Bone health is a serious consideration for older adults, particularly for women following menopause, as the risk of bone fracture increases with age. To assess the strength of the skeleton, doctors measure Bone Mineral Density (BMD), which is the amount of mineralized tissue present in a certain volume of bone. This measurement is most often obtained through a specialized X-ray procedure called a Dual-Energy X-ray Absorptiometry (DEXA) scan. The primary metric derived from this scan, used to diagnose conditions like osteoporosis, is the T-score.
Understanding the T-Score
The T-score is a standardized value that represents a patient’s bone density compared to the peak bone mass of a healthy young adult. It compares the measured BMD to the average BMD of a 30-year-old of the same sex and ethnicity, which is the reference standard for peak bone strength. A T-score of 0 indicates the BMD is identical to this young adult reference mean.
The T-score is measured in standard deviations (SD); each unit below zero signifies a decrease in bone density. A negative T-score means the patient’s bone density is lower than the young adult reference. This measurement is the established tool for classifying bone health in postmenopausal women and men over the age of 50.
The Z-score, conversely, compares a patient’s BMD to the average BMD of a person of the same age, sex, and body size. While the T-score is used for diagnosis, the Z-score can help determine if the bone density is unusually low for that age group. A very low Z-score may suggest that factors other than normal aging, such as an underlying medical condition, are contributing to bone loss.
Expected T-Score Ranges for a 70-Year-Old Woman
For a 70-year-old woman, the average T-score is typically in the osteopenic range due to the natural progression of bone loss after menopause. Studies have suggested that the mean T-score for women in the 70 to 74-year age bracket is around -1.69 at the hip, although this can vary significantly depending on the site measured. This numerical range reflects a BMD that is lower than the young adult peak, but not yet at the level defined as osteoporosis.
Bone density naturally begins to decline rapidly in women during the years immediately following menopause, primarily due to the sharp drop in estrogen levels. The speed of this loss slows down over time, but the cumulative effect by age 70 places many women into a lower bone density category. This expected decline is influenced by a combination of genetics, pre-existing health conditions, and long-term lifestyle factors.
Individual T-scores can be highly variable; a woman who achieved a very high peak bone mass in her youth may score better at age 70 than one who did not. While the average score falls within a specific range, a woman’s true score depends on her unique medical history. This variability underscores the importance of a personalized risk assessment.
Interpreting Clinical T-Score Categories
The World Health Organization (WHO) has established clear numerical cutoffs for T-scores to standardize the diagnosis of bone density conditions in postmenopausal women. A T-score of -1.0 or higher is considered normal bone density, indicating the BMD is within one standard deviation of the young adult mean. Individuals in this category have the lowest risk of fracture.
A T-score that falls between -1.0 and -2.5 is classified as osteopenia, which represents low bone mass. This condition signifies that bone density is reduced, increasing the risk of fracture compared to a normal score. Management at this stage often focuses on preventative measures to stop further bone density decline.
Osteoporosis is diagnosed when the T-score is -2.5 or lower, meaning the bone density is two and a half or more standard deviations below the young adult mean. This diagnosis indicates significantly weakened bone structure, substantially raising the risk of a fragility fracture, particularly in the hip and spine. The presence of a fragility fracture, regardless of the T-score, is often sufficient for a clinical diagnosis of severe osteoporosis.
To fully evaluate a person’s fracture risk, healthcare providers often use the Fracture Risk Assessment Tool (FRAX). This tool integrates the T-score with several other factors, including age, body mass index, personal and family history of fractures, and other medical conditions. FRAX calculates the 10-year probability of a major osteoporotic fracture, providing a more detailed picture of risk than the T-score alone.
Maintaining Bone Health After a DEXA Scan
Regardless of the T-score outcome, several non-pharmacological steps can be taken to promote bone strength. Adequate daily intake of calcium and vitamin D is necessary to support bone remodeling. Women over 50 generally need 1,200 milligrams of calcium and 800 to 1,000 International Units (IU) of vitamin D each day. While dietary sources are ideal, supplements may be recommended to meet these requirements.
Regular physical activity is another method for maintaining bone density, particularly weight-bearing and muscle-strengthening exercises. Activities like walking, jogging, dancing, and lifting weights place stress on the bones, which stimulates the creation of new bone tissue. These exercises also help improve balance and coordination, thereby reducing the likelihood of falls that can lead to fractures.
For women diagnosed with osteoporosis, or those with osteopenia who have a high fracture risk determined by FRAX, pharmacological treatment may be prescribed. Bisphosphonates are a common first-line medication that slows down the cells that break down bone tissue, helping to preserve existing density. Other options, such as anabolic agents that stimulate bone formation or denosumab, may be used depending on the condition’s severity and individual patient needs.