Type 2 diabetes is usually associated with blood sugar, heart disease and kidney problems, but it can also affect the risk of broken bones.
Strangely, people with diabetes may have bones that appear relatively dense on medical tests while still being more likely to experience fractures.
Researchers have been trying to understand this contradiction for years. A new study published in Diabetes Care tested whether people with type 2 diabetes simply lose important parts of their bone structure faster as they grow older.
It drew on participants from the Framingham Study, one of the best-known long-term health research projects in the United States.
Healthy bone has a complicated design. The hard outer shell provides stiffness and protection, while the inside contains a delicate network of small supporting structures.
Scientists call the outer layer cortical bone and the inner network trabecular bone. Both can change with age, and damage to either may reduce the ability of a bone to withstand a fall or other sudden force.
Most people are familiar with bone density tests used to diagnose osteoporosis. These tests are very useful because low bone mineral density is strongly linked with fracture risk in the general population.
However, diabetes does not always follow that familiar pattern. People with type 2 diabetes can have normal or high bone density, meaning a standard scan may make their bones look stronger than their actual fracture history suggests.
Lead author Alyssa B. Dufour and colleagues wanted to investigate what was happening beneath that simple density measurement. Dufour is an associate scientist at the Hinda and Arthur Marcus Institute for Aging Research at Hebrew SeniorLife and an instructor at Harvard Medical School and Beth Israel Deaconess Medical Center.
The researchers used a specialized imaging device that can examine bone in much finer detail than a routine density measurement. It allowed them to study the hard outer bone, the sponge-like inner bone and estimates of bone strength.
They then looked at how these measurements changed over time. The researchers expected that older adults with type 2 diabetes might show faster damage to their bone structure.
That would have provided a fairly straightforward explanation for the higher fracture rate. Faster loss of bone quality or strength could make bones more vulnerable even if their overall density initially looked good.
But the results did not support that simple idea. Older adults with diabetes and those without diabetes showed similar levels of bone loss over time.
The finding means researchers must continue looking for other explanations. Senior author Elizabeth Samelson said the combination of denser bones and greater fracture risk shows that bone density by itself does not capture everything that determines whether a bone will break.
One possibility is that diabetes changes the material quality of bone in subtle ways. Years of elevated blood sugar may alter proteins such as collagen, an important part of the framework that helps give bone flexibility and strength.
These changes may not be fully visible on standard bone scans. A bone could therefore contain plenty of mineral while still having weaknesses that affect how it responds to stress.
Fracture risk also depends on more than the skeleton. People with long-term diabetes may develop nerve damage in their feet, poor eyesight, reduced muscle strength or other problems that increase the chance of falling.
Falls are especially important in older adults because even a relatively strong bone can break when enough force is applied. Preventing falls can therefore be just as important as measuring bone density.
Diabetes treatments and other medicines may also matter. Older patients often have several medical conditions at the same time, and some medicines or illnesses can affect balance, blood pressure, muscle function or bone health.
The new study has useful strengths. It examined detailed bone measurements over time, giving researchers a better view of aging-related change than a study that compares people at only one moment.
Still, it does not provide the final answer to the diabetes fracture puzzle. Similar rates of bone loss do not mean that the bones of people with and without diabetes are identical in every way.
Other aspects of bone quality may not have been captured completely by the measurements used. The number and characteristics of participants can also affect how widely the findings apply, so additional studies in other populations will be important.
The research should not be interpreted to mean that people with diabetes do not need to think about bone health. Instead, it suggests that doctors may need to look beyond the usual assumption that lower bone density is the main route to fractures.
For older adults with type 2 diabetes, a fuller assessment may eventually include bone density together with diabetes control, previous falls, vision, balance, muscle strength, nerve problems and other health conditions. This broader approach reflects how fractures actually happen in real life.
The study’s most important contribution is that it challenges a tempting explanation. The higher fracture risk in type 2 diabetes does not appear to result simply from faster age-related loss of the bone features measured by the researchers.
That leaves an important scientific mystery, but it also gives researchers a clearer direction. Future work can focus more closely on bone material quality and on the many diabetes-related factors outside the bone that may turn a fall into a serious fracture.
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Source: Hebrew SeniorLife
