The issue: Although bone mineral density is often discussed in relation to post-menopausal women, it is also extremely important for men. Throughout life, bone undergoes a process of remodeling which is a continuous coordinated cycle that includes bone growth and bone removal. From birth until the late 20’s, bone mineral density increases until it reaches a peak. An individual’s peak bone mass is determined by many factors including heredity, sex, race, and lifestyle factors such as calcium, vitamin D, exercise, and smoking. After peak bone mass is reached, a plateau is maintained for some time and then age-related bone loss begins and continues throughout the rest of life. Men lose bone at a rate of 0.5% to 1% per year.
Natural hormonal changes that occur with age (decreased testosterone production by the testes in men) and certain medications such as corticosteroids and androgen deprivation therapy (for prostate cancer) can accelerate bone loss (more) especially during the first year of treatment. The risk of fracture increases with the longer duration of androgen deprivation therapy. Additionally, physical inactivity, and insufficient dietary calcium intake, reduced intestinal calcium absorption, vitamin D deficiency contribute to bone loss. One of the most common causes of low bone mineral density in men is low testosterone (which declines 1 to 3% per year after age 30), and testosterone treatment can be very beneficial (discussed in Healthy Merlin post on testosterone replacement) (more). In short, testosterone therapy may be indicated even in patients without symptoms if bone mineral density is low. The risk of fracture rises exponentially as bone mineral density declines. The importance of increasing bone mineral density is that 18% to 33% of older hip fracture patients die within 1 year of their fracture, and between 25 to 75% of those patients who are independent before their fracture do not achieve the same level of activity within 1 year following their fracture.
Diagnosis: The most effective way to evaluate and monitor bone density is Dual-energy X-ray Absorptiometry (DXA). DXA is a painless and non-invasive radiographic test which evaluates the hip, lumbar spine, and forearm to accurately measure bone mineral density. The goal of the test is categorize a patient’s bone density as normal, low (osteopenic), or osteoporotic. Such assessment of bone density provides an estimate of fracture risk.
Although DXA may diagnose abnormal bone mineral density, it does not determine the cause. A full history, physical, and laboratory testing may be needed to find the cause. Additionally, the 10-year risk of an osteoporosis-related fracture can be estimated using FRAX (WHO Fracture Risk Assessment Tool) is useful online questionnaire to gauge your fracture risk by using the “calculation tool menu” to select your location.
Once the cause is determined, it can often be treated. Although there are many prescription medications for increasing bone density, they do not come without risks. The risk versus benefit must always be weighed by you and your physician.
It is important to note that the radiation dose from a DXA scan (depending on the sites evaluated and the instrument used) is very low and ranges from 0.1 -10 microsieverts which is comparable to the amount of natural background radiation one receives per day (5 – 8 microsieverts/day). Of note, a bone density exam provides far less radiation exposure than a chest x-ray.
There are many different vendors and types of machines to assess bone mineral density. The most important point for patients to know is that serial bone densitometry exams should be ideally performed at the same center on the same machine and if possible by the same technologist to ensure consistency between exams and minimize operator and machine variability.
The bone density measurement in adults is usually reported by a measure called T-score which compares the patient’s bone mineral density to the average young adult’s peak bone density by describing the number of standard deviations above or below the average. DXA is a good measure of medical treatment effect (see below). For example, for men with low bone density and and low testosterone, DXA scans are ideally done at 2 year intervals to ensure that bone density is improving or stable. Click below to see a sample DXA report.
For more details about DXA, see The International Society For Clinical Densitometry (ISCD) http://www.iscd.org.
Treatment: Treatment options are best determined by your physician and these include weight-bearing exercise, vitamin D, calcium, testosterone therapy for men, and bisphosphonates (such as alendronate, risedronate, ibadronate, and more recently zoledronate) especially for men with osteopenia (T-score approaching -2) or osteoporosis and high risk fro future fracture. Risk factors for fracture such as smoking and excessive alcohol intake should be counseled to stop these activities. Recently, a medication which works differently than bisphosophonates, called denosumab, a human monoclonal antibody, has been shown to be effective in reducing bone fractures (more). Other agents such as odanacatib are currently undergong study.
See the following for more information about bone mineral density and aging.
–Brian Wosnitzer, M.D.
March 15, 2013