavily, roughly in order of how much they shift the odds.
1. Age, oestrogen loss, and being female
Bone mineral density peaks somewhere around age 30, then slides by roughly 0.5 to 1 percent a year in both sexes. For women, menopause compresses a decade of that slide into a handful of years. Oestrogen is a brake on bone breakdown, and when it falls, the brake comes off. Women can lose between 10 and 20 percent of their bone density in the five to seven years after their last period.
Men follow the same curve, just later and flatter, with the decline steepening after about 65, particularly when testosterone is low. Early menopause, whether surgical or spontaneous, before age 45 moves a woman onto the faster track years ahead of schedule.
2. A fracture you’ve already had
This is the strongest single predictor in the whole list. If you broke a wrist catching yourself at 55, or cracked a rib doing something unremarkable, that is a red flag rather than bad luck. A previous fragility fracture roughly doubles your risk of another one, and the next one is often in the spine or hip.
Watch for the quieter signs too: a loss of more than 4 cm in height, a stoop that wasn’t there five years ago, or a band of chronic back pain that came on without a clear injury. Vertebral fractures are routinely missed because they’re dismissed as a pulled muscle.
3. Low body weight and a small frame
Thin people break more bones. Part of it is mechanical: less body weight means less load on the skeleton, and bone responds to load. Part of it is hormonal, since fat tissue converts androgens into a small but meaningful supply of oestrogen. A BMI under 19, or a weight below about 57 kg (127 lb), is one of the items on the standard osteoporosis risk checklist.
Low muscle mass matters for a second reason. Weak legs and poor balance make falls more likely, and a fall is the event that turns brittle bone into a hospital admission.
4. Smoking and heavy drinking
Smoking is bad for bone in at least three ways. Nicotine and cadmium are directly toxic to osteoblasts, the cells that build bone. Smoking lowers circulating oestrogen and speeds up the breakdown of any HRT you take. It also tends to push people towards lower body weight and poorer diets. Smokers run somewhere in the region of 30 to 40 percent higher hip fracture risk than non-smokers.
It’s the same habit driving a lot of lung disease, which is why the risk factors for COPD overlap so heavily with these. On the alcohol side, more than two drinks a day on a regular basis interferes with vitamin D metabolism, suppresses bone formation and increases the odds of a fall.
5. Long-term steroid use and a long list of other drugs
Glucocorticoids are the big one. Prednisone at 5 mg or more daily for three months or longer causes the fastest drug-induced bone loss we know of, with the steepest drop in the first six to twelve months of treatment. Asthma, rheumatoid arthritis, inflammatory bowel disease and polymyalgia all regularly put people on that dose for years.
Other medications that show up on the list include:
- Proton pump inhibitors (omeprazole and relatives) taken for more than a year
- SSRIs, which are linked to lower bone density and more falls
- Aromatase inhibitors and androgen deprivation therapy in cancer treatment
- Certain diabetes drugs such as pioglitazone and rosiglitazone
- Depot medroxyprogesterone (the injection) used long-term for contraception
Even the treatments have trade-offs. Bisphosphonates and other antiresorptives reduce fracture risk substantially, but long-term use is associated with rare complications, including jaw disease after dental work, which is one reason dentists ask about your bone medication history before an extraction.
There is also a live research thread on serotonin. Gut-derived serotonin appears to suppress bone formation, and the neurotransmitter is being studied as both a marker and a driver of bone loss, which complicates the assumption that SSRIs are neutral for the skeleton.
6. A diet that starves the bone of raw material
Bone is roughly 40 percent mineral and 50 percent protein by volume, and most people under-supply at least one of those. Calcium intake in British and North American adults averages well below the recommended 1,000 to 1,200 mg a day, and low vitamin D is common enough in northern latitudes that supplementation is routine.
Practical daily targets for most adults over 50:
- Calcium: 1,000 mg (men 50–70) or 1,200 mg (women 51+, men 71+). That’s about three servings of dairy, or fortified plant milk plus tofu and leafy greens.
- Vitamin D: 800–1,000 IU from October to March if you live above roughly Birmingham or Seattle.
- Protein: 1.0–1.2 g per kg of body weight, spread across meals. A 70 kg adult needs around 75–85 g.
- Fruit and vegetables: five portions, for potassium, magnesium and vitamin K.
Nutrition advice in this area gets noisy fast, and some of the most contested nutrition claims concern dairy, salt and acid-load diets. The boring consensus holds up: enough calcium, enough protein, enough vitamin D, not too much salt or caffeine.
7. Sitting still
Bone is lazy in the sense that it only invests in strength where it detects strain. Astronauts lose 1 to 1.5 percent of bone density per month in orbit despite exercising, because the loading is gone. Bed rest does something similar in a fraction of the time.
What the skeleton responds to is impact and resistance: brisk walking, stair climbing, gardening with actual digging, resistance bands, loaded carries, dancing. Three or four sessions a week of something that makes your muscles work against gravity is the target. Swimming and cycling are excellent for your heart and useless for your hip density. Balance work matters just as much, because a strong bone that hits the floor is still a fracture.
Who should ask for a scan
A DEXA scan takes about ten minutes, uses a fraction of a chest X-ray’s radiation, and gives a T-score. Anything at or below -2.5 is osteoporosis; between -1 and -2.5 is osteopenia, the grey zone where lifestyle changes still buy you time.
Guidelines generally suggest scanning women at 65 and men at 70, and earlier if you have any of the factors above, particularly a previous fracture, long-term steroid use, early menopause, a BMI under 19, or a parent who broke a hip. Height loss, a new stoop, or a fracture from a fall at standing height are reasons to ask sooner rather than wait for the invite.
Bone loss is silent until it isn’t. There is no ache, no visible warning, and the first symptom is often the fracture itself. But the variables that decide how fast you lose bone are, for the most part, things you can measure, discuss and change. A conversation with a GP about a scan and a realistic look at your diet, your smoking and your walking route up the stairs will do more for your skeleton in the next decade than any supplement on the shelf.
