A T-score is a measurement of bone density. The value shows the difference in a person’s bone mass in comparison with an average healthy 30-year-old. It can reveal a person’s risk of osteoporosis.

The “T” represents a standard deviation either above or below the average score for bone density. T-scores can play an important role in the diagnosis and treatment of osteoporosis. Osteoporosis is a disease of the bone where there is a reduction in bone density and strength. This can increase the risk of fractures.

T-scores show a person how their bone density compares to young, healthy adults. Negative numbers indicate a person has a lower bone density than the average 30-year-old.

Read on to learn more about what a T-score measures and which scores indicate osteoporosis.

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T-scores measure bone density. The “T” represents the number of standard deviations from the average bone density of a healthy 30-year-old of the same sex and ethnicity.

Each deviation represents about 10–12% difference in bone mass. Standard deviation is a mathematical term that people can use to calculate how much a result varies from an average.

A person with the same bone density as an average 30-year-old will have a T-score of 0. A score of 1 means that a person’s bone density is roughly 10% greater than that of the average 30-year-old. A T-score of -1 means a person’s bone density is about 10% less than that of the average 30-year-old.

T-scores come from a bone density test, also known as a DEXA scan, or bone mineral density test. The test measures the quantity of calcium and other minerals present in a specific area of bone.

A healthcare professional will then compare a person’s T-score to see how much it deviates from the score of a healthy 30-year-old.

Higher positive numbers indicate greater bone density, while lower negative numbers indicate reduced bone density. In general, lower negative numbers indicate an increased risk of osteoporosis and fractures.

A negative T-score of 2.5 or lower indicates osteoporosis.

Bone density changes throughout a person’s life. A person will achieve what is known as peak bone mass during their lifetime. Peak bone mass refers to the time when a person’s bones have the most mass.

Prior to this point, genes and lifestyle factors will help increase bone mass. It will often stay steady for a few years before a person starts to lose mass.

Most people reach peak bone mass around the ages of 25–30. After age 40, most people start to lose bone mass. Average bone mass changes that occur throughout different ages include:

Age (years)Bone mass changes
10–20Peak bone mass will depend on factors such as genes, exercise, diet, obesity, and pregnancy.
20–30Bones will typically reach their peak bone mass.
30–50Starting around age 40, bone remodelling will slow and the body will not replace all bone mass, leading to decreasing bone mass.
50–70Biological females have the highest risk of bone loss through menopause, although both females and males require continued calcium supplements to support bone health.
70 plusMost adults will experience bone mass loss and should consider bone density scans if they have not done so already.

The Z-score is similar to a T-score in that it shows a deviation from an average bone density score. However, the Z-score compares a person’s bone mass to peers who are the same age and sex.

For example, a 50-year-old male’s Z-score will compare their bone density to that of other 50-year-old males.

A Z-score is helpful for diagnosing secondary osteoporosis that may occur due to medications or other health conditions. Particularly, a Z-score may be useful for populations such as:

  • children
  • young adults
  • females who are premenopausal
  • males under the age of 50

A low score should prompt a doctor to test for other underlying conditions that may cause bone density loss.

Read on to learn more about Z-scores.

Improving T-scores involves building stronger and denser bones. To do this, a person can take steps such as:

  • eating foods with bone-supporting nutrients, including calcium, vitamin D, and protein
  • avoiding smoking
  • staying physically active, including weight-bearing activities
  • limiting alcohol consumption
  • treating any underlying inflammatory conditions that may contribute to osteoporosis

Osteoporosis can affect anyone as they age. It can also result from other conditions that cause bone density loss. Some people are more likely to develop osteoporosis. Risk factors for osteoporosis include:

  • increasing age
  • history of a broken bone after age 50
  • previous surgery to remove the ovaries before menstruation periods stopped naturally
  • family history of broken bones or osteoporosis
  • smoking
  • altered levels of hormones, such as too much thyroid hormone, too little estrogen in females, or too little testosterone in males
  • poor dietary habits
  • lack of physical activity or prolonged bed rest
  • heavy drinking
  • underweight or low body mass
  • long-term use of certain medications, such as corticosteroids, proton pump inhibitors, or anti-epileptic medications

A T-score represents a standard deviation from the average bone density of healthy 30-year-olds. Health experts can use a T-score value to help determine if a person has osteoporosis, or a lower bone density than they should.

T-scores of -2.5 or less indicate osteoporosis. A person will need to take steps to treat the condition to help improve bone density and reduce their risk of bone fractures.

A person can take steps to improve their bone density. These include eating a bone-healthy diet, taking regular exercise, avoiding smoking, and limiting drinking alcohol.