How osteoporosis develops in your bones

Osteoporosis happens when your bones lose density faster than your body can replace it. Your skeleton is living tissue that constantly breaks down old bone and builds new bone. Until around age 30, new bone is added faster than old bone is removed, so bone mass increases. After that, bone remodeling continues, but you lose slightly more bone mass than you gain.

Whether you develop osteoporosis depends on how much bone mass you reach by age 30 (called peak bone mass) and how quickly you lose it afterward. The higher your peak bone mass, the more bone you can afford to lose later and still have strong bones. Low peak bone mass is one reason some people develop osteoporosis; rapid bone loss after that is another.

Key Takeaways

  • Osteoporosis develops when bone loss outpaces bone formation, a process that accelerates after menopause in women and gradually in men starting around age 70.
  • Estrogen and testosterone slow bone loss, so menopause, low hormone levels, and hormone-blocking cancer treatments all increase your risk.
  • Not enough calcium and vitamin D, lack of weight-bearing exercise, and certain medications like corticosteroids speed up bone loss.
  • Some people inherit genes that affect how much bone they build or how fast they lose it, making family history an important risk factor.
  • Conditions like rheumatoid arthritis, celiac disease, and kidney disease interfere with bone health through inflammation or nutrient absorption.

Hormones and bone loss across your lifetime

Hormones are the biggest driver of when and how fast you lose bone. In women, estrogen protects bone density. When estrogen drops sharply during menopause, bone loss accelerates — women can lose up to 10 percent of bone mass in the five years after their last period. This is why osteoporosis is far more common in women over 50 than in men the same age.

Men lose bone more slowly because testosterone declines gradually over decades rather than dropping suddenly. Men typically don't face rapid bone loss until around age 70, when testosterone levels fall enough to affect bone density. Men who have low testosterone from any cause — including some cancer treatments — face higher risk at younger ages.

Other hormone changes also matter. Thyroid hormone, parathyroid hormone, and cortisol all influence how fast bone breaks down. Overactive thyroid, untreated parathyroid disease, and chronic stress (which raises cortisol) can all speed bone loss.

Calcium, vitamin D, and nutrition

Your body needs calcium to build and maintain bone. If you don't take in enough calcium, your body pulls it from your bones to keep your blood calcium stable. Over time, this weakens your skeleton. Most adults need 1,000 to 1,200 mg of calcium daily, depending on age and sex.

Vitamin D is equally important because it helps your intestines absorb calcium. Without enough vitamin D, you absorb less calcium even if you eat plenty of it. Your skin makes vitamin D when exposed to sunlight, but many people — especially those who live far north, spend little time outdoors, or have darker skin — don't make enough. Vitamin D also comes from fatty fish, egg yolks, and fortified milk, but most people need a supplement to reach the recommended 600 to 800 IU daily.

Protein matters too. Bone is partly made of protein, and people who eat too little protein lose bone faster. Excessive salt, caffeine, and alcohol can also increase calcium loss through urine, though the effect is usually small unless intake is very high.

Physical activity and bone strength

Bones respond to weight and stress by building strength. Weight-bearing exercise — walking, jogging, dancing, climbing stairs, or lifting weights — signals your bones to maintain or build density. People who are sedentary lose bone faster because their bones receive no signal to stay strong.

Bed rest, immobility from injury, and jobs or lifestyles that keep you sitting most of the day all contribute to bone loss. Astronauts in zero gravity lose bone at a dramatic rate because gravity provides no stimulus. On Earth, even a few weeks of reduced activity can slow bone formation.

The type of exercise matters. Weight-bearing and muscle-strengthening activities are most protective. Swimming and cycling, while excellent for overall health, don't stress bone the way walking or resistance training do, so they're less effective at preventing bone loss.

Medications and medical conditions that weaken bone

Corticosteroids like prednisone are among the strongest bone-weakening drugs. Even low doses taken for months can increase bone loss. Other medications that affect bone include some seizure drugs, certain cancer treatments (especially aromatase inhibitors for breast cancer and androgen deprivation therapy for prostate cancer), and long-term use of some stomach acid reducers.

Several medical conditions increase bone loss. Rheumatoid arthritis causes inflammation that speeds bone breakdown. Celiac disease and inflammatory bowel disease damage the intestines, reducing calcium and vitamin D absorption. Chronic kidney disease disrupts vitamin D set up and phosphate balance. Type 1 diabetes is linked to lower bone density despite normal or high bone mass. Hyperthyroidism, whether from Graves' disease or too much thyroid medication, increases bone turnover.

Cancer, especially multiple myeloma, can directly destroy bone. Eating disorders cause severe malnutrition and hormone disruption. Chronic liver disease interferes with vitamin D set up.

Genetics and family history

Your genes influence how much bone mass you build by age 30 and how fast you lose it later. If your parents or siblings have osteoporosis, your risk is higher. This doesn't mean you will develop it, but it means you start with either lower peak bone mass or a faster bone-loss rate — or both.

Certain ethnic groups have different average bone density. People of African descent typically have higher bone density and lower fracture risk. People of European and Asian descent tend to have lower bone density. These are population averages; individual variation is large.

Age, sex, and other unchangeable risk factors

Age is a major risk factor. The older you are, the more bone you've lost and the higher your fracture risk. Women over 50 and men over 70 face the steepest risk.

Being female is itself a risk factor, partly because women have smaller bones on average and partly because of the sharp estrogen drop at menopause. A woman's lifetime fracture risk from osteoporosis is about one in three; a man's is about one in five.

Small body frame increases risk. If you weigh less, you have less bone mass to draw from as you age. People with a body mass index below 19 face higher fracture risk.

Frequently Asked Questions

Can you get osteoporosis if you're young?

Yes. Young adults can develop osteoporosis from prolonged immobility, eating disorders, certain medications like corticosteroids, hormonal conditions, or genetic factors. It's less common than in older adults, but it happens. Bone density screening can identify it.

Does osteoporosis run in families?

Bone density and bone-loss rate are partly inherited, so family history matters. If a parent had osteoporosis or a fracture from a fall, your risk is higher. This is one reason doctors ask about family history when assessing bone health.

Can you reverse osteoporosis?

You cannot fully reverse bone loss, but you can slow it and sometimes stabilize it. Adequate calcium and vitamin D, weight-bearing exercise, and medications can stop further loss and reduce fracture risk. Early detection and treatment work better than waiting until fractures occur.

Does caffeine cause osteoporosis?

Caffeine increases calcium loss in urine slightly, but the effect is small — about 2 to 3 mg per cup of coffee. As long as you get enough calcium overall, moderate caffeine use doesn't cause osteoporosis. Very high intake (more than 400 mg daily) combined with low calcium intake is more concerning.

What's the difference between osteoporosis and osteopenia?

Osteopenia means your bone density is lower than normal but not low enough to be called osteoporosis. It's an earlier stage. Not everyone with osteopenia develops osteoporosis, but it signals that bone loss is happening faster than it should, and lifestyle changes or treatment may help prevent progression.