Bones may not get as much respect as our hearts, brains, and other vital organs, but without these rigid parts, we’d be nothing but piles of goo. Our muscles, skin, and other organs literally hang from this skeletal scaffold, giving us form, structure, and the gift of movement.
Type 1 and type 2 diabetes affect bone structure in ways scientists don’t yet fully understand. Although the cause isn’t clear, diabetes raises the risk for fractures. That’s no small thing, as broken bones can lead to permanent disability. Researchers are seeking solutions that can keep people with diabetes on their feet and walking tall.
There are many bone diseases, but the big one is osteoporosis. Some 57 million Americans have osteoporosis, according to the National Osteoporosis Foundation, and about half of women and up to a quarter of men will break at least one bone, often because of osteoporosis. Though the bones in your skeleton may seem as solid and unchanging as stone, they’re in constant flux. Bone is a living tissue that is forever being broken down and then rebuilt, a response to the demands that come with bearing weight day in and day out.
Osteoporosis in adults is caused by an imbalance between bone resorption—the breakdown of bone that transfers calcium to the blood—and bone formation that leaves behind less bone than is normal or healthy. The amount of calcium in the blood is kept within a narrow range for optimal health, and the bones provide a reservoir for this mineral to maintain those levels. Bones are porous, and bigger or more plentiful pores decrease bone density. Lower density makes bones more likely to break.
Doctors diagnose osteoporosis by measuring bone density using dual-energy X-ray absorptiometry (DEXA). “The patient lies down on the table, and the machine measures bone density at the spine, hip, and forearm,” says E. Michael Lewiecki, MD, of the New Mexico Clinical Research and Osteoporosis Center. “The number that comes out of that is the T-score” (left).
According to Lewiecki, all women 65 and older and men 70 and older should have a bone density test. For people at an increased risk for fractures, including those with diabetes, he suggests that postmenopausal women younger than 65 and men ages 50 and older talk to their health care provider about screening.
Not the Same?
While people with diabetes are more likely to experience a bone fracture than those without the disease, the reasons for the increased risk may differ in type 1 and type 2 diabetes. Scientists know that people with type 1 diabetes are at an increased risk for osteoporosis, so it makes sense that they would also be at a higher risk for fractures. A shortage of insulin may be at least partly to blame. “We know insulin is a growth factor. It’s been known to have an effect on stimulating the production and activity of bone-forming cells,” says Michael McClung, MD, founding director of the Oregon Osteoporosis Center. “Kids with type 1 diabetes have low bone growth, which is a major problem,” raising the risk for osteoporosis later on.
With type 2, the explanation for the heightened fracture risk is more mysterious. “The surprise was type 2 diabetes,” says Nelson Watts, MD, director of Mercy Health Osteoporosis and Bone Health Services, because it appears that fracture risk isn’t necessarily related to osteoporosis for people with type 2. Some studies have found that people with type 2 have higher bone densities than average yet are still prone to fractures.
The higher bone densities in people with type 2 diabetes are probably related to the fact that 80 to 85 percent of people with type 2 are overweight or obese. “In the most general sense, higher weight typically translates to higher bone density,” says Elaine Yu, MD, of the Massachusetts General Hospital Endocrine Unit. “Obese patients tend to have larger bones.” Then again, Yu says the standard way of measuring bone density is less accurate in people with extra body fat. So, the bigger question may be whether measuring bone density is a good way to assess fracture risk in people with type 2 or obese people. She says that people with type 2 diabetes and obesity may be at increased risk of fracture at a higher T-score than the general population and may need a revised osteoporosis standard so they can start treatment early enough to prevent fractures.
Blood glucose levels may also affect bone health. Most of the protein inside of bone is collagen, which is susceptible to glycation, the attachment of a glucose molecule to the protein. Higher blood glucose levels lead to more collagen glycation, which may weaken bone structure. “There is a correlation between A1C levels and fracture risk,” with higher A1Cs increasing the risk, says McClung. “That leads some people to think that abnormal [glycation] may be the cause of that relationship.”
Some scientists suspect that diabetes complications, such as nerve disease and peripheral artery disease, may also increase fracture risk by making it more likely that people will fall. In one study, Watts says, “those on insulin with A1Cs less than 7 percent had a greater risk of falling.” That suggests that episodes of
low blood glucose (hypoglycemia) may contribute to fall risk.
The most well-established link between fracture risk and diabetes medications is with the class of drugs called thiazolidinediones (TZDs), such as rosiglitazone (Avandia) and pioglitazone (Actos). Scientists think that TZDs reduce the bones’ ability to repair themselves by discouraging stem cells from becoming bone-repairing cells, which are needed to cope with the bone wear and tear from daily living. “If the little microscopic damage accumulates, that could turn into a real fracture,” says McClung. For people with type 2 diabetes who have other fracture risk factors such as smoking or a history of fractures, American Diabetes Association guidelines suggest avoiding the use of TZDs.
If a routine screening indicates bone loss in the osteopenia or osteoporosis range, it’s time to take action to prevent fractures down the road. Food, exercise, and medications can help keep bones solid.
Food: First, you can start eating for your bones. “Calcium and vitamin D are baseline requirements for bone health,” says Yu, who recommends that postmenopausal women, who are at the highest risk for osteoporosis and fractures, consume 1,200 milligrams of calcium per day and 400 to 800 milligrams of vitamin D.
For calcium, there are plenty of dietary sources. Dairy foods such as yogurt and milk are an obvious choice, especially because healthful low-fat and fat-free dairy products have the same amount of calcium as higher-fat dairy products. Tofu, figs, calcium-fortified orange juice, and broccoli also pack a good dose of calcium.
The evidence on calcium supplements is mixed; some research suggests that taking calcium supplements doesn’t prevent fractures and may increase the risk for heart attacks and death from heart disease if dose levels are too high. Calcium (and vitamin D) needs are different in people with kidney disease. Before you use supplements, discuss these issues with your doctor.
With vitamin D, there are fewer dietary choices. “Fatty fish have vitamin D,” says Yu, but it’s still difficult to get enough from salmon or sardines. Talk to your doctor about checking your vitamin D levels with a simple blood test. That can help determine if you need a supplement and, if you do, the appropriate dose. “Vitamin D supplements are very easy to take and are well absorbed,” says Yu.
Exercise: Weight-bearing activities, such as walking, jogging, and aerobics, can help build or maintain bone density. The research on whether physical activity can directly lower fracture risk is less clear, though some forms of exercise may help with balance and thus reduce the risk for falling. Lewiecki says that studies have shown that tai chi, a low-impact martial art, reduces fall risk. He says, however, that no studies have shown that exercise reduces the risk of fractures in people with diabetes.
Studies suggest that weight loss reduces bone density, which can be bad. But Yu points to a study showing that people who lost weight with a combination of exercise and dietary changes maintained their bone density, while those who lost weight through eating changes alone experienced a loss in bone density. “If you engage in an active exercise during weight loss, you can minimize bone loss,” says Yu.
Medications: Some prescription medications specifically act to shore up bone. “We have medications that will decrease the activity of bone-resorbing cells,” says Watts, so that bones don’t break down as easily during their natural life cycle. The most common of these medications are bisphosphonates. Estrogen, too, is a good choice for some women. Another drug, teriparatide, can stimulate the formation of new bone. Researchers continue to search for new ways to help people with diabetes bone up.