Why do bones become fragile with age?
Bone renews itself constantly: some cells dig into it, others fill it back in. Until about age 30, more is filled in than dug out. After that, each hole is filled a little less well, and in women the loss speeds up around the last period.
Drag the age: the animation shows a corner of bone under the microscope, and the curve shows bone mass over a lifetime.
Simplified curves, as a percentage of each person's maximum. For women, the last period is placed at age 51.
How does bone renew itself?
In small work sites. An osteoclast dissolves a little bone over a few weeks, then osteoblasts lay down new bone over a few months. An adult skeleton renews itself this way by around 10% a year, a common estimate. This constant work repairs micro-cracks and releases calcium when the blood needs it.
When is bone mass at its highest?
It is built mainly during childhood and adolescence, and peaks in early adulthood (Weaver, 2016). The higher this capital, the more you have in reserve when loss begins.
What happens at menopause?
The drop in estradiol frees the osteoclasts. In a large American study, loss begins a year before the last period. Over 10 years, the vertebrae lose 10.6% of their density, including 7.4% between one year before and two years after the last period; the femoral neck loses 9.1% (Greendale, 2012).
| Period | Vertebrae | Femoral neck |
|---|---|---|
| From 1 year before to 2 years after the last period | 7,4 % | 5,8 % |
| Total over 10 years (5 years before, 5 years after) | 10,6 % | 9,1 % |
Source: SWAN study, 862 women followed (Greendale, 2012).
What helps bones?
Bones get stronger where they are loaded: impact sports (running, jumping) and strength training stimulate them, especially during growth. Calcium and vitamin D provide the material; smoking and excess alcohol make you lose it (Weaver, 2016; Compston, 2019).
Frequently asked questions
Does osteoporosis hurt?
No, not as long as there is no fracture. That is why it is often discovered after a fall, at the wrist, hip or vertebrae (Compston, 2019).
What does the osteoclast do, besides destroying bone?
It removes old or cracked bone so it can be replaced: without it, bone becomes dense but brittle (this is osteopetrosis). As it digs, it releases growth factors stored in the bone (TGF-β, IGF-1) and sends its own signals, which call in the osteoblasts: it is the one that starts the rebuilding work. It also releases calcium into the blood when the body needs it.
How is bone strength measured?
With a bone density scan, a very low-dose X-ray that measures the density of the hip and vertebrae. The result is compared with that of a young adult (the T-score).
Are men affected?
Yes, but later and less often: they start from a higher capital and do not go through a sudden hormone drop like menopause.
Is it too late to act after 50?
No. Physical activity, calcium, vitamin D and fall prevention remain useful, and medicines exist. Talk to your doctor.
See also
Vitamin D and sunlight Menopause Gelatin and tendons
Sources
- Compston JE, McClung MR, Leslie WD. Osteoporosis. Lancet. 2019;393(10169):364-76. PMID 30696576
- Weaver CM, et al. The National Osteoporosis Foundation's position statement on peak bone mass development and lifestyle factors. Osteoporos Int. 2016;27(4):1281-386. PMID 26856587
- Greendale GA, et al. Bone mineral density loss in relation to the final menstrual period in a multiethnic cohort (SWAN). J Bone Miner Res. 2012;27(1):111-8. PMID 21976317
- Charles JF, Aliprantis AO. Osteoclasts: more than 'bone eaters'. Trends Mol Med. 2014;20(8):449-59. PMC4119859
- Daponte V, et al. Current perspectives on the multiple roles of osteoclasts: mechanisms of osteoclast-osteoblast communication and potential clinical implications. eLife. 2024;13:RP95083. doi:10.7554/eLife.95083