How Does Diabetes Affect Fracture Risk?

Zoe Bond, Dana Li and Rebecca Wills

Diabetes and Fracture Risk

Diabetes mellitus, commonly known as diabetes, is a condition that affects the hormone insulin, resulting in high blood sugar levels. Insulin is needed to absorb glucose (sugar) from the blood to provide energy for cells. In diabetes, there is insufficient insulin to bring glucose out of the blood and into body tissue, and as a result, blood sugar levels are high. People who have Type I Diabetes (T1DM) are not able to make insulin and need insulin injections. Although people with Type II Diabetes (T2DM) are able to make insulin (the levels are actually high), they cannot use the insulin properly and as a result they require medication (either pills or insulin) to lower blood sugar levels.

Diabetes has many effects throughout the body. Abnormal insulin and blood glucose levels can affect the kidneys, nerves, heart, blood vessels and eyes. Diabetes can also have a negative effect on bone, and this means that people with diabetes are at a higher risk of fractures. People with T1DM have low bone density, and almost 20% of people with T1DM who are under the age of 60 have bone density that is low enough to be considered osteoporotic. However, people with T2DM appear to be protected against bone loss, and bone density can be normal. Studies have shown that individuals with T2DM actually have higher bone density than people who do not have diabetes. This suggests that the bone quality, another determinant of bone strength, may be poor and may explain increased fracture risk in T2DM.

In order to calculate a person’s fracture risk, doctors can use an assessment tool that considers risk factors such as: age, height, weight, previous fractures, family history of osteoporosis, personal habits like smoking and alcohol consumption, particular medications, certain medical conditions such as rheumatoid arthritis and results from a bone density scan. However, it is now recognized that current risk assessment tools underestimate fracture risk in people with diabetes and current research is looking at tools that may improve our ability to assess their risk.

Changes in bone density and bone quality are not the only ways that diabetes can increase a person’s risk for fracture. Diabetes can also increase the risk of falls. Falls are more common in people with diabetes because diabetes can lead to complications such as reduced sensation in the feet, reduced vision and increased light-headedness. In addition, if someone with diabetes has low blood sugar (hypoglycemia), they are at increased risk of falling. The combination of more fragile bones and a higher risk of falls increases the risk of fracturing a bone. The bones commonly fractured by people with diabetes include the upper arm, wrist, hip and spine.

Fracture risk is significantly increased in T1DM. Men with T1DM are twice as likely to fracture a bone as compared to men without diabetes. The risk is four times higher in women with T1DM compared to women without diabetes. People with T1DM are also more likely to fracture earlier in life compared to the average person without diabetes. In addition, the longer a person has lived with T1DM, the higher their risk of fracture.

People with T2DM also have a higher risk of fracture. Factors that increase this risk include having T2DM for longer, poor blood glucose control and the presence of diabetic complications such as eye or kidney involvement. Those with T2DM have as much as a 70% higher chance of suffering a non-spine fracture compared to those without diabetes. In addition, many patients with T2DM have low levels of vitamin D, which is needed to keep bones strong.

Diabetes Medications and Fracture Risk

There are many medications available to help control blood glucose levels. Research has shown that some may increase bone strength and reduce the risk of fracture, while others may have a negative effect on bone and increase the risk of fracture. Metformin is thought to be good for bones. Some animal experiments suggest that Metformin has a positive effect on bone health by increasing bone building cells (osteoblasts) and decreasing bone absorbing cells (osteoclasts). Thiazolidinediones (TZDs) have been shown to do the opposite, decreasing the development of cells that build new bone while increasing the number of cells that break down bone. This means a person with T2DM taking TDZs is at a greater risk of fracturing bones because the amount of bone loss is greater than the amount of new bone made. A number of studies have shown that hip fractures are increased in people taking TZDs, and that the risk increases with longer duration of use. Another diabetes medication, canagliflozin (Invokana ®), has also been found to be associated with an increased risk of fracture, although at this time no mechanism has been identified. Many of the medications used to treat diabetes can increase the risk of low blood sugars, which is a risk factor for falls.

What Does This Mean For You?

If you have diabetes, either T1DM or T2DM, you are at a higher risk of suffering a fracture, both because of the effects of diabetes on bone and because of the increased risk of falling. There are many different medications currently used to treat diabetes, and some of these can affect bone health. It is important to speak to your doctor or healthcare practitioner to have a full assessment of your diabetes and bone health. This should include a fracture risk assessment, reviewing diabetes medications to make sure they are right for you, and assessing for risk of falls. Taking part in a regular exercise program that includes balance and strengthening exercises is an excellent way to help maintain your bone density, reduce your risk of falls and fractures, and benefit your overall health.

Zoe Bond, Dana Li and Rebecca Wills are 4th year Kinesiology students at the University of Waterloo (at time of writing). The authors were introduced to fracture risk in those with diabetes mellitus during a course on bone health. They found the topic intriguing and therefore chose to engage in further research. They hope that this article will be informative for those living with both osteoporosis and diabetes.