Osteoporosis happens when your body loses bone faster than it can rebuild it, leaving bones porous, brittle, and vulnerable to fractures. About 12.6% of adults over 50 in the United States have osteoporosis, and the condition is nearly four times more common in women (19.6%) than in men (4.4%). While most people associate it with aging, the causes run deeper, spanning hormones, genetics, nutrition, lifestyle, medications, and other medical conditions.
How Bone Breaks Down Faster Than It Rebuilds
Bone is living tissue that constantly renews itself through a process called remodeling. Specialized cells called osteoclasts dissolve old or damaged bone, while another set of cells called osteoblasts fill in the gaps with new bone. In healthy adults, this cycle stays roughly balanced. In osteoporosis, the balance tips: bone is removed faster than it’s replaced, and the internal structure becomes increasingly hollow and fragile.
This imbalance often starts at the cellular level. When osteoclasts carve out bone, they also trigger nearby stem cells to multiply and eventually become new bone-building cells. But that process depends on reaching a critical threshold of new cells at the resorption site. If too few bone-building cells arrive, or they arrive too slowly, the gap left behind never fully fills in. Over time, each remodeling cycle leaves the bone a little weaker than before.
The Role of Estrogen and Menopause
Estrogen is the single most important hormone for maintaining bone density in women. It slows the rate at which osteoclasts break down bone, essentially acting as a brake on resorption. When estrogen levels drop sharply during menopause, that brake releases, and bone loss accelerates dramatically. A woman can lose up to 20% of her bone density in the five to seven years following menopause.
This is the primary reason osteoporosis hits women so much harder than men. Among women 65 and older, 27.1% have osteoporosis, compared with 5.7% of men the same age. Men do lose bone as testosterone gradually declines with age, but the drop is slower and less severe than the estrogen cliff that accompanies menopause.
Women who experience early menopause (before age 45), whether naturally or after surgical removal of the ovaries, face an even longer window of accelerated bone loss and correspondingly higher risk.
Peak Bone Mass Sets the Starting Line
Your skeleton isn’t static. It grows denser throughout childhood and adolescence, reaching its maximum strength, called peak bone mass, between the ages of 25 and 30. About 95% of a young woman’s peak bone mass is already in place by age 20. For boys, the fastest bone growth happens between ages 13 and 14, with peak mass arriving roughly 9 to 12 months after their biggest growth spurt in height.
Think of peak bone mass as a savings account. The more bone you deposit during your teens and twenties, the larger your reserve when age-related losses begin. People who never build a strong peak, whether due to poor nutrition, chronic illness during childhood, or a sedentary adolescence, enter midlife with less bone to spare. That means even normal rates of bone loss can push them into osteoporosis territory earlier.
Nutritional Deficiencies That Weaken Bone
Calcium and vitamin D are the two nutrients most directly tied to bone health, and falling short on either one contributes to osteoporosis. Calcium is the primary mineral embedded in bone tissue. Vitamin D controls how efficiently your intestines absorb calcium from food. Without enough vitamin D, you can eat plenty of calcium-rich foods and still not get much of it into your bones.
Adults over 51 need 1,000 to 1,200 mg of calcium per day, roughly the equivalent of three to four servings of dairy or calcium-fortified foods. The recommended vitamin D intake for most adults is 600 international units daily, though many experts argue this is too conservative for older adults. Chronic deficiency in either nutrient forces the body to pull calcium from the skeleton to maintain blood calcium levels, quietly thinning bone over years.
Protein also matters more than most people realize. Bone is about 50% protein by volume, and diets very low in protein are associated with reduced bone density. Excessive alcohol (more than two drinks a day) and heavy caffeine intake can also interfere with calcium absorption.
Medications That Cause Bone Loss
Glucocorticoids, the class of steroids prescribed for conditions like asthma, rheumatoid arthritis, and inflammatory bowel disease, are the most common medication-related cause of osteoporosis. According to the American College of Rheumatology, people taking more than 2.5 mg per day for three months or longer face significantly higher fracture risk. These drugs suppress bone formation while simultaneously increasing bone breakdown, a double hit that can cause rapid loss.
Other medications linked to bone loss include certain seizure drugs, proton pump inhibitors used for acid reflux, some cancer treatments (particularly those that lower sex hormones), and high-dose thyroid hormone replacement. If you take any of these long-term, bone density monitoring becomes especially important.
Medical Conditions That Contribute
A number of diseases accelerate bone loss through different pathways. Celiac disease damages the lining of the small intestine, reducing absorption of calcium and vitamin D. The bone damage from celiac disease is driven by two forces: this malabsorption and the chronic inflammation the disease creates, both of which independently weaken bone.
Hyperthyroidism speeds up the entire remodeling cycle, but bone removal outpaces bone rebuilding, leading to net loss. Rheumatoid arthritis contributes through both inflammation and the glucocorticoid medications often used to treat it. Type 1 diabetes, hyperparathyroidism, and chronic kidney disease all carry elevated osteoporosis risk as well. In many cases, treating the underlying condition can slow or partially reverse the bone loss it causes.
Lifestyle and Genetic Factors
Physical activity is one of the strongest modifiable factors in bone health. Weight-bearing exercise, anything that forces you to work against gravity like walking, running, or lifting weights, stimulates bone-building cells to lay down new tissue. A sedentary lifestyle removes this stimulus, and prolonged bed rest or immobility can cause bone loss surprisingly fast, on the order of 1% to 2% per month in some cases.
Smoking is independently toxic to bone. It reduces blood supply to the skeleton, interferes with calcium absorption, and appears to directly impair the function of bone-building cells. Current smokers consistently show lower bone density than nonsmokers, and the effect is dose-dependent: the more you smoke and the longer you’ve smoked, the worse it gets.
Genetics also play a substantial role. If a parent fractured a hip, your own fracture risk is elevated. Body frame size matters too. People with naturally smaller, thinner frames start with less bone mass, giving them a smaller margin before bone loss becomes clinically significant. Ethnicity influences risk as well: white and Asian women have the highest rates of osteoporosis, though the condition affects all racial and ethnic groups.
How Osteoporosis Is Identified
Osteoporosis is diagnosed with a bone density scan, a painless imaging test that typically measures the hip and spine. The result is reported as a T-score, which compares your bone density to that of a healthy 30-year-old. A T-score of negative 1 or higher is normal. Between negative 1 and negative 2.5 indicates osteopenia, a milder form of bone loss that signals elevated risk. A T-score of negative 2.5 or lower means osteoporosis.
The tricky part is that osteoporosis causes no symptoms until a fracture occurs. Many people discover they have it only after breaking a bone from a minor fall or even a sudden twist. Compression fractures in the spine can happen without any obvious injury, gradually causing height loss and a rounded upper back. This is why screening is recommended for all women at age 65 and for younger postmenopausal women with risk factors.