There isn’t a single number in grams or pounds that defines “normal” bone mass for your age. Instead, bone health is measured through a bone mineral density (BMD) test, and your result is reported as a score that compares you to either a healthy young adult or to people your own age. Understanding which score applies to you, and what the numbers mean, is the key to knowing where you stand.
How Bone Density Is Actually Measured
A bone density test uses a type of low-dose X-ray called a DEXA scan. It measures the mineral content in specific bones, usually the hip and spine. The result isn’t given as a weight or mass in grams. Instead, you receive one of two scores depending on your age and sex: a T-score or a Z-score.
If you’re a postmenopausal woman or a man aged 50 or older, your result will be a T-score. This compares your bone density to that of a healthy 30-year-old of the same sex, which represents peak bone mass. The World Health Organization defines three categories:
- Normal: T-score of -1.0 or above
- Low bone mass (osteopenia): T-score between -1.0 and -2.5
- Osteoporosis: T-score of -2.5 or below
If you’re a premenopausal woman, a man under 50, or a child, your result will be a Z-score. This compares your density to the average for healthy people of the same age, sex, and ethnicity. A Z-score of -2.0 or lower means your bone density is significantly below what’s expected for someone your age, and it may point to bone loss caused by a medication, hormonal condition, or other underlying issue.
When Your Bones Are at Their Strongest
Your skeleton isn’t static. Bone is living tissue that’s constantly being broken down and rebuilt. During childhood and adolescence, new bone forms faster than old bone is removed, so your total bone mass climbs steadily. It eventually plateaus at what’s called peak bone mass.
Women typically reach peak bone mineral density around age 22. Men reach it later, closer to age 27. These ages matter because the higher your peak, the larger the “bank account” of bone you carry into middle and older age. Genetics accounts for roughly 60 to 80 percent of peak bone mass, but physical activity, nutrition, and hormonal health during your teens and twenties shape the rest. If you’re in that age range now, you’re still in a window where building bone is possible in a meaningful way.
How Bone Loss Progresses With Age
After peak bone mass, everyone loses bone gradually. For both men and women, the process is slow at first. But the timeline and pace differ significantly by sex.
For women, the sharpest drop begins at menopause. Estrogen plays a major role in maintaining bone, and as estrogen levels fall, bone breakdown accelerates. On average, women lose about 1.9 percent of their bone mineral density per year from menopause through their late sixties. That may sound small, but it compounds. Over the first decade after menopause, a woman can lose 10 to 20 percent of her total bone density if nothing is done to slow the process.
Men lose bone more gradually. They don’t experience the same hormonal cliff, so the decline is steadier and starts later. Still, men over 65 do experience meaningful bone loss at the hip and spine, and fracture risk rises with age. Osteoporosis in men is underdiagnosed partly because it’s so strongly associated with women, but the condition is far from rare in older men.
Ethnicity and Body Type Affect Your Baseline
Bone density varies across ethnic groups, which is one reason the Z-score adjusts for ethnicity. Black men, for example, have femoral neck bone density that’s about 13 percent higher than white men and about 6 percent higher than Hispanic men. These differences hold across age groups, though the rate of age-related decline can vary too. Hispanic men, for instance, tend to lose hip bone density at a steeper rate than Black or white men as they age.
Body weight also plays a role. Heavier individuals tend to have higher bone density because their skeleton adapts to carrying more load. Conversely, people with very low body weight or a history of eating disorders often have significantly lower bone mass than expected for their age.
What You Can Do to Protect Bone Mass
The most effective strategy depends on where you are in life. Before your mid-twenties, the goal is building the highest peak bone mass possible. After that, the goal shifts to slowing loss and, in some cases, modestly reversing it.
Weight-Bearing and Resistance Exercise
Exercise is one of the few interventions shown to actually increase bone density in adults who’ve already passed peak bone mass. In clinical trials, men with low bone mass who did resistance training or jumping exercises for 12 months increased whole-body bone density by 0.6 percent and spine density by 1.3 percent. Other studies have shown increases of 1.5 to 3.8 percent at the hip and spine with progressive resistance training in men aged 50 to 80. These gains are modest in absolute terms, but they effectively reverse the annual bone loss that comes with normal aging. Walking, running, dancing, and stair climbing all count as weight-bearing exercise. Swimming and cycling, while excellent for cardiovascular health, don’t load the skeleton enough to stimulate bone growth.
Calcium and Vitamin D
Adults aged 19 to 50 need about 1,000 milligrams of calcium and 600 IU of vitamin D daily. Calcium needs rise to 1,200 milligrams for women over 50 and men over 70. Vitamin D is essential because without it, your body can’t absorb calcium efficiently. Dairy products, leafy greens, fortified foods, and canned fish with bones are all practical sources. If your diet falls short, a supplement can fill the gap, but more isn’t necessarily better. Excess calcium from supplements (above 2,000 to 2,500 milligrams daily) has been linked to kidney stones and possibly cardiovascular issues.
Understanding Your Fracture Risk
Bone density alone doesn’t tell the whole story. A tool called FRAX, developed by the World Health Organization, estimates your 10-year probability of a major fracture by combining your bone density score with other risk factors: your age, sex, BMI, whether you’ve had a previous fracture, whether a parent broke a hip, smoking status, alcohol intake, use of glucocorticoid medications (like prednisone), and whether you have rheumatoid arthritis or other conditions that weaken bone. Your doctor can run this calculator using your DEXA results, and it gives a more complete picture than a T-score alone.
This is especially useful for people with osteopenia, the gray zone between normal and osteoporosis. A T-score of -1.5 in a 55-year-old with no other risk factors carries a very different fracture probability than the same score in a 75-year-old who smokes, takes steroids, and has already broken a wrist.
When to Get Tested
Routine DEXA screening is recommended for all women aged 65 and older and men aged 70 and older. Earlier testing makes sense if you have risk factors: early menopause, long-term steroid use, a family history of osteoporosis, low body weight, a history of fractures from minor falls, or conditions like celiac disease or hyperthyroidism that interfere with bone metabolism. If your initial scan shows normal density, repeat testing every few years is usually sufficient. If it shows osteopenia or osteoporosis, your doctor will likely recommend more frequent monitoring to track whether treatment is working.