Human bone density, also referred to as bone mineral density (BMD), measures the amount of bone mineral present in bone tissue. This metric serves as an indicator of skeletal strength and bone health. Healthy bone density allows bones to support the body’s structure and withstand daily stresses without breaking. Maintaining adequate bone density is a lifelong process that directly impacts mobility and quality of life.
Understanding Bone Density
Bone density quantifies the concentration of minerals, primarily calcium and phosphorus, within bone. These minerals contribute to bone strength and resistance to fractures. Bones are dynamic tissues that undergo continuous remodeling, a process where old bone is broken down and new bone is formed.
During childhood and adolescence, bone formation outpaces bone breakdown, leading to increased bone density. Most individuals achieve their peak bone mass around 25 to 30 years of age. After this peak, a gradual decline in bone density begins around age 35, with an estimated loss of 0.3% to 0.5% per year. When bones lose too much mineral density, their internal honeycomb-like structure develops larger holes and thinner outer walls, which can increase the risk of fractures.
Assessing Bone Density
The primary method for measuring bone density is a Dual-energy X-ray Absorptiometry (DEXA) scan, also known as a bone density scan. This non-invasive procedure focuses on areas like the lumbar spine and hip. The scan uses low-dose X-rays to measure the mineral content in these bones, taking about 10 to 20 minutes.
DEXA scan results are reported using T-scores and Z-scores. A T-score compares an individual’s bone density to that of a healthy 30-year-old adult of the same sex and ethnicity. Normal bone density is indicated by a T-score between +1 and -1. A score between -1.0 and -2.5 suggests osteopenia, or low bone mass. A T-score of -2.5 or lower indicates osteoporosis.
Z-scores compare bone density to the average density of people of the same age, sex, and body size. They are used for children, younger adults, and premenopausal women.
Factors Influencing Bone Density
Numerous factors, both unchangeable and controllable, influence an individual’s bone density. Non-modifiable factors include age, as bone density naturally decreases after peak bone mass is reached around age 30. Gender also plays a role, with women having lower bone tissue than men and experiencing more rapid bone loss, particularly after menopause due to declining estrogen levels. Genetic predisposition accounts for an estimated 60% to 80% of the variation in peak bone mass. Ethnicity can also influence bone density, with people of White or Asian descent having a higher risk of osteoporosis.
Modifiable factors offer opportunities to support bone health. Nutritional intake, including sufficient calcium and vitamin D, is important for bone formation and maintenance. Physical activity, particularly weight-bearing exercises like walking, jogging, or dancing, and resistance training, stimulates bone growth and helps maintain density. Lifestyle choices such as smoking and excessive alcohol consumption can negatively impact bone density and increase fracture risk. Certain medical conditions, including thyroid disorders, celiac disease, and rheumatoid arthritis, along with some medications like corticosteroids, can also contribute to bone loss.
Maintaining Healthy Bone Density
Maintaining healthy bone density involves adopting a combination of beneficial dietary and lifestyle habits throughout life. Adequate calcium intake is fundamental, with recommended daily allowances around 1,000 milligrams for adults aged 19 to 50, increasing to 1,200 milligrams for women over 50 and men over 70. Good sources include dairy products, leafy green vegetables like spinach and kale, fortified foods, and certain fish such as salmon and sardines.
Vitamin D is equally important as it aids in calcium absorption. Adults need 600 to 800 international units (IU) per day. Sunlight exposure helps the body produce vitamin D, and dietary sources include oily fish like salmon and mackerel, as well as fortified milk and cereals. Regular physical activity, especially weight-bearing exercises (e.g., brisk walking, jogging, dancing) and resistance training (e.g., weightlifting, using resistance bands), helps strengthen bones and slow bone loss. Avoiding tobacco use and moderating alcohol intake also contribute to preserving bone density.
Conditions Related to Low Bone Density
Low bone density can lead to specific health conditions that increase the risk of fractures. Osteopenia refers to bone density that is lower than normal for a person’s age but not yet severe enough to be classified as osteoporosis. It is considered an early warning sign, indicating an increased risk of developing osteoporosis and fractures.
Osteoporosis is a more severe condition characterized by reduced bone density and structural changes that make bones weak and fragile. This disease progresses slowly and is diagnosed only after a fall or minor impact results in a fracture. Common sites for these fragility fractures include the wrist, hip, and spine. Untreated low bone density, particularly in the spine, can lead to a stooped posture and long-term pain.