What does a DEXA tell you about your bones? Why you may need one before menopause! 

It's that time of year again. Time for your annual medical exam. Good for you for monitoring your health! But what about your bones? You may think because you are under 50 that you are not at risk. But getting a DEXA bone scan as early as 30 may be a good idea to establish a baseline score. 

A DEXA is a dual energy x-ray absorptiometry test that measures bone mineral density (BMD). But a DEXA scan only gives you part of the bone picture. Here's the rest of the story you need to know.

First, a few facts. According to the Bone Health & Osteoporosis Foundation, about 54 million Americans have osteoporosis.(OP) and low bone mass (osteopenia). Of those diagnosed, 80% are women. In the age 50+ group, it's estimated that 1 in 2 women and 1 in 4 men will break a bone due to osteoporosis. The most common fractures are in the vertebral spine, wrist and hip. A hip fracture is typically the most serious and impactful on quality of life. These facts alone warrant a good, hard look at bone health earlier rather than later. Are DEXA scans a diagnostic tool that is done too late to be helpful?

Historically, a DEXA scan is scheduled around menopause as that is a peak time women lose bone mass. As a hormone, estrogen helps regulate the cells that break down bones. During the 5-7 years after menopause when estrogen drops, a woman could lose up to 20% of bone mass. By the time a DEXA is performed, bones could be woefully thin. Given that the majority of bone building occurs by age 30, performing a DEXA earlier would provide a baseline picture of bone health. The DEXA could also alert you to a potentially less than perfect bone score to give you years to take positive steps to build more bone before menopause.  If you go through early menopause, it's another reason an early DEXA is warranted. 

Bones are living tissue. Bone growth occurs most rapidly during childhood and slows as you reach your full height. Osteoclasts are special cells that secrete acids and enzymes to dissolve and remove damaged bone and make way for osteoblasts, cells that rebuild and repair bone. This process is called remodeling and continues throughout your life.  When osteoclast activity outpaces osteoblast activity, bones are put at risk for osteoporosis. 

The original DEXA machine was designed by physicist John R. Cameron around 1960 as there was no device to measure bone density and women were dying young of osteoporotic hip fractures. DEXA were further developed in 1987 to today's standard. The scan consists of a large, flat table the patient lies on and an overhead device that moves above the lower spine and hips. This results in a dual image of the two areas considered the best sites to measure BMD. The scan is painless and typically takes less than 15 minutes. But a DEXA leaves out part of the bone picture. 

There are two types of bone tissue. The cortical bone is the hard outer shell that provides structural strength to the hips and long bones of the arms and legs. Trabecular bone is the soft, spongy interior that looks a little like a honeycomb. Trabecular bone is the most metabolically active and changes the most during remodeling. Trabecular bone adds to bone quality and strength when force is applied. Of note, there is a lot of trabecular bone in the spine, making vertebral fractures the most common osteoporotic fracture. 

Bone quality is a key determinant of fracture risk. A DEXA scan measures bone density or how much bone mineral content is present. But a "normal" bone density score  does not always mean strong bones as quality includes the internal trabecular bone architecture which a DEXA does not measure. So when you look at your T-score, it could be the same BMD from year to year but your fracture risk may have increased due to loss of trabecular bone.

What's in a DEXA score? The World Health Organization (WHO) determined the T-Score based on a database of values for bone mineral density of 30 year olds when compared to your DEXA results. A T-score value of -2.5 establishes a diagnosis of osteoporosis for those aged 40-90. The Z-score is a numeric value calculated by comparing BMD to that of a database of people your own age and gender, often used for those under age 40. There is another WHO developed calculator online, the FRAX, a Fracture Risk Assessment Tool. This tool looks at your risk of having a fracture in the next 10 years based on your age from 40-90, BMD, health factors and family history. It is free and easy to use, too. Although not diagnostic, it offers useful information.

Besides a DEXA, there are a few tests which. may help give clues to your bone's ability to remodel. Blood tests include vitamin D, calcium and a magnesium red blood cell tests. Checking for secondary conditions which affect bones such as thyroid, kidney and parathyroid levels. Looking at bone turnover markers with blood and urine tests to see if bone is breaking down more than it is rebuilding. Your health care provider may order these tests even before a DEXA to help determine your bone health. 

While an early baseline DEXA may be one step in looking at your bone health, lifestyle habits also contribute over time.Alcohol interfere with bone remodeling by stimulating osteoclast activity. A sedentary lifestyle does not challenge bones to get stronger and denser. Exercise like strength training positively impacts bone building via weight lifting, push-ups and pull-ups. Making sure you get the nutrient building blocks of calcium, magnesium, vitamin D3, boron and vitamin K. Each play a supporting role to bone building. A lot of bone remodeling is done while you sleep so make sure you get your ZZs, too. 

When it comes to bone health, a DEXA helps you know your number but waiting for one until you are 40 or 50 may be too late to avoid a diagnosis of OP. It is up to you to take care of the bones that take care of you!  

For more on how calcium and other nutrients play a role in bone health, read Bone Building 101: Finding the Right Formula for Stronger Bones.

©TyH, Inc (M. Squires)  For informational purposes only.