DEXA Scan (Dual X-ray Absorptiometry) to Measure Bone Health
How is bone mineral density measured?
Dual X-ray absorptiometry (DXA) is the preferred technique for measuring bone mineral density (BMD). DXA has also been called dual energy X-ray absorptiometry, or DEXA. DXA is relatively easy to perform and the amount of radiation exposure is low. A DXA scanner is a machine that produces two X-ray beams, each with different energy levels. One beam is high energy while the other is low energy. The amount of X-rays that pass through the bone is measured for each beam. This will vary depending on the thickness of the bone. Based on the difference between the two beams, the bone density can be measured.
At present, DXA scanning focuses on two main areas -- the hip and spine. In certain situations -- if the hip or spine can't be measured, for instance -- it is measured in the forearm. Although osteoporosis involves the whole body, measurements of BMD at one site can be predictive of fractures at other sites. Scanning generally takes 10 to 20 minutes to complete and is painless and noninvasive.
How much vitamin D do I need?
In November 2010, the Institute of Medicine's expert committee set a new "dietary reference intake" for vitamin D.
Assuming that a person gets virtually no vitamin D from sunshine -- and that this person gets adequate amounts of calcium -- the IOM committee recommends getting the following amounts of vitamin D from diet or supplements (Note that the IOM's upper limit is not a recommended intake, but what the IOM considers the highest safe level):