Bone mass, often referred to as bone mineral density (BMD), represents the amount of bone mineral present in bone tissue. It indicates bone strength and density, providing the skeletal system with the necessary integrity to support body weight and facilitate movement. This living tissue undergoes continuous renewal, with old bone being broken down and replaced by new bone.
Assessing Bone Mass
The primary method for assessing bone mass is a Dual-energy X-ray Absorptiometry (DEXA or DXA) scan, which is a quick, non-invasive X-ray procedure. This scan measures the calcium content within skeletal tissue, typically focusing on the lumbar spine and the upper part of the hip. The results are commonly expressed as T-scores and Z-scores, which help interpret an individual’s bone density.
A T-score compares an individual’s bone mineral density to that of a healthy 30-year-old adult of the same sex. A T-score between +1 and -1 indicates normal bone density. A score between -1.0 and -2.5 suggests osteopenia, meaning bone density is lower than normal but not yet at the level of osteoporosis. A T-score of -2.5 or lower signifies osteoporosis, indicating significantly reduced bone density and an increased risk of fractures.
A Z-score compares an individual’s bone density to the average bone density of people of the same age, sex, and body size. Z-scores are useful for assessing bone density in children, teenagers, premenopausal women, and men under 50 years old. A Z-score of -2.5 or less may suggest secondary osteoporosis, which is bone loss caused by underlying medical conditions, medications, or lifestyle factors rather than aging alone.
Typical Bone Mass Ranges
Average bone mass varies based on factors like age, sex, and ethnicity. Individuals reach their peak bone mass, the maximum density their bones will achieve, between the ages of 20 and 30 years. After this peak, a gradual decline in bone mass occurs as part of the aging process.
Men attain a higher peak bone mass than women, largely due to having larger skeletons and greater bone width. Women experience a more rapid loss of bone mass around menopause, primarily due to a significant decrease in estrogen levels, a hormone that protects bones. While men do not experience such a rapid decline, their bone loss begins later in life, around age 70, as testosterone levels start to decline.
Ethnicity also plays a role in bone mass, with African-American individuals tending to achieve higher peak bone mass compared to Caucasians. These variations underscore that “average” bone mass is not a single value but rather a range influenced by a combination of demographic and biological factors.
Influences on Bone Mass
Several factors impact an individual’s bone mass throughout their life. Genetics play a substantial role, accounting for an estimated 60-80% of bone mass variation, and a family history of osteoporosis or fractures can increase an individual’s risk.
Nutrition is another important determinant, with adequate intake of calcium and Vitamin D being important. Calcium is the primary mineral component of bone, while Vitamin D facilitates its absorption and utilization. A diet lacking these nutrients can lead to decreased bone density and a higher risk of fractures.
Physical activity, especially weight-bearing and resistance exercises, stimulates bone formation and helps maintain bone density. Conversely, a sedentary lifestyle can contribute to bone loss. Hormonal factors, such as estrogen in women and testosterone in men, also play a role in bone density maintenance, and imbalances can lead to bone loss.
Lifestyle choices influence bone health. Smoking has been linked to reduced bone mass and an increased risk of fractures. Heavy alcohol consumption, particularly during adolescence and young adulthood, can also compromise bone quality, and these effects may not be reversible even if alcohol use ceases.
Supporting Bone Health
Maintaining bone health throughout life involves dietary choices, physical activity, and lifestyle adjustments. Sufficient calcium intake is important, with adults needing around 700 mg to 1,200 mg per day, depending on age. Sources include dairy products like milk, cheese, and yogurt, green leafy vegetables such as broccoli and kale, fortified plant-based drinks, nuts, and fish with edible bones like sardines.
Vitamin D is important for calcium absorption, with adults requiring 10 micrograms (400 IU) to 800 IU daily. While sunlight exposure helps produce Vitamin D, dietary sources like oily fish (salmon, mackerel), egg yolks, and fortified foods (cereals, spreads) are also beneficial. During autumn and winter months, a daily Vitamin D supplement is advisable.
Engaging in regular weight-bearing exercises, such as brisk walking, jogging, dancing, and strength training, helps build and preserve bone density. These activities place stress on bones, promoting their strength. Lifestyle adjustments like quitting smoking and moderating alcohol intake contribute to bone health, as both can negatively impact bone mass.
Regular discussions with a healthcare provider about bone health are recommended. This allows for personalized advice, potential bone density testing, and the management of any underlying conditions or medications that might affect bone mass.