Diabetes is caused by genetics and lifestyle factors. If left untreated, diabetes will damage vital organs and may lead to blindness, heart disease, kidney failure, gastrointestinal problems, and debilitating nerve pain. Type 1 diabetes is an autoimmune disease, where the insulin-producing cells in the pancreas have been destroyed. Type 2 diabetes is usually associated with sufficient or excess insulin but an inability of the body to use it.

According to the Centers for Disease Control and Prevention (CDC), type 1 diabetes accounts for about 5 percent of diabetes cases, while the majority (about 95 percent) of cases represents type 2 diabetes. Both type 1 and type 2 diabetes are in part caused by hereditary factors. The non-genetic causes or triggers of type 1 diabetes are not well established, whereas the lifestyle causes of type 2 diabetes are well defined.

Obesity/Overweight

Excess weight is a major risk factor for the development of type 2 diabetes. The more fatty tissue you have, the greater your risk is of becoming insulin resistant. Insulin resistance leads to type 2 diabetes. Insulin is a hormone that helps the cells in your body take up glucose, which cells then use to generate energy. In insulin resistance, even high concentrations of insulin may fail to trigger glucose to enter cells.

You are most likely to develop type 2 diabetes if most of your fat is located in your abdominal region rather than around your hips and thighs. Not all obese individuals develop diabetes -- other risk factors also play a role.
Poor Diet

A high-fat diet is a risk factor for type 2 diabetes. But any high-calorie diet, whether the calories come from fat, carbohydrates, or sugar, will increase your weight and risk of diabetes. It is not necessary to eat a strict "diabetic" diet; any healthy diet rich in whole grains, vegetables, and fruit in low to moderate portions, may prevent or reverse the development of diabetes.
Inactivity

Lack of activity or exercise contributes to type 2 diabetes. Physical activity lowers blood sugar. Aerobic activities such as walking, biking, or swimming are helpful. Strength training will also lower your blood sugar. Try exercising for at least 30 minutes per day.
Genes

A family history of type 2 diabetes predisposes you to developing diabetes, but because obesity also runs in families, it is difficult to distinguish the genetic component from lifestyle and diet factors. However, studies on identical twins (people with the same basic DNA), demonstrate that genetics does play its own role independent of diet and exercise.

Ethnicity

According to the National Institute of Diabetes and Digestive and Kidney Diseases, Asian Americans have an 18 percent greater risk than non-Hispanic whites of developing type 2 diabetes. People of Hispanic descent have a 66 percent greater risk, and non-Hispanic blacks have a 77 percent greater risk. It is not clear whether genes or lifestyle or both play a role in these differences.
Age

The risk for type 2 diabetes increases with age, especially after age 45. Weight gain, inactivity, and muscle loss are probably contributing factors. Type 2 diabetes used to be called "adult-onset" diabetes, but recently, type 2 diabetes among children and young adults has increased dramatically.