Saturday, September 3, 2011

Lessons from DXA

In 2003 my doctor recommended that I get a DXA, an imaging procedure that assesses bone mineral density and is used to diagnose osteoporosis.  I was unhappy to learn that my BMD was low (osteopenia) though not yet in the osteoporosis category.  The test takes measurements from the spine and both hips.  In my case the spine was worse; the hip measurements were pretty much normal.  My height was 5’51/2”, the same as it has been since sixth grade.

The numbers for the spine were worrisome because an uncle and an aunt on my father’s side had both experienced serious back problems in old age.  My uncle had back surgery and wound up in a wheel chair for the rest of his life; my aunt just put up with the pain.   My doctor wanted to prescribe a bisphosphonate to help strengthen my bones but I said, “No, thanks.”  Instead, I started taking a lot more calcium and vitamin D and continued my cardio and weight training.  In successive tests, done every two years, the readings stayed about the same.

This year I went for another DXA and was startled to learn that my height was now 5’ even; I’d lost a half inch.  I asked to see a copy of the report, thinking that the reading on my spine would show deterioration.  Instead, the spinal reading was the best it had ever been, up 10% compared with the previous test.  The hip readings were lower but not a lot.  These results raised many questions.  How could I be losing height if my spine was actually better off than it had been?  What had caused the improvement? Why were the hip readings getting lower?

When I got home I asked my husband to measure my height:  the half inch was still gone.  So I went to Google and learned a number of things.  First, a person’s height can vary throughout the day because of gravity and physical activity.  Typically, a person will be tallest in the morning, after eight hours of no vertical pressure on the body, and shortest in the evening.  I thought about the fact that I had been doing push-ups and pull-ups in the morning before the test.  Strength training tends to make muscles tighten up, especially if you don’t stretch afterward. 

Later the same day I spent some time doing back-stretching exercises and had my husband measure me again.  The half inch was back! As to why the spine measurement had improved my best guess is the plyometric exercises I started doing a couple of years ago.  Plyo involves hopping and balancing.  Jumping jacks are an example, as is hopscotch, activities that involve impact on the body.  A study comparing young female soccer players with inactive women found that the soccer players had significantly higher bone density.

What about the lower hip numbers? Google turned up references to a recent study linking wearing a cell phone on your belt with reduced bone density in the hip (see “Bone Density and Cell Phones” above).  My trainer Greg also suggested doing more hip presses and lunges so I will.  A sample of one is not a scientific study but  it seems pretty clear that exercise can go a long way toward maintaining and improving bone density with little expense or risk of side effects. 

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