The causes of osteoporosis all lead to the same imbalance: the body breaks down old bone faster than it builds new bone, so the skeleton slowly loses mass and strength. In most people, this imbalance comes from aging combined with the drop in sex hormones, especially estrogen after menopause. This is called primary osteoporosis. In others, a medical condition or medication speeds up bone loss. This is secondary osteoporosis. It is often missed and is sometimes reversible.
Osteoporosis causes no symptoms until a bone breaks. That is why knowing the causes matters. It tells you who should be screened, and it tells your doctor what to look for before assuming bone loss is “just age.”
How Healthy Bone Is Built and Broken Down
Bone is living tissue that is constantly renewed through remodeling. Cells called osteoclasts dissolve small areas of old bone. Cells called osteoblasts then fill the gap with new bone, which becomes mineralized with calcium and phosphate. In healthy adults the two processes are balanced, and the skeleton is gradually replaced over years.
The balance is controlled by hormones and local signals. RANKL switches osteoclasts on, and its natural decoy, osteoprotegerin (OPG), switches them off. Estrogen, testosterone, parathyroid hormone, vitamin D and physical loading all shift the balance. Anything that increases osteoclast activity or reduces osteoblast activity leads to net bone loss.
Peak Bone Mass: The Foundation You Build Early
Most people reach their peak bone mass by around age 30. After that, bone density slowly declines. How much bone you build in childhood and early adulthood decides how much you can lose later before fractures become likely.
Genetics account for much of the difference in peak bone mass between people. Childhood nutrition, calcium and vitamin D intake, physical activity, and the timing of puberty also play a part. Late puberty, eating disorders and long periods without menstruation in young women can all reduce the bone “savings” carried into later life.
Primary Causes: Aging and Hormones
Menopause and estrogen loss
Estrogen restrains osteoclasts. When estrogen falls at menopause, osteoclasts become more numerous and live longer, and bone is resorbed faster than it can be replaced. Bone loss is fastest in the first several years after menopause. This is the main reason women develop osteoporosis more often and earlier than men.
Aging in both sexes
With age, osteoblasts become less effective, calcium absorption from the gut falls, and the skin makes less vitamin D. Men lose bone more gradually. Falling testosterone, which the body partly converts into estrogen, contributes to their loss. Older age also increases the risk of falls, which turns weak bone into fractures.
Secondary Causes: Diseases and Medications
A secondary cause should be considered in men, in premenopausal women, and in anyone whose bone density is much lower than expected for their age. Common examples are listed below.
| Category | Examples | How it harms bone |
|---|---|---|
| Medications | Long-term glucocorticoids (such as prednisone), excess thyroid hormone, aromatase inhibitors, androgen-deprivation therapy, some anticonvulsants, long-term heparin | Suppress bone formation or speed resorption |
| Endocrine disorders | Hyperparathyroidism, hyperthyroidism, Cushing’s syndrome, hypogonadism, diabetes | Hormone excess or deficiency upsets remodeling |
| Gut and nutrition | Celiac disease, inflammatory bowel disease, bariatric surgery, low calcium or vitamin D | Poor absorption of calcium and vitamin D |
| Inflammatory disease | Rheumatoid arthritis, other chronic inflammatory conditions | Inflammatory signals activate osteoclasts |
| Blood and marrow disorders | Multiple myeloma, systemic mastocytosis, thalassemia | Marrow cells release factors that dissolve bone |
| Kidney and liver disease | Chronic kidney disease, chronic liver disease | Disturbed mineral and vitamin D metabolism |
Glucocorticoids are the most common drug cause. Bone loss begins within months of starting them. Anyone taking the equivalent of 5 mg of prednisone daily for three months or longer should have their bone health assessed.
As a hematologist, I pay particular attention to multiple myeloma. It can cause unexplained low bone density or spinal fractures, especially in older adults, and is diagnosed with simple blood and urine protein tests.
Lifestyle Factors You Can Change
- Inactivity: bone responds to load. Long periods of bed rest or a sedentary lifestyle speed up loss.
- Smoking: lowers estrogen levels and impairs osteoblast function.
- Excess alcohol: harms bone-forming cells and increases falls.
- Low body weight: less mechanical loading and, in women, often lower estrogen.
- Diet low in calcium, vitamin D or protein: leaves too little raw material for new bone.
The factors you cannot change include age, female sex, a parent with a hip fracture, and your own previous fragility fracture. These are combined with bone density in fracture-risk calculators such as FRAX.
How the Cause Is Identified
Diagnosis uses a DEXA scan to measure bone mineral density. The result is reported as a T-score, which compares you with a healthy young adult.
| T-score | Interpretation |
|---|---|
| -1.0 or higher | Normal bone density |
| Between -1.0 and -2.5 | Low bone mass (osteopenia) |
| -2.5 or lower | Osteoporosis |
Once osteoporosis is confirmed, basic blood tests look for secondary causes. These typically include calcium, kidney and liver function, vitamin D, parathyroid hormone and thyroid function, and sometimes testosterone, celiac antibodies or serum protein electrophoresis. Finding and treating a secondary cause can stop further bone loss. Treatment for established disease is covered in our article on osteoporosis treatment and in our broader osteoporosis guide.
When to See a Doctor
Ask about a bone density test if you are a woman aged 65 or older, a postmenopausal woman with risk factors, or a man with risk factors. Also ask if you have had a fracture from a minor fall, or if you have lost noticeable height or developed a stooped posture. Anyone starting long-term steroid treatment should discuss bone protection at the same time.
Frequently Asked Questions
Can men get osteoporosis?
Yes. Men start with larger, denser bones and lose bone more slowly, but osteoporosis in men is common in later life. Men are more likely than women to have a secondary cause such as low testosterone, steroid use or excess alcohol.
Is osteoporosis hereditary?
Genes strongly influence peak bone mass. A parent’s history of hip fracture is a recognized risk factor. Inheriting risk does not make osteoporosis inevitable, since exercise, nutrition and early treatment still make a real difference.
Can osteoporosis be caused by medication?
Yes. Long-term glucocorticoids are the most common cause of drug-induced osteoporosis. Some breast and prostate cancer hormone treatments, excess thyroid hormone replacement and some anticonvulsants can also thin bone. Never stop a prescribed drug on your own. Instead, ask your doctor about bone monitoring and protection.
Can bone loss be reversed?
Treatment can stop bone loss and partly rebuild density, especially bone-forming drugs and correcting a secondary cause. The main goal is to reduce fracture risk rather than restore youthful bone.
