Diabetes and African Americans

Some researchers believe that African Americans inherited a "thrifty gene" from their African ancestors. Years ago, this gene enabled Africans, during "feast and famine" cycles, to use food energy more efficiently when food was scarce. Today, with fewer such cycles, the thrifty gene that developed for survival may instead make the person more susceptible to developing type 2 diabetes.

Today, diabetes mellitus is one of the most serious health challenges facing the United States. The following statistics illustrate the magnitude of this disease among African Americans.

• In 1998, of 35 million African Americans, about 1.5 million have been diagnosed with diabetes. This is almost 4 times the number known to have diabetes in 1968.

• About 730,000 African Americans have diabetes but do not know they have the disease. Identifying these undiagnosed cases and providing clinical care for their diabetes is a major challenge for the health care community.

• For every six white Americans who have diabetes, 10 African Americans have diabetes.

• Diabetes is particularly common among middle-aged and older adults and among African American women. Among African Americans age 50 years or older, 19 percent of men and 28 percent of women have diabetes.

• African Americans with diabetes are more likely to develop diabetes complications and experience greater disability from the complications than white Americans with diabetes.

• Death rates for people with diabetes are 27 percent higher for blacks compared with whites.

Diabetes mellitus is a group of diseases characterized by high levels of blood glucose. It results from defects in insulin secretion, 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 such occurrences.

Most African Americans (about 90 percent to 95 percent) with diabetes have type 2 diabetes. This type of diabetes usually develops in adults and is caused by the body's resistance to the action of insulin and to impaired insulin secretion. It can be treated with diet, exercise, diabetes pills, and injected insulin. A small number of African Americans (about five percent to 10 percent) have type 1 diabetes, which usually develops before age 20 and is always treated with insulin.

Diabetes can be diagnosed by three methods:

• A fasting plasma glucose test and a value of 126 milligrams/deciliter (mg/dL) or greater.

• A nonfasting plasma glucose value of 200 mg/dL or greater in people with symptoms of diabetes.

• 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 one of the above methods. The criteria used to diagnose diabetes were revised in 1997.

The prevalence for African American men and women is based on the most recent national study, the NHANES III survey conducted in 1988-94. The proportion of the African American population that has diabetes rises from less than one percent for those aged younger than 20 years to as high as 32 percent for women age 65-74 years. In every age group, prevalence is higher for women than men: overall, among those age 20 years or older, the rate is 11.8 percent for women and 8.5 percent for men. About one-third of total diabetes cases are undiagnosed among African Americans. This is similar to the proportion for other racial/ethnic groups in the United States.

National health surveys during the past 35 years show that the percentage of the African American population that has been diagnosed with diabetes is increasing dramatically. The surveys in 1976-80 and in 1988-94 measured fasting plasma glucose and thus allowed an assessment of the prevalence of undiagnosed diabetes as well as of previously diagnosed diabetes. In 1976-80, total diabetes prevalence in African Americans age 40-74 years was 8.9 percent; in 1988-94, total prevalence had increased to 18.2 percent--a doubling of the rate in just 12 years.

Prevalence in African Americans is much higher than in white Americans. Among those age 40-74 years in the 1988-94 survey, the rate was 11.2 percent for whites, but was 18.2 percent for blacks--diabetes prevalence in blacks is 1.6 times the prevalence in whites.

The frequency of diabetes in African American adults is influenced by the same risk factors that are associated with type 2 diabetes in other populations. Two categories of risk factors increase the chance of developing type 2 diabetes. The first is genetics. The second is medical and lifestyle risk factors, including impaired glucose tolerance, gestational diabetes, hyperinsulinemia and insulin resistance, obesity, and physical inactivity.

The common finding that "diabetes runs in families" indicates that there is a strong genetic component to type 1 and type 2 diabetes. Many scientists are now conducting research to determine the genes that cause diabetes. For type 1 diabetes, certain genes related to immunology have been implicated. For type 2 diabetes, there seem to be diabetes genes that determine insulin secretion and insulin resistance. Some researchers believe that African Americans inherited a "thrifty gene" from their African ancestors. Years ago, this gene enabled Africans, during "feast and famine" cycles, to use food energy more efficiently when food was scarce. Today, with fewer such cycles, the thrifty gene that developed for survival may instead make the person more susceptible to developing type 2 diabetes.

Impaired Glucose Tolerance (IGT)

In some people, their blood glucose level after a meal or after an oral glucose test rises higher than is considered normal but not high enough for them to be diagnosed with diabetes. These individuals are described as having impaired glucose tolerance (IGT). IGT may be an early stage of diabetes, and people with IGT are at higher risk of developing type 2 diabetes than people with normal glucose tolerance. Rates of IGT among adults age 40-74 years in the NHANES III survey were similar for black (13 percent) and white (15 percent) Americans.

About two to five percent of pregnant women develop mild abnormalities in glucose levels and insulin secretion and are considered to have gestational diabetes. Although these women's glucose and insulin levels often return to normal after pregnancy, as many as 50 percent may develop type 2 diabetes within 20 years of the pregnancy.

Higher-than-normal levels of fasting insulin, called hyperinsulinemia, are associated with an increased risk of developing type 2 diabetes. Hyperinsulinemia often predates diabetes by several years. Among people who did not have diabetes in the NHANES III survey, insulin levels were higher in African Americans than in whites, particularly African American women, indicating their greater predisposition for developing type 2 diabetes.


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