Why is type 2 diabetes on the rise?

By Jenny Hall
André Menegatti, sxc.hu

The Canadian Diabetes Association reports that nine million Canadians live with diabetes or prediabetes and that 20 new cases are diagnosed every hour. “We are currently in the middle of a global epidemic of type 2 diabetes,” says Dr. Bernard Zinman, professor of medicine at U of T and senior investigator at the Samuel Lunenfeld Research Institute of Mount Sinai Hospital “Canada is similarly affected and this tsunami of diabetes will have a devastating impact on the patients affected, their families and the health care system.”

Today we launch a four-week series on by talking to Dr. Zinman. 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. He serves as director of the Leadership Sinai Centre for Diabetes, a unique, multi-disciplinary outpatient unit that is one of the largest diabetes clinical research units in Ontario.

This week, Dr. Zinman gives us an orientation to type 2 diabetes: what happens in the body of a diabetic?  How can we treat and prevent it? How serious is the problem? In subsequent weeks we’ll talk to Professor Thomas Wolver about relationship between diabetes and diet, to Professor Greg Wells about how exercise can be used to treat diabetes and to Professor Daniel Drucker about new frontiers in diabetes drugs.

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 . 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.

We used to hear type 1 called “juvenile diabetes” and type 2 called “adult onset.” Why the name change?

We have recently observed that young adults and children are getting type 2. In addition it is also possible for older people to get type 1 diabetes. As a result, the classification and terminology of diabetes has changed to “type 1″ and “type 2″ as opposed to “juvenile” and “adult onset.” In addition to being caused by environmental factors, both type 1 and type 2 have a strong genetic risk.

So in type 2 you have insulin resistance. Can you explain what insulin is and what it means to become resistant to it?

Insulin is the key regulator of metabolism. It balances blood glucose and regulates protein and lipid (fatty acid) metabolism.

If you are resistant to insulin, it’s not able to do its job. In order for everything to work properly in your body, you’ll need to produce much more insulin than is usually required. Insulin is a signalling hormone. It interacts with its receptor on various tissues to control important metabolic pathways. When you’re insulin resistant, you need more insulin in order to get the appropriate response. So people who are insulin resistant have to produce a lot more insulin. Providing your pancreas can respond in this way, you will not develop type 2 diabetes. However, if your pancreas cannot respond to this increased need for insulin, blood glucose increases and 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.

So it’s not about sugar, as we often believe. Whatever makes you overweight is what causes diabetes.

Exactly. It’s very easy to gain weight in our modern environment of high-calorie, supersized fast foods.

You mentioned that diabetes is linked to abdominal fat in particular. 

Yes. Not all fat is created equal. The worst place for fat to be is in your organs. Some people store fat under the skin—called subcutaneous fat—and they’re OK. Others fill those fat depots up, and then the fat goes into the abdomen. It’s called visceral fat. It’s in your liver, pancreas and bowel. Fat in these sites is metabolically active and contributes to insulin resistance and reduced insulin production.

How to you treat or manage type 2 diabetes?

I look at the diabetes epidemic as requiring three strategies. The first is prevention. We know we can prevent type 2 diabetes with exercise and weight loss.

The second strategy targets people who already have diabetes, You need to focus on cardiometabolic control. This means we need to make sure your blood pressure, cholesterol and blood sugar are in control. We do this with medication and with lifestyle interventions.

Finally, for those who have complications of diabetes, we need to do more. We treat eye complications with laser therapy. If you have kidney complications, there are good drugs for that. If you have nerve damage, you need good foot care so you don’t develop an ulcer and need an amputation. If you have heart disease, you might need surgery or cardiac medication.

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 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.

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