The growing diabetes epidemic is not limited to people—diabetes mellitus is increasing among dogs as well. Researchers estimate that one in 200 dogs will develop the disease. Fortunately, treatment has made huge strides in recent years, and as a result, dogs with diabetes are living longer, healthier lives.
The mechanism of diabetes is relatively simple to describe. Just as cars use gas for fuel, body cells run on a sugar called glucose. The body obtains glucose by breaking down carbohydrates in the diet. Cells then extract glucose from the blood with the help of insulin, a hormone made by the pancreas in specialized cells called beta cells. (The pancreas, an organ situated behind the stomach, produces several hormones.) In diabetes mellitus, cells don’t take in enough glucose, which then builds up in the blood. As a result, cells starve and organs bathed in sugary blood are damaged. Diabetes is not curable, but it is treatable; a dog with diabetes may live many happy years after diagnosis.
Kinds of Diabetes
Humans are subject to essentially three kinds of diabetes. By far the most common is Type 2, followed by Type 1 and gestational diabetes. Type 2 diabetes has typically been a disease of middle and old age (though it is being seen increasingly in young people), and has two causes: The beta cells don’t make enough insulin, or muscle cells resist insulin’s help and don’t take in enough glucose (or both). As a result, blood glucose levels climb. Type 1 diabetes usually occurs when the immune system attacks and destroys the beta cells, cutting off insulin production; the reason for this attack is thought to be a combination of genetic predisposition plus exposure to a trigger (research into possible triggers is ongoing). Glucose then stays in the blood and, again, levels skyrocket. Roughly half of people who have Type 1 diabetes develop it by age 20. Gestational diabetes starts during pregnancy and is probably caused by hormonal changes.
You may have heard that dogs generally get Type 1 diabetes, but the reality is more complicated. Though there are no universally accepted definitions of dog diabetes, the United Kingdom’s Royal Veterinary College identifies two forms: insulin-deficiency diabetes (IDD) and insulin-resistance diabetes (IRD). Neither matches any kind of human diabetes exactly.
In IDD, a dog loses beta cells and no longer makes enough insulin to keep glucose levels under control. Causes include genetic defects, inflammation of the pancreas and immune attack (as in human Type 1 diabetes). In IRD, something prevents the dog’s insulin from functioning properly. That “something” may be “diestrus,” pregnancy, an endocrine disease, or treatment with steroids or progesterone-like hormones. Diestrus, the most common cause of IRD, is the approximately two months of high levels of progesterone (a female hormone) between periods of estrus (heat). Hormonally, diestrus resembles pregnancy, making this form of IRD similar to human gestational diabetes.
Several factors raise a dog’s risk of developing diabetes. These include breed, age, gender, weight, diet, virus infections, an inflamed pancreas, chronic inflammation of the small bowel, Cushing’s disease (excess production of the hormone cortisol) and long-term use of progesterone-like drugs or steroid drugs.
•Breed. A study published in the Veterinary Journal in 2003 examined diabetes rates in thousands of American dogs and found that overall, mixed-breed dogs were more prone to diabetes than purebreds. Among purebreds, breeds varied greatly in their susceptibility.
•Age. Dogs most often develop diabetes during middle or old age.
•Gender. Female dogs and neutered male dogs are more likely than intact males to get diabetes.
•Weight. Obesity can make cells resistant to insulin, but it’s unclear whether it actually causes diabetes in dogs.
•Diet. A diet high in fat may contribute to pancreatitis (inflamed pancreas), a risk factor for diabetes.
Signs, Symptoms, Diagnosis
Diabetes can be a silent disease. Your veterinarian may discover your dog’s diabetes through routine bloodwork, but before that, you are likely to notice some of its symptoms: greater than normal hunger and/or thirst, weight loss, and frequent or copious urination (some dogs start having accidents in the house).