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Surprise! Bone Density and Bone Strength Aren’t the Same Thing

Bone Density and Bone Strength

All women should be concerned about their bone density and risk of osteoporosis, a serious bone condition where bones become less dense, more fragile, and prone toward breakage. A bone altered by osteoporosis can break with only minor trauma. For example, some women only discover they have osteoporosis after they develop a fracture from something as minor as coughing. Osteoporosis is no joke!  It’s one of the leading health problems in women after menopause. Hip fractures are a major cause of morbidity and mortality in older women. In fact, almost 80% of all hip fractures occur in women. Men can get osteoporosis too, particularly those who are small-boned, but it’s less common.

Are You at Risk of Osteoporosis Even if Your Bone Density is Normal?

Risk factors for osteoporosis include Caucasian or Asian ethnicity being small-boned or underweight, smoking, lack of exercise, certain medications, overuse of alcohol, family history, and some medical conditions. However, you can still develop osteoporosis even if you don’t have these risk factors.  That’s why it’s important to monitor your bone density based on your health care provider’s recommendation. A bone density scan (DEXA scan) is a quick and easy procedure that exposes your body to small amounts of radiation. Based on the scan, you get a T-score that indicates how your bone density compares to the bone density of a healthy 30-year-old adult.

If you get a report that your bone density is in the normal range based on a DEXA scan, you feel reassured and assume your bones are in good shape. However, scientists and health care professionals now realize that dense bones aren’t always strong bones. The quality of a bone and how strong it is matters too and density and bone quality aren’t necessarily correlated.

Bone Structure and Quality: Why Quality Matters

What is bone quality? It’s a measure of how well a bone can resist fracture, independent of its density. If you looked at bone tissue under a microscope, you’d see that it has small pores filled with blood vessels and nerves. In fact, bone has three layers: compact bone, spongy bone, and the inner bone marrow and is made of living cells that build new bone tissue and cells that break down old, damaged bone. That’s why bone must have blood vessels to carry nutrients to these active cells. Bone is hard because of its high mineral content, made up of calcium and phosphorus but it also contains soft, spongy material called collagen. Bone is a complex, living tissue that’s constantly changing as old bone is replaced with new bone. When you’re young, you build more bone than you lose but that shifts with age.

Beyond bone density, other factors impact its susceptibility to breaking. Bone can build up areas of microscopic damage that weaken the bone even when bone density is in a healthy range. Plus, resistance to fracture also relates to the quality of the collagen that makes up the bone. A dense bone isn’t always a strong bone. Here’s an example. At one time, a treatment for osteoporosis was to give patients sodium fluoride. The treatment was successful at increasing bone density. However, it didn’t make the bone less prone to fracture. In fact, it increased fracture risk. Sodium fluoride boosted the density of the bones but didn’t make the bone stronger.

Another clue that bone quality matters is people with similar bone densities can have different rates of bone fracture. So, two people can have a similar T-scores as determined by a bone density scan, yet one develops one or more fractures and the other doesn’t. One individual has better bone quality than the other. Also, as we age, the risk of fracturing a bone increases faster than the rate of bone loss, suggesting that loss of bone strength and quality is an issue.

Age is another important factor that determines bone quality and how strong a bone is. Younger people have stronger bones than older people across all T-scores. Therefore, a young person with a low T-score, indicating low bone density, may still have stronger bones than the T-score would suggest. Likewise, a woman after menopause may have a normal T-score and still have bones that aren’t as strong as they should be. So, bone density, as measured by a T-score, doesn’t measure bone quality and how strong a bone is.

How do you measure bone quality? As of now, there’s no established way to measure bone quality, although researchers are looking at methods such as quantitative CT and high-resolution MRI, but these aren’t practical for most clinical situations.

Exercise Can Improve Bone Quality

How can you improve the quality of your bones? We know that exercise, particularly early in life, can improve bone density, but there’s also evidence that exercise enhances bone quality, independent of density. Most people exercise to increase endurance and muscle strength but doing so may improve the strength and quality of your bones as well. Studies show that resistance training places a mechanical load on the muscle and the bone, thereby improving muscle and bone strength and quality. Therefore, resistance exercise, using a challenging resistance, is one of the best ways to reduce bone loss and preserve bone strength and quality.

The Bottom Line

Your muscles and bones have to last a lifetime and women are at high risk of bone fractures due to osteoporosis. Bone density declines with age but so does bone strength and quality. The best way to mind the health of your bones is to stimulate your bones through exercise, including resistance training. Now you have another reason to strength train! Do it for strong, healthy bones.

 

References:

  • com. “Bone density vs bone quality:What’s a clinician to do?”
  • Postgrad Med J (1991) 67, 323 – 326.
  • Sports Med. 2014 Jan;44(1):37-53. doi: 10.1007/s40279-013-0100-7.
  • Kidney International (2016) 89, 16–19; http://dx.doi.org/10.1016/j.kint.2015.11.004.
  • Baillieres Clin Rheumatol. 1997 Aug;11(3):495-515.
  • Berger-Groch, J., Thiesen, D.M., Ntalos, D. et al. Assessment of bone quality at the lumbar and sacral spine using CT scans: a retrospective feasibility study in 50 comparing CT and DXA data. Eur Spine J (2020). https://doi.org/10.1007/s00586-020-06292-z.
  • Hong AR, Kim SW. Effects of Resistance Exercise on Bone Health. Endocrinol Metab (Seoul). 2018;33(4):435–444. doi:10.3803/EnM.2018.33.4.435.

 

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