Interestingly, in the past several decades, the number of people with diabetes has doubled. Some of that increase is due to an aging population, as people with type 1 diabetes now live longer. But most of the dramatic rise in diabetes is due to an increase in a second form of the disease—type 2 diabetes. Its increase is primarily attributed to the increased prevalence of obesity and decreased physical activity of our population—and not just in adults, incidence in those under 20 years of age is increasing as well. Today, 9 of 10 people with diabetes have type 2 diabetes.

Although type 1 diabetes is typically diagnosed in children and young adults, type 2 is most frequently seen in adults. Unlike type 1, in which insulin-producing pancreatic cells are destroyed and there is little or no insulin made, type 2 diabetes occurs when cells are less sensitive to the effects of insulin, even if the pancreas is able to produce normal amounts. Obesity is by far the most significant risk factor for the disease: 80% to 90% of people with type 2 diabetes are obese. In addition to having excess body fat, physical inactivity is another factor that significantly affects the risk of developing diabetes. However, genetics and lifestyle factors also potently affect an individual’s risk of disease. If one identical twin has diabetes, the other twin will also have the disease 75% of the time. In addition, the risk of diabetes is higher among African-Americans, Hispanics and Latinos, American-Indians, Asian-Americans, and Pacific Islanders than among white people.

Type 2 diabetes begins with the development of insulin resistance. Most often this occurs because excess adipose tissue produces hormone-like substances that circulate throughout the body and interfere with the signal that insulin sends into cells to stimulate glucose uptake. As a result, muscle and fat cells do not respond properly to insulin and poorly take up glucose from the blood. The body then needs higher levels of insulin to help glucose enter cells. The cells of the pancreas produce more of the hormone to try to meet the demand. In some insulin-resistant individuals the pancreas can no longer keep up with the increased demand for insulin, and blood glucose concentrations increase. Insulin resistance also blocks insulin’s ability to adequately suppress liver glucose production, contributing further to the increase in blood glucose levels. (INFOGRAPHIC 5.2)

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Question 5.2

Without intervention and lifestyle changes, many people who have insulin resistance go on to develop type 2 diabetes. However, they may first develop prediabetes, a condition in which blood glucose levels are moderately elevated above levels that are considered normal or desirable. For example, after fasting for eight hours, the blood glucose levels of someone with prediabetes would measure 100 mg to 125 mg per 100 ml blood, which is elevated but still less than the fasting level of at least 126 mg per ml that is required for a diagnosis of diabetes. After ingesting glucose as part of an oral glucose tolerance test (OGTT), the same person would have elevated blood glucose levels in the 140 mg to 199 mg per 100 ml range—just under the 200 mg/100 ml diagnostic level for diabetes. (INFOGRAPHIC 5.3) According to the American Diabetes Association, more than 33% of American adults older than 20 have prediabetes and fewer than 10% have been told they have it. Prediabetes not only increases the risk of type 2 diabetes, but also heart disease, stroke, and other conditions associated with elevated blood glucose levels. However, as we will see, there are lifestyle strategies, including weight control, physical activity, and dietary modifications that can normalize blood glucose levels and prevent or delay onset or impact of type 2 diabetes.

Question 5.3

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Because all forms of diabetes decrease the body’s ability to remove glucose from the blood, each can cause blood glucose concentrations to increase to dangerous levels, leading to similar symptoms—feeling constantly thirsty (as the kidneys excrete the extra glucose through urine), blurred vision (as extra glucose enters the eye), and weight loss (due to low insulin levels and muscle cells relying on burning fat for energy). Over time, high levels of blood glucose can damage cells and organs, creating long-term problems in the heart, blood vessels, kidneys, eyes, and nerves. The excess glucose causes blood vessels to thicken and lose some of their elasticity, making these people more prone to heart attacks and stroke. Even today, with all the vast improvements in treatment, diabetes is the number one cause of adult blindness, and is responsible for more than 60% of lower limb amputations that don’t result from trauma. (INFOGRAPHIC 5.4)

Question 5.4

Pregnant women can develop a form of diabetes known as gestational diabetes. Approximately 18% of expectant mothers will experience high blood glucose levels for the first time during pregnancy, and this can affect their pregnancy—increasing the rate of complications or causing the baby to grow too large. Obese women are at higher risk, so are often screened early in their pregnancies. Extra exercise can reduce the risk, while high-fiber and a low-glycemic index diet can help keep blood glucose at healthy levels. For many women, gestational diabetes goes away once they give birth, but they will remain at a higher risk of developing type 2 diabetes later in life. (INFOGRAPHIC 5.5)

Question 5.5