Type 2 diabetes develops most often in middle-aged and older people who are also overweight or obese. The disease, once rare in youth, is becoming more common in overweight and obese children and adolescents. Scientists think genetic susceptibility and environmental factors are the most likely triggers of type 2 diabetes.
Genetic Susceptibility
Genes play a significant part in susceptibility to type 2 diabetes. Having certain genes or combinations of genes may increase or decrease a person’s risk for developing the disease. The role of genes is suggested by the high rate of type 2 diabetes in families and identical twins and wide variations in diabetes prevalence by ethnicity. Type 2 diabetes occurs more frequently in African Americans, Alaska Natives, American Indians, Hispanics/Latinos, and some Asian Americans, Native Hawaiians, and Pacific Islander Americans than it does in non-Hispanic whites.Recent studies have combined genetic data from large numbers of people, accelerating the pace of gene discovery. Though scientists have now identified many gene variants that increase susceptibility to type 2 diabetes, the majority have yet to be discovered. The known genes appear to affect insulin production rather than insulin resistance. Researchers are working to identify additional gene variants and to learn how they interact with one another and with environmental factors to cause diabetes
Studies have shown that variants of the TCF7L2 gene increase susceptibility to type 2 diabetes. For people who inherit two copies of the variants, the risk of developing type 2 diabetes is about 80 percent higher than for those who do not carry the gene variant.1 However, even in those with the variant, diet and physical activity leading to weight loss help delay diabetes, according to the Diabetes Prevention Program (DPP), a major clinical trial involving people at high risk.
Genes can also increase the risk of diabetes by increasing a person’s tendency to become overweight or obese. One theory, known as the “thrifty gene” hypothesis, suggests certain genes increase the efficiency of metabolism to extract energy from food and store the energy for later use. This survival trait was advantageous for populations whose food supplies were scarcer unpredictable and could help keep people alive during famine. In modern times, however, when high-calorie foods are plentiful, such a trait can promote obesity and type 2 diabetes.
Obesity and Physical Inactivity
Physical inactivity and obesity are strongly associated with the development of type 2 diabetes. People who are genetically susceptible to type 2 diabetes are more vulnerable when these risk factors are present.An imbalance between caloric intake and physical activity can lead to obesity, which causes insulin resistance and is common in people with type 2 diabetes. Central obesity, in which a person has excess abdominal fat, is a major risk factor not only for insulin resistance and type 2 diabetes but also for heart and blood vessel disease, also called cardiovascular disease (CVD). This excess “belly fat” produces hormones and other substances that can cause harmful, chronic effects in the body such as damage to blood vessels.
The DPP and other studies show that millions of people can lower their risk for type 2 diabetes by making lifestyle changes and losing weight. The DPP proved that people with prediabetes—at high risk of developing type 2 diabetes—could sharply lower their risk by losing weight through regular physical activity and a diet low in fat and calories. In 2009, a follow-up study of DPP participants—the Diabetes Prevention Program Outcomes Study (DPPOS)—showed that the benefits of weight loss lasted for at least 10 years after the original study began.2
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