Healthy Living

What is Bone Density?

What is Bone Density?

Key Takeaways

  • A bone density test helps to determine whether you have normal bone density, low bone density or osteoporosis
  • The most widely used bone density test is dual–energy X-ray absorptiometry (DEXA/DXA) that measures the specific bone or bones of the spine, hip and wrist and compares these measurements with an average index based on age, sex and size.
  • The results of the bone density test are scored by the T-score and Z-score wherein negative scores indicate lower bone density, while positive scores indicate higher bone density.

For good health, strong bones are important. Bone mineral density(BMD) is the best way to measure the health of the bones. It is a comparison of the person's bone density or mass to that of a healthy person who is of the same age and sex. Bone mineral density can show whether a person has osteoporosis, risk for breaking bones and whether the osteoporosis treatment is working.

Bone density or bone mineral density is the amount of bone mineral in the bone tissue. Bone density measurements are used in clinical medicine as an indicator of osteoporosis, a disease that makes your bones weak, and increases the risk of fractures. It can also indicate your response to treatment for osteoporosis. Bone density is measured in a bone mineral density(BMD) test. It is utilized to calculate standard deviation from the score of the young, healthy population. When referenced in this manner, it is called the T-score. It is also important to note that a Z-score is used to compare a person's current bone densities to their normal bone densities. For instance, if the score is negative 2, the bone density is below normal at that particular age.

Bone mineral density concept is of mass of mineral per volume of bone. The bone density is used clinically to indicate conditions such as osteoporosis and fracture risk. This measurement is done by densitometry. It is often performed in the radiology or nuclear medicine departments of hospitals. The testing is painless and non-invasive. It also involves low radiation exposure. The testing is mostly done over the lumbar spine and the upper part of the hip. If the hip and lumbar are not accessible, then the forearm may be scanned.

Low bone mass that is not categorized as osteoporosis is sometimes known as osteopenia. Causes of osteopenia include family history, not good bone mass when young and certain other conditions or certain other medicines. Those who have low bone mass are at a higher risk of developing osteoporosis. A person who has low bone mass should eat foods rich in calcium, vitamin D, do weight bearing exercises such as walking, dancing or playing tennis. The doctor may prescribe medicines to prevent osteoporosis.

What are the Levels of Bone Density?

World Health Organization (W.H.O.) categorizes BMD into the following levels:

  • Normal: This is a hip BMD that is greater than the lowest limit of normal, and it is taken as one Standard Deviation (SD) below or above the young adult reference mean.
  • Low bone mass: This is also called osteopenia and is defined as a hip BMD that is between one and 2.5 SD, but below the young adult reference mean score.
  • Osteoporosis: W.H.O defines osteoporosis as a hip BMD of around 2.5 SD that is also more or below the standard young adult reference mean score. The greater the negative number, the more severe the osteoporosis.
  • Severe osteoporosis: This is generally a hip BMD of 2.5 SD. It can also be defined as a hip score that is below the young adult reference mean score, and there have been one or more fragility or osteoporosis fractures.

Bone density is usually measured using a number of investigative tests. However, it is can also be calculated using a dual-energy X-ray absorptiometry (abbreviated as DEXA/ DXA).

Epidemiology

  •  England and Wales account for 2+ million women who have osteoporosis.
  •  England and Wales have registered 180,000 fractures annually as a result of osteoporosis.
  •  It has been estimated that 1 in every 3 women and 1 in every 5 men will experience an osteoporotic fracture in their lifetime.

Bones usually deteriorate as one gets older, and this can be accelerated in women by the onset of menopause. Generally, osteoporosis is an age-related disease. It happens because in healthy individuals, the formation of bone exceeds absorption, but the process is reversed by a person's third decade of life in osteoporotic patients. It is a bone disease which occurs when the body loses too much bone, makes too little bone, or in some cases both. As a result, bones become weak and may break from minor falls or, in serious cases, from sneezing and minor bumps.

Low bone density

This is when the bone density is lower than normal, but it is not low enough to be considered as osteoporosis. But such a person has greater risk of developing it. Such people are more likely to break a bone compared to people having normal bone density.

  • Detecting low bone density - to determine low bone density, a bone density test is done. This test is done to check whether you have normal bone density, low bone density or osteoporosis. Low bone density may still be considered normal for some people since some people never have normal bone density for reasons such as genetics, body size, certain diseases or conditions. If you have low bone density, the doctor may suggest taking osteoporosis medicine. Talk to your doctor about its risks and benefits. The online fracture risk assessment tool, FRAX, can be used. This helps to estimate the chances of breaking a bone within the next ten years. It also helps to decide whether you might benefit form taking medications.

Testing

Testing is not necessary for people without any risk factor for weak bones. The primary considerations are:

  • Females of age 65 or over
  • Males of age 70 or above
  • People over age 50 and with any of the following problems such as previous bone fracture, rheumatoid arthritis, low body weight, parent with a hip fracture
  • Vertebral abnormalities
  • Primary hyperparathyroidism
  • History of eating disorders
  • Other conditions are smoking habits, drinking habits, prolonged use of corticosteroid drugs and vitamin D deficiency

Types of Tests

Usually, the different types of tests are non-invasive and they differ depending on which bones are measured.

The tests include:

  • Dual-energy X-ray absorptiometry
  • Dual X-ray absorptiometry and laser technique
  • Quantitative ultrasound
  • Quantitative computed tomography
  • Single photon absorptiometry
  • Dual photon absoprtiometry
  • Digital X-ray radiogrammetry
  • Single energy X-ray absorptiometry

The most widely used is dual–energy X-ray absorptiometry, but quantitative ultrasound has been found to be cost-effective to measure bone density. The DXA measures the specific bone or bones of the spine, hip and wrist and then these measures are compared with an average index based on age, sex and size. The results are important for determining risk for fractures and osteoporosis stage of an individual.

Interpretations

Generally, the results are scored by the T-score and Z-score. Negative scores indicate lower bone density, while positive scores indicate higher bone density.

  • T-score - It is relevant for osteoporosis. It is a comparison of the patient's BMD to that of a healthy person. WHO recommends using the data for a 30-year old white female for everyone, whereas the U.S standard is to using it for 30 year old of the same ethnicity and sex.The criteria are:
    • -1.0 or higher is a normal T-score
    • Between -1.0 and -2.5 defines osteopenia
    • -2.5 or lower defines osteoporosis means a low bone density
  • Z-score - The results are compared to the age-matched normal. It is usually used in severe cases of osteoporosis. It is useful when the score is less than 2 standard deviations below this normal. It helps to scrutinize coexisting illnesses. Also, it helps to scrutinize treatment which may contribute to osteoporosis such as glucocorticoid therapy, hyperparathyroidism or alcoholism.

Limitations

Size of the patient's bone, thickness of the tissues overlying the bone and other factors can affect the measurement. For some populations, reference standards are unavailable for many methods. If the vertebra is crushed, it may result in false high bone density.

Bone density is proxy measurement for bone strength. Bone strength is the resistance of the bones to fractures. It is a truly significant characteristic. Although bone density and bone strength are related, sometimes bone density is a poorer indicator of bone strength.

What are the Risk Factors for Fragility Fractures?

One of the chief risk factors for fragility fractures is a reduction in bone mass density. Likewise, there are a number of other factors that can increase the risk of developing bone/fragility fractures. Some increase the risk of getting osteoporosis, while others are merely independent factors. Therefore, it’s important to identify these risk factors for proper diagnosis and treatment.

Below are some of the risk factors contributing to the occurrence of fractures: 

  • Age is an important factor. As you get older, you are more likely to develop fractures due to low bone mass density.
  • Females are at a higher risk of developing this than men, because they suffer from a lower BMD.
  • If your body mass is below 19 kg/m2, and/or you suffer from anorexia nervosa, your risk of experiencing fractures becomes higher.
  • Another risk factor is your family history. If your parents have experienced a hip fracture, then you are more likely to experience a similar fracture yourself.
  • If you have had a past history of fragility fractures, such as ones related to hips, wrist, or the spine, then you are at a higher risk of experiencing future recurrences of the fractures.
  • If you are on a corticosteroid therapy, which is the taking of oral doses of medicines for three months or more, then the chances of you having fractures is increased.
  • People who have the Cushing’s syndrome are at a higher risk of getting fractures.
  • Alcohol is related to having adverse effects on many diseases. A similar effect is also true for fragility fractures. Alcohol consumption of more than three or more units per day puts you at an increased risk of fractures.
  • Similar to alcohol, smoking has also been known to be a risk factor for fractures. The quantity and frequency of smoking have been known to be linked to a higher risk of developing fractures.
  • Falls and other conditions increase the risk of fractures. This is due to the following reasons:
    • Visual impairment caused by falls
    • Lack of muscle strength or neuro-muscular coordination
    • Cognitive impairment that can be caused by falls
    • Sedative medication and alcohol which can lead to increased risk of falls

Apart from the above, there are many secondary causes of osteoporosis. These are:

  • Rheumatoid arthritis
  • Other inflammatory arthropathies
  • Persistent immobilization or living a very sedentary lifestyle
  • Primary hypogonadism (occurs in both men and women)
  • Primary hyperparathyroidism
  • Post-transplantation of organs
  • Suffering from a chronic kidney disease
  • Suffering from a gastrointestinal disease such as Crohn’s disease, Ulcerative colitis, or Coeliac disease
  • Untreated premature menopause or prolonged secondary amenorrhea also lead to a higher risk
  • Type 1 Diabetes mellitus
  • The presence of a chronic liver disease
  • The presence of a chronic obstructive pulmonary disease

 It has been found that other than aromatase inhibitors and androgen deprivation therapy, other pharmaceutical agents are also responsible for increasing the risk of developing fragility fractures. These include:

  • Proton pump inhibitors (PPIs)
  • Enzyme inducing anti-convulsants
  • Long term use of anti-depressants
  • Anti-diabetic therapy that includes the use of thiazolidinediones
  • Long term use of depot medroxyprogesteroneacetate

How to increase Bone density

  • Consume plenty of calcium - It is the most abundant mineral in our body, found in bones and teeth. Getting adequate calcium will help grow and maintain healthy bones and maintain bone density. The recommended intake varies. It depends on the age and sex of a person. Men over 70 and women over 50 should get 1200 mg calcium per day. Men under 70 and women under 50 should get 1000 mg calcium. Pregnant or lactating women should get 1300 mg calcium per day.
  • Vitamin D - It helps our body to absorb calcium. It is also an important component in bone rebuilding. People over the age of 70 should get at least 800 IU of calcium daily and people under the age of 70 should get at least 600 IU of vitamin D daily.
  • Magnesium - It is an important mineral of our body. Almost 50-60% of magnesium is present in our bones. Adult males should get 400-420 mg of magnesium daily and women should get at least 310-320 mg per day.
  • Vitamin B - People with deficiency of vitamin B12 have more chances of bone fractures and rapid bone loss, since vitamin B12 helps reduce the number of osteoblasts.
  • Vitamin C - It can help increase bone density especially in postmenopausal women. Adult men should get at least 90 mg per day and women should get at least 75 mg per day.
  • Vitamin K - It not only increases bone density, but may also reduce the risk of fractures. Adult males need 120 mcg per day and women need 90 mcg per day.
  • Vitamin E - It has antioxidant and anti-inflammatory properties. Adults need 15 mg per day.
  • Monitor caffeine and alcohol intake - It has been studied that some caffeinated beverages may be associated with bone loss. Excessive intake of alcohol is also bad for the bones.
  • Exercises - Weight bearing exercises build stronger and denser bones.  Pulling action of the muscles helps build bone tissue since the muscle are attached to the bones.
  • Stop smoking - Smoking is associated with higher risk of osteoporosis. It interferes with the ability of the body to absorb minerals and nutrients. Hence, it is linked to low bone density.

Final Thoughts

Bone density is a very important factor, and it should be monitored if low bone density is found to be a problem.

To know more about bone density, go to a medical professional. It is always better to get expert advice rather than getting it from someone you know. So if you feel like you need to know more about your bone density, don’t hesitate to go to the doctor.