Why is type 2 diabetes on the rise?

The Canadian Diabetes Association reports that nine million Canadians live with diabetes or prediabetes and 20 new cases are diagnosed every hour. For this first instalment in a series on diabetes and the work of U of T researchers, writer Jenny Hall sat down with Dr. Bernard Zinman, professor of medicine at U of T and senior investigator at the Samuel Lunenfeld Research Institute of Mount Sinai Hospital.

A world-leader in the study of both type 1 and type 2 diabetes, Zinman’s interests are in the long-term complications of diabetes, the evaluation of new therapies and diabetes in aboriginal populations.

Our series focuses on type 2 diabetes, but can we start by talking a little about the difference between type 1 and type 2?
Type 1 diabetes is an autoimmune disease that results in destruction of the beta cells of the pancreas. These are the cells that make insulin. In type 1, the body attacks its own beta cells. In type 2, you have insulin resistance, mostly as a result of obesity and a sedentary lifestyle. Since in some people the beta cells are unable to overcome this insulin resistance by producing more insulin, the blood sugar cannot be controlled. Type 2 diabetes results.

What causes insulin resistance?
Obesity is the most common cause. Obesity is an insulin-resistant state. But the majority of obese people do not develop diabetes.

So this means that insulin resistance does not always lead to diabetes.
Correct. We have an obesity epidemic. Obese people are insulin-resistant, but the majority of them make enough extra insulin to compensate—obese people have insulin levels at least three times higher than slim people. But there is a subset of obese people, who, when they become insulin-resistant, their beta cells also fail. Their beta cells cannot respond to the insulin resistance. That’s what type 2 diabetes is. When you look at the gene differences that predispose you to type 2 diabetes, they’re all beta cell genes. A certain genetic makeup predisposes you to diabetes when stressed by insulin resistance.

How big an issue is type 2 diabetes? We hear that it’s on the rise.
By 2030 there will be half a billion people with diabetes in the world. There’s no country or ethnic group that’s immune, but the biggest epidemic is going to be in India and China. Overnutrition—too much food—leads to an increased risk of diabetes, but its effect is different in different populations. For example, South Asians have an increased risk based on genetic predisposition. With excessive calories and a sedentary life style, they develop central or abdominal obesity, which is the most metabolically harmful type.

Another population that’s particularly susceptible is Canada’s aboriginal population. Historically, they were hunters and gatherers and extremely fit and very lean. More recently they have been exposed to calorie-dense, unhealthy diets, have high unemployment and very little physical activity and, not unexpectedly, obesity has resulted.

What are the consequences for an individual person? How much does having type 2 diabetes shorten your lifespan?
Type 2 diabetes is associated with devastating long term complications. These include visual impairment, kidney failure, erectile dysfunction, amputation, heart attack and stroke. These complications can significantly reduce life expectancy but with appropriate control of diabetes, blood pressure and cholesterol, these complications can be mostly avoided.

What are the symptoms?
It’s often a disease that has no symptoms. On average, people have diabetes for six to seven years without knowing it. It’s important to have annual check-ups, particularly if you’re at high risk—if you’re overweight, elderly, have a family history or are part of an ethnic group that’s at higher risk. A simple blood test can diagnose diabetes.

As diabetes progresses, you eventually develop symptoms: weight loss, excessive urination, blurred vision, vaginal infections in women, fatigue. These are the classic symptoms of diabetes.

How can people prevent it?
What’s driving the high rates of type 2 diabetes is the obesity epidemic—there’s no question about this. Nutrient excess, obesity and a sedentary life style are the principal causes of diabetes. There is no specific food type that causes diabetes, but refined sugars and fat are major sources of the nutrient excess. The best thing you can do to prevent diabetes is eat a healthy diet, remain lean and participate in regular exercise. This is particularly important if you have a family history. Studies have demonstrated that a seven per cent reduction in body weight and 30 minutes of exercise five days a week reduces the risk of type 2 diabetes by 58 per cent.

What about your own research?
We have several research programs examining new therapies for diabetes and strategies to prevent complications. More recently we are evaluating a new approach to treating diabetes. Generally speaking, people in the early stages of diabetes aren’t treated with insulin. But it turns out that if you treat people with insulin early in the course of type 2 diabetes, you can put their pancreas at rest. In this context we are doing a study with people who have had diabetes for less than eight years. We initiate a short course of insulin therapy, generally for less than four weeks. This puts their diabetes into remission because it rests the beta cells, allowing their pancreas to recover. But unfortunately, this remission doesn’t last. So we’re evaluating a new medication to see if we can sustain the remission achieved with a short period of insulin therapy. If a person has type 2 diabetes for less than eight years and wants to hear more about this study they can call our research coordinator at Mount Sinai Hospital at 416-586-8775.

This has been an abridged version of the interview with Dr. Zinman. To read more visit: http://www.research.utoronto.ca/behind_the_headlines/why-is-type-2-diabetes-on-the-rise/