What Is the Average Bone Mass and How Is It Measured?

The mineral in an adult skeleton weighs far less than most people guess: typically 1.5 to 2.5 kg (3.3 to 5.5 lb) in women and 2.5 to 3.5 kg (5.5 to 7.7 lb) in men. It is measured with a quick, low-dose x-ray scan that can tell bone apart from fat and muscle.1Scintica. Dual Energy X-Ray Absorptiometry How Does it Work? That total says little about fracture risk, though. What matters most to doctors is how dense your hip and spine are compared with a healthy young adult.

Typical Bone Mass for Women and Men

A scan report shows only the mineral, which is why its number is so much lighter than the skeleton weight. Living bone also holds water, collagen and marrow, which the scan doesn’t count as mineral.

Gyms and clinics that offer body scans often list bone mineral alongside fat and lean mass. A result within the typical range for your sex doesn’t rule out thin bone, since these scans don’t measure density at the hip and spine.

The ranges are wide because frame size varies a lot between healthy adults. Bone mineral content rises with body size, since a larger skeleton simply has more bone to hold mineral. Two healthy adults of the same sex can differ by a kilogram or more, mainly because of height and frame, so a tall man near the top of the range and a petite man near the bottom can both be perfectly normal. That is why clinics lean on density, which adjusts for bone size, when judging whether bone is thin.

If your number falls below the typical range for your sex, treat it as a prompt for a conversation, not a diagnosis, since many small-framed healthy people sit there. If your report came from a gym or wellness scan, ask whether a clinical bone-density scan is worthwhile for you, especially if you have risk factors such as a past fracture or long-term steroid use.

How a DEXA Scan Measures Bone

DEXA (or DXA) stands for dual-energy x-ray absorptiometry. The scanner passes a high-energy and a low-energy x-ray beam through the body.6National Center for Environmental Health. Facts About Bone Density (DEXA Scan) Bone, fat and muscle each block the two energies differently, so the machine can sort every pixel into fat, lean tissue or bone mineral.7Scintica. Dual Energy X-Ray Absorptiometry How Does it Work? For bone health, doctors usually scan the hip and the spine.8National Center for Environmental Health. Facts About Bone Density (DEXA Scan)

A session takes about 7 minutes.9BodySpec. How Much Do Your Bones Weigh? Average Human Skeleton Weight Explained The radiation dose is tiny.10BodySpec. How Much Do Your Bones Weigh? Average Human Skeleton Weight Explained For most people that is not a reason to avoid a scan their doctor recommends.

On scan day you lie still on a padded table while an arm passes over you. You usually stay in regular clothes but take off metal such as zippers and belts. There are no needles and no tunnel, and you can leave right afterward. If you recently had a barium test or a contrast scan, tell the technician, since it can disturb the reading.

The technician positions you, often with your legs supported on a block for the spine scan so the lower back lies flat. You may be asked to hold your breath briefly, because movement blurs the picture.

A few things can throw off a reading. Metal in the scan area, such as underwire, can block the beams and distort the image. Calcium supplements that haven’t dissolved can show up on the scan, so ask whether to skip them that day. Spinal arthritis or old compression fractures can make spine density read falsely high, which is one reason the hip is scanned too.

Different brands of scanner can give slightly different numbers, and small changes between scans can fall within normal measurement variation. For follow-up scans, ask to be scanned on the same machine.

Bone Mass Versus Bone Density and Your T-Score

Bone mineral density (BMD), listed in g/cm² on reports, is the mineral divided by the bone area the scanner sees. At the hip, almost all the differences in density between people come from how much mineral they have, not from bone size.11PubMed. Differences in bone mineral density, bone mineral content, and bone areal size in fracturing and non-fracturing women, and their interrelationships at the spine and hip Larger bones are generally stronger because their mineral increases faster than their size.12PubMed. Differences in bone mineral density, bone mineral content, and bone areal size in fracturing and non-fracturing women, and their interrelationships at the spine and hip

Your report’s T-score shows how far your density is from a healthy young adult’s average. A T-score of -1 or above is normal, between -1 and -2.5 is low bone mass (osteopenia), and -2.5 or lower is osteoporosis. The same T-score, however, means a different fracture risk at different ages, and by age 80 a T-score of -2.5 can be lower risk than average for that age.13PubMed. FRAX-based intervention and assessment thresholds for osteoporosis in Iran So many doctors combine the scan with FRAX, a fracture-risk calculator that uses age, past fractures and other risks.14PubMed Central. FRAX- vs. T-score-based intervention thresholds for osteoporosis It is used in more than 100 guidelines worldwide, though countries set treatment cutoffs differently.15PubMed Central. FRAX- vs. T-score-based intervention thresholds for osteoporosis The lowest T-score among the hip and spine sites usually guides the diagnosis, not an average of them, and one site can differ from another, so a report may show a normal hip but a low spine.

You may also see a Z-score, which compares you with people of your own age and sex. Doctors use it mainly for children, younger adults and premenopausal women. A low Z-score can prompt a search for another cause of bone loss.

Most people with osteopenia never break a bone, yet a large share of all fractures happen to people who are not in the osteoporosis range. That is why doctors weigh age, previous fractures, steroid use and family history alongside the number.

FRAX estimates the chance of a major osteoporotic fracture and of a hip fracture over the next ten years. It can be run with your hip density, or without a scan, using only your age, sex, weight and risk factors. Treatment is usually considered when the estimated risk crosses the threshold your country’s guidelines set.

After a low result, it helps to ask which site was lowest, hip or spine, and what your 10-year fracture risk from FRAX is. Ask also whether treatment, retesting or blood tests for vitamin D are advised.

Other Ways to Check Bone Health

A heel ultrasound, sometimes offered at pharmacies or health fairs, uses sound waves rather than x-rays.16PubMed. Prediction of the strength of the elderly proximal femur by bone mineral density and quantitative ultrasound measurements of the heel and tibia Its readings track how strong the hip bone is fairly closely.17PubMed. Prediction of the strength of the elderly proximal femur by bone mineral density and quantitative ultrasound measurements of the heel and tibia Lower heel ultrasound scores signal higher fracture risk even after DEXA results are known.18PubMed Central. Heel quantitative ultrasound (QUS) predicts incident fractures independently of trabecular bone score (TBS), bone mineral density (BMD), and FRAX: the OsteoLaus Study Still, it works as a first screen when DEXA isn’t available, not as a replacement for diagnosis.19PubMed Central. Heel quantitative ultrasound (QUS) predicts incident fractures independently of trabecular bone score (TBS), bone mineral density (BMD), and FRAX: the OsteoLaus Study The heel is not the hip or spine, so it cannot report the T-score used for diagnosis.

If you get a low heel screen, treat it as a reason to ask your doctor about a DEXA scan, and bring the printout to your appointment. A normal heel result doesn’t rule out low spine density.

A newer radiation-free ultrasound method can assess the hip and spine directly.20PubMed Central. Radiofrequency Echographic Multi Spectrometry R.E.M.S. New Frontiers for Ultrasound Use in the Assessment of Bone Status—A Current Picture High-resolution CT scans of the wrist and shin can show bone’s inner structure, mostly in research settings.21PubMed Central. Accuracy of Volumetric Bone Mineral Density Measurement in High Resolution Peripheral Quantitative Computed Tomography DEXA remains the standard because its T-score thresholds define osteoporosis and guide treatment decisions, and most newer methods lack that body of data.

How Bone Mass Changes With Age, Sex and Background

Peak bone mass, the most bone you’ll ever have, is usually consolidated in early adulthood.22PubMed. Causes of low peak bone mass in women Activity, calcium and vitamin D in the teens and twenties raise peak bone mass, leaving more reserve for later loss. Bone is constantly being broken down and rebuilt, and during growth the building side wins. By early adulthood the balance tips toward a plateau, and later toward a slow net loss. Everyone loses some bone with age, so a gradual decline is normal and not a disease by itself.

Around the final menstrual period, falling estrogen drives a faster drop in density.23PubMed Central. Bone Health during the Menopause Transition and Beyond Estrogen restrains the cells that dissolve bone, so when it falls, breakdown outpaces rebuilding. The fastest loss clusters around the last period and the years right after it, then slows. Women who started hormone therapy during the menopause transition lost about 0.4% less density per year.24PubMed Central. Bone Health during the Menopause Transition and Beyond That is modest, and it describes group averages rather than a promise for any one woman. Hormone therapy has other risks and benefits, so it is decided with a doctor and in most cases isn’t prescribed just for bone density. Stopping it later usually allows bone loss to resume.

This timing matters for scans. Women with early menopause or other risks may be scanned earlier than usual, and hot flashes have been linked to lower density, reflecting low estrogen, though they are not a test of bone health.

Even at similar body size, men have more bone mineral and higher density at the hip and shin, though not the spine.25PubMed. Males have larger skeletal size and bone mass than females, despite comparable body size Black adults on average have higher hip and spine density and stronger bones than White adults.26PubMed. Bone mass, microarchitecture and strength are influenced by race/ethnicity in young adult men and women Density varies more within any ethnic group than between groups,27PubMed. Ethnic differences in bone mass–clinical implications so your own scan matters more than averages for your background.

What Lowers Bone Mass and What Helps

Steroids, acid-reducing proton pump inhibitors, SSRI antidepressants, some seizure drugs, heparin and some cancer drugs can harm bone.28PubMed Central. Medication-induced osteoporosis: screening and treatment strategies Breast-cancer aromatase inhibitors push estrogen very low and can cause bone loss.29Osteoporosis Canada. Medications that can Cause Bone Loss, Falls and/or Fractures Hormone therapy for prostate cancer lowers density most in the first year.30Osteoporosis Canada. Medications that can Cause Bone Loss, Falls and/or Fractures Long-term Depo-Provera injections lower density, but most of it returns after stopping.31Osteoporosis Canada. Medications that can Cause Bone Loss, Falls and/or Fractures

If you take one of these long term, ask whether you need a bone scan, and don’t stop a medicine on your own. Most of these drugs treat serious conditions, and stopping could do more harm than any bone loss. Ask whether your dose and duration put you in a group that should have a baseline scan. Bone-protecting steps, such as adequate calcium and vitamin D, weight-bearing activity and sometimes bone-specific treatment, can be added while you continue the medicine.

Vitamin D helps your gut absorb calcium.32Orthopaedics and Trauma. Principles of orthopaedics Parathyroid hormone and vitamin D: from bench to bedside When blood calcium runs low, the body pulls calcium from bone.33Bone Research. Vitamin D, calcium homeostasis and aging So low vitamin D can mean bone is drained to keep blood calcium steady. Prolonged low levels can also leave newly formed bone poorly mineralized and soft. It can weaken muscles and raise the chance of falls too, adding to fracture risk, which is why doctors may check your level when a scan comes back low.

For calcium, dairy, fortified foods and leafy greens are good sources. Sunlight and supplements supply vitamin D, and a blood test can show whether yours is low.

In older adults with osteoporosis, weight-bearing exercise added to treatment raised density more than non-weight-bearing exercise.34PubMed Central. The impact of adding weight-bearing exercise versus nonweight bearing programs to the medical treatment of elderly patients with osteoporosis In healthy women, several months to a year of impact exercise mostly preserved bone rather than adding it.35PubMed. Weight-bearing exercise and ground reaction forces: a 12-month randomized controlled trial of effects on bone mineral density in healthy postmenopausal women Without gravity’s load, astronauts lose about 6% of spine and pelvis bone during flight.36PubMed Central. A systematic review and meta-analysis of bone loss in space travelers

Walking, stair climbing, dancing and strength training load the hip and spine. Swimming and cycling are good for fitness but load bones less. People with osteoporosis should ask about safe impact levels to avoid fractures.

Other everyday things thin bone as well. Smoking and heavy alcohol use are both linked with lower bone density. Being very underweight, including from eating disorders, can reduce bone because of low estrogen and low nutrition. Long periods of bed rest remove the load bone needs.