Diabetes mellitus is one of the most serious health challenges facing American Indians and Alaska Natives in the United States today. The disease is very common in many tribes, and morbidity and mortality from diabetes can be severe.

This population includes all people who derive their origins from any of the original peoples of North America and who continue to maintain cultural identification through tribal affiliations or community recognition. Great diversity in culture, language, location, lifestyles, and genetic heritage exists among American Indians and Alaska Natives. More than 500 Native American tribal organizations, with many differences in language and culture, exist in the United States.

Diabetes mellitus is a group of diseases characterized by high blood levels of glucose. It results from defects in insulin secretion, in insulin action, or both. Diabetes can be associated with serious complications and premature death, but people with diabetes can take measures to reduce the likelihood of disability and death.

Most American Indians and Alaska Natives with diabetes have type 2 diabetes, which usually develops in adults but can develop in children or adolescents. Type 2 diabetes is caused by the body's resistance to the action of insulin and by impaired insulin secretion. It can be managed with healthy eating, physical activity, oral diabetes medications, and/or injected insulin. Until recently, type 2 diabetes was rarely diagnosed in children and adolescents. However, type 2 diabetes is now common in American Indian children age 10 and older. A small number of American Indians (about 2 to 4 percent) have type 1 diabetes, which usually develops before age 20 and is managed with insulin, healthy eating, and physical activity.

Diabetes can be diagnosed by three methods:

• A casual (random) plasma glucose value of 200 milligrams per deciliter (mg/dL) or greater in people with symptoms of diabetes.
• A fasting plasma glucose test with a value of 126 mg/dL or greater.
• An abnormal oral glucose tolerance test with a 2-hour glucose value of 200 mg/dL or greater.

Each test must be confirmed, on another day, by any of the above methods.

How Many American Indians and Alaska Natives Have Diabetes?

Type 2 Diabetes

About 15 percent of American Indians and Alaska Natives who receive care from the Indian Health Service have been diagnosed with diabetes, a total of 105,000 people. On average, American Indians and Alaska Natives are 2.6 times as likely to have diagnosed diabetes as non-Hispanic whites of a similar age. The available data probably underestimate the true prevalence of diabetes in this population. For example, 40 to 70 percent of American Indian adults age 45 to 74 were found to have diabetes in a recent screening study in three geographic areas. Data from the Navajo Health and Nutrition Survey, published in 1997, showed that 22.9 percent of Navajo adults age 20 and older had diabetes. Fourteen percent had a history of diabetes, but another 7 percent were found to have undiagnosed diabetes during the survey.

Type 2 diabetes is becoming increasingly common in youth. Researchers studying 5,274 Pima Indian children from 1967 to 1996 found that the prevalence of type 2 diabetes in girls ages 10 to 14 increased from 0.72 percent in the period 1967 to 1976 to 2.88 percent in the period 1987 to 1996. Reports include an increasing incidence in First Nation populations in Canada.

In 1998, about 70,000 of the 2.3 million self-identified American Indians/Alaska Natives who receive care from the IHS had diabetes. Diabetes is particularly common among middle-age and older American Indians and Alaska Natives. In Pima Indians, the most widely studied American Indian group, the prevalence of type 2 diabetes was approximately 50 percent in individuals ages 30 to 64.

The prevalence of type 2 diabetes in Alaska Natives varies by subgroup:

• Eskimo groups (Inupiaq Eskimos in the northern and northwestern coastal areas and Yup'ik Eskimos in the southwestern coastal regions and St. Lawrence Island) had a prevalence of 12.1 per 1,000 in 1993.
• Indian groups (Athabascan in the interior region; Tlingit, Haida, and Tsimshian in the coastal areas) had a prevalence of 24.3 per 1,000 in 1993.
• Aleut groups (residents of the Aleutian Islands, the Pribilof Islands, the western tip of the Alaska Peninsula, the Kodiak area, and the southcentral coastal areas) had a prevalence of 32.6 per 1,000 in 1993.

Type 1 Diabetes

Type 1 diabetes is relatively rare in American Indians and Alaska Natives. Most cases of type 1 diabetes are seen in people who have both American Indian and Caucasian heritage.

What Risk Factors Increase the Chance That American Indians and Alaska Natives Will Develop Type 2 Diabetes?

Two categories of risk factors increase the chance of type 2 diabetes. The first is genetics. The second is medical and lifestyle risk factors, including obesity, diet, and physical inactivity. Individuals with impaired glucose tolerance, impaired fasting glucose, or insulin resistance are at higher risk of progressing to diabetes.

Genetic Risk Factors

Genetic background is a determining factor in the prevalence of type 2 diabetes. In both the Choctaw Indians and the Pima Indians, the more full-blooded individuals were found to have the highest prevalence of type 2 diabetes, as compared with those of more mixed heritage. In Pima Indians, diabetes rates were found to be highest in children whose parents developed diabetes at an early age.

Although the specific genes responsible for the inheritance of type 2 diabetes have not been located, NIDDK scientists studying the Pima Indians have identified a gene called FABP2 that may play a role in insulin resistance. More recent studies have shown that a variant in the PPPIR3 gene that is more common in Pimas than Caucasians is associated with type 2 diabetes and insulin resistance.

Medical and Lifestyle Risk Factors

Obesity
Obesity is a major risk factor for type 2 diabetes among all races and ethnic groups. Increasing rates of obesity have been measured in many American Indian and Alaska Native communities. In Pima Indians, 95 percent of those with diabetes are overweight.

The study of obesity and energy metabolism in Pima Indians has not identified exact causes but has revealed that Pima Indian families share the trait of low metabolic rate. This trait is considered predictive of weight gain and development of type 2 diabetes. A "thrifty gene" is also thought to cause a genetic predisposition to obesity, although this gene has not been identified. The thrifty gene theory, first proposed in 1962, suggests that populations of indigenous people who experienced alternating periods of feast and famine gradually adapted by developing a way to store fat more efficiently during periods of plenty to better survive famines.

The degree to which obesity is a risk factor for diabetes depends greatly on the location of the excess weight. Central or upper-body obesity is a stronger risk factor for type 2 diabetes than excess weight carried below the waist. In young Pima Indians, waist-to-hip ratio, a measure of central obesity, was more strongly associated with diabetes than body mass index, a measure of overall obesity.

Diet and Physical Inactivity
Both diet and physical activity have changed for many members of American Indian and Alaska Native groups over the past several decades. Diets are higher in fat and calories than traditional diets; physical activity has decreased. Changes in diet and physical activity are associated with the increased prevalence of type 2 diabetes. For example, Pima Indians living in Mexico who consumed a more traditional diet (less animal fat and more complex carbohydrates) had a lower prevalence of type 2 diabetes than Pima Indians living in Arizona. Pima Indians in Mexico also expended more calories through activity.

Pre-diabetes (Impaired Glucose Tolerance and Impaired Fasting Glucose)
Recent recommendations describe two categories of the physiological state between normal blood glucose and the diabetic range of blood glucose. Individuals are described as having impaired glucose tolerance (a 2-hour glucose value of between 140 and 199 mg/dL during the oral glucose tolerance test) or impaired fasting glucose (a fasting plasma glucose value between 110 and 125 mg/dL).

American Indians with impaired glucose tolerance have a higher incidence of diabetes than those whose glucose tolerance test results are in the normal range.

Hyperinsulinemia and Insulin Resistance
Hyperinsulinemia (higher than normal levels of fasting insulin) and insulin resistance (the inability of the body to use its own insulin to properly control blood glucose) are both associated with an increased risk of developing type 2 diabetes. Hyperinsulinemia often predates diabetes by several years. Studies of Pima Indians have shown that both increased insulin secretion and insulin resistance occur in conjunction with impaired glucose tolerance.

Points to Remember

• About 15 percent of American Indians and Alaska Natives who receive care from the Indian Health Service have diabetes, mostly type 2 diabetes. Rates vary markedly among tribes.
• On average, American Indians and Alaska Natives are 2.6 times as likely to have diabetes as non-Hispanic whites of a similar age.
• Type 1 diabetes in American Indian and Alaska Native youth is relatively rare; however, recent reports highlight an increasing incidence of type 2 diabetes in children and adolescents.
• American Indians and Alaska Natives have genetic, medical, and lifestyle risk factors for type 2 diabetes.
• American Indians and Alaska Natives with diabetes have a high incidence of diabetes complications such as eye and kidney disease, cardiovascular disease, and lower extremity amputations.
• Cardiovascular disease was the leading cause of death in American Indians, and diabetes is a high contributing risk factor for cardiovascular disease

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