How Diabetes Affects Your Skeleton
As common as they seem, broken bones are a major health problem. For older people, a broken hip or leg can be a life-altering event, reducing their independence and shortening their lives. About 1.5 million people in the United States have a bone disease–related fracture each year—often involving a hip, leg, or wrist. A disproportionate number of them are people with diabetes.
That may come as a surprise. Bone fractures aren’t commonly discussed as a diabetes-related complication, but over the past decade, researchers and clinicians have increasingly realized that diabetes may weaken bones, upping the risk for breaks. Large-scale studies show that people with diabetes are more likely to break bones, especially as they get older. People with type 2, for instance, are 30 to 40 percent more likely to break a hip in their lifetime than those without diabetes, according to a 2015 study published in the journal Osteoporosis International. For people with type 1, the risk is higher still: They’re 300 to 400 percent more likely to break a hip than someone without diabetes.
Numbers like that are beginning to turn heads in the diabetes care community. “Lots of endocrinologists and primary care physicians don’t think of skeletal fragility as a complication of diabetes,” says Sundeep Khosla, MD, a bone loss researcher at the Mayo Clinic in Rochester, Minnesota. “But bone and skeletal disease ought to be considered another diabetic complication, like nephropathy, cardiovascular disease, or neuropathy.”
Bones are made of minerals, mainly a mix of calcium and phosphorous. Those minerals are threaded through with tiny blood vessels and stabilized with a protein called collagen. Your bones aren’t static. Rather, they’re constantly being remodeled by specialized cells that remove old bone and put new material in place. You get a new skeleton once every seven years, give or take.
Why people with diabetes have more fractures is still an open question. “That’s something we don’t understand, and a topic of research,” says University of California–San Francisco epidemiologist Ann Schwartz, PhD, MPH. Bone research is complicated, particularly when it comes to diabetes: Unlike with skin or even muscle, it’s very difficult to take samples of bone from living patients. Even removing a tiny piece would be painful. (One of the few testing methods involves numbing part of the shin and hitting the bone underneath with a tiny hammer, then measuring the distance the probe indents the bone.) And there’s a lack of techniques that can identify what’s happening with bone blood vessels. Researchers use mice as stand-ins for type 1, but they’re far from perfect equivalents. There’s no good way to mimic type 2 diabetes in mice.
Unable to experiment directly, researchers first look at large-scale studies of people with type 1 and type 2 diabetes to tease out trends. The most obvious possibility might be that people with diabetes are more likely to fall than the general population. Neuropathy, nerve damage that affects the hands and feet, can make walking a challenge, for example. “In population studies, we looked at people with diabetes with fractures,” Khosla says. “When you looked at the relationship of complications to fracture risk, one that popped out was neuropathy.”
But when researchers crunched the numbers, neuropathy and other diabetes-related complications didn’t explain all of the differences in fracture frequency. People with type 1 are known to have lower bone density than people without diabetes, or even people with type 2. But increasingly, Schwartz says, researchers are realizing that people with type 2 diabetes might have weaker bones as well. “It turns out that people with diabetes have an increased risk of all fractures that isn’t related to fall risk,” she says. “That points out the intrinsic difference in the architecture of the bone.”
This, too, is a bit of a puzzle: At first glance, people with type 2 diabetes seem to have bones that have as much mineral in them as people without diabetes—or even more. The most common test doctors use to measure bone health is something called a dual-energy X-ray absorptiometry (DEXA) scan. The procedure measures the density of mineral in the bone and is usually recommended for women over 65 and men over 70. However, the DEXA doesn’t measure things like collagen, the organic material that binds bone mineral together.
Based on DEXA results alone, there’s little difference in the bones of people with type 2 and people without. In fact, doctors often skip bone density measurements for people with diabetes—particularly people with type 2. Based on studies of healthy populations, Schwartz says, doctors assumed people who were overweight or obese, common in type 2, would have stronger, denser bones to support the extra weight. The standard tool doctors use to calculate fracture risk, a computer program called FRAX, doesn’t even include diabetes as a possible factor. “I suspect clinicians aren’t screening as often,” she says. “Now there’s more awareness that fracture risk is higher and this is a group that should have the same screenings as [people without diabetes].”
Factors Behind Fractures
DEXA test numbers don’t tell the whole story. Khosla thinks that when it comes to bone, the issue for people with type 2 diabetes may be one of quality, not quantity. “Normally people with type 2 diabetes have normal or increased bone density,” Khosla says. “But despite having normal bone density, they have an increased risk of fractures, perhaps because the bone quality is poor.” In people with type 1, the fracture risk is even worse, and weak bones may be the problem.
Like many complications of diabetes, there are probably lots of factors at play. Studies suggest that high blood glucose is partly responsible for weaker bones, for example. “Bone material properties were correlated with glycemic control over 10 years. The worse the glycemic control, the worse the bone material quality,” says Khosla. “If all this is correct, better glycemic control should help.”
Another factor could be problems with the tiny blood vessels that feed and help build bone—similar to the blood vessel damage that causes the eye disease diabetic retinopathy. Some diabetes medications—including thiazolidinediones (TZDs) such as pioglitazone (Actos)—are associated with higher fracture risks. Antidepressants, too, are connected with fractures, but it’s hard to know if the medications or the depression they’re treating causes the problem. And finally, there’s evidence that episodes of low blood glucose (hypoglycemia) can hurt bone cells, making them slower at repairing tiny cracks and building up new bone.
At the cellular level, people with diabetes may function differently than people without. “Lower rates of bone remodeling might impair the ability to repair microcracks and make them more vulnerable to fracture,” Khosla says.
People with type 1 face similar challenges, but for much longer periods. Because type 1 often strikes early in life, the ups and downs of blood glucose and other complications happen during a critical time for skeletal development and have many more years to affect bone health. “In type 1, you’re getting all those things together, and it’s happening during growth and development,” Khosla says. “Clinically, you have all of these changes and on top of that have worse bone density and weaker [bone structure].”
Researchers think people reach peak bone mass in their 20s; most people with type 1, then, never reach their full potential bone mass. “Since aging results in gradual loss of bone mass,” Schwartz says, “those with lower peak bone mass are more at risk for developing low bone density as they age.”
Risk Factors for Osteoporosis
Age: After age 30, the body begins to lose bone mass. The older you get, the less you have and the harder you have to work to maintain what’s left.
Gender: Women are four times as likely as men to have osteoporosis.
Family history: If your parents or grandparents fractured a hip after a fall, look out: You may have inherited weaker bones.
Body weight: Heavier people have thicker, denser bones. Thin people are at higher risk for bone mass loss because they have less bone to lose.
Strengthen Your Bones
If your doctor says you’re at greater risk for fracture, it’s possible to take action. “In general, the evidence is that the kind of treatments we use in people without diabetes work just as well in people with diabetes,” says University of California–San Francisco epidemiologist Ann Schwartz, PhD, MPH. Read on for tips for keeping bones strong.
- Know your risk. “Patient awareness is a huge problem, especially in people dealing with other complications,” says Mayo Clinic researcher Sundeep Khosla, MD. Being aware of the fact that diabetes puts you at a higher risk for fractures will help you talk to your doctor about protecting your bones.
- Get a DEXA scan. The most common measurement of bone health, the DEXA scan, is typically recommended for men over 70 and women over 65. But regardless of your results, it’s important to keep in mind that bone density isn’t the only factor in bone health. People with type 2, for example, might have bones that are as dense as people without diabetes, but the bones may still be weaker because of changes in the collagen that binds bone minerals together. “Bone density doesn’t tell you everything that’s going on,” says Schwartz. “It’s important to get a DEXA, but it’s going to underestimate the risk.”
- Manage your blood glucose. Better blood glucose management equals better bone health. “There’s evidence that people with high blood glucose may have higher fracture risks,” says Schwartz. “Poor glycemic control definitely increases the risk of fracture.” Data from studies of thousands of people with diabetes show that when A1C is over 8 percent, there’s a spike in hip fractures.
- Make lifestyle changes. Be sure your diet includes adequate sources of calcium and vitamin D, both critical for building new bone and maintaining what you’ve got. Even if you’re not deficient in the nutrients, it’s smart to get the recommended daily intake (RDI): For anyone age 4 and older, that’s 1,300 milligrams of calcium and 20 micrograms (800 IU) of vitamin D daily. And it might seem counterintuitive at first, but it’s important to stay active. “Exercise tends to reduce the risk of falling. It improves balance and strength,” says Schwartz. Meanwhile, consider revamping your workouts. Weight-bearing exercises, such as jogging or weight-lifting, can help strengthen bones.
- Discuss medication. Because osteoporosis is such a common problem for older adults, there’s been a lot of research into drugs that slow or reverse the deterioration of bones, but they’re generally under-used in older people with diabetes. As the increased fracture risk that people with diabetes face becomes clear, and as researchers develop better measures of risk, the presence of diabetes itself may dictate the use of these medications, even when bone density measurement doesn’t show full-blown osteoporosis.