Diabetes in African Americans

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.

What is Diabetes?

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 5 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 1997.¹

Figure 1. - Prevalence of diagnosed and undiagnosed diabetes in African Americans, U.S., 1988-94.

Note: Diabetes includes both previously diagnosed diabetes and undiagnosed diabetes (fasting plasma glucose greater than 126 mg/dL).

How Many African Americans Have Diabetes?

Figure 1 shows the prevalence for African American men and women based on the most recent national study, the NHANES III survey conducted in 1988-94.² The proportion of the African American population that has diabetes rises from less than 1 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.²

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.³ 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.²

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.²

What Risk Factors Increase the Chance of Developing Type 2 Diabetes?

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.

• Genetic Risk Factors

  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.

• Medical Risk Factors

  • Impaired Glucose Tolerance (IGT)

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    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.²

  • Gestational Diabetes (GDM)

    About 2 to 5 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.

  • Hyperinsulinemia and Insulin Resistance

    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.⁴ Another study showed a higher rate of hyperinsulinemia in African American adolescents compared with white American adolescents.⁵

  • Obesity

    Overweight is a major risk factor for type 2 diabetes. The NHANES surveys found that overweight is increasing in the United States, both in adolescents and in adults. Figure 2 illustrates these data and also shows that African American adults have substantially higher rates of obesity than white Americans.^6,7

    In addition to the overall level of obesity, the location of the excess weight is also a risk factor for type 2 diabetes. Excess weight carried above the waist is a stronger risk factor than excess weight carried below the waist. African Americans have a greater tendency to develop upper-body obesity, which increases their risk of diabetes.

    Although African Americans have higher rates of obesity, researchers do not believe that obesity alone accounts for their higher prevalence of diabetes. Even when compared with white Americans with the same levels of obesity, age, and socioeconomic status, African Americans still have higher rates of diabetes. Other factors, yet to be understood, appear to be responsible.

  • Physical Activity

    Regular physical activity is a protective factor against type 2 diabetes and, conversely, lack of physical activity is a risk factor for developing diabetes. Researchers suspect that a lack of exercise is one factor contributing to the high rates of diabetes in African Americans. In the NHANES III survey, 50 percent of black men and 67 percent of black women reported that they participated in little or no leisure time physical activity.⁸

How Does Diabetes Affect African-American Young People?

African American children seem to have lower rates of type 1 diabetes than white American children. Researchers tend to agree that genetics probably makes type 1 diabetes less common among children with African ancestry compared with children of European ancestry.

How Does Diabetes Affect African American Women during Pregnancy?

Gestational diabetes, in which blood glucose values are elevated above normal during pregnancy, occurs in about 2 percent to 5 percent of all pregnant women. Perinatal problems such as macrosomia (large body size) and neonatal hypoglycemia (low blood sugar) are higher in these pregnancies. The women generally return to normal glucose values after childbirth. However, once a woman has had gestational diabetes, she has an increased risk of developing gestational diabetes in future pregnancies. In addition, experts estimate that about half of women with gestational diabetes develop type 2 diabetes within 20 years of the pregnancy.

Several studies have shown that the occurrence of gestational diabetes in African American women may be 50 percent to 80 percent more frequent than in white women.

How Do Diabetes Complications Affect African Americans?

Compared with white Americans, African Americans experience higher rates of diabetes complications such as eye disease, kidney failure, and amputations. They also experience greater disability from these complications. Some factors that influence the frequency of these complications, such as high blood glucose levels, abnormal blood lipids, high blood pressure, and cigarette smoking, can be influenced by proper diabetes management.

• Eye Disease

  Diabetic retinopathy is a deterioration of the blood vessels in the eye that is caused by high blood glucose. It can lead to impaired vision and, ultimately, to blindness. The frequency of diabetic retinopathy is 40 percent to 50 percent higher in African Americans than in white Americans, according to NHANES III data.⁹ Retinopathy may also occur more frequently in black Americans than in whites because of their higher rate of hypertension. Although blindness caused by diabetic retinopathy is believed to be more frequent in blacks than in whites, there are no valid studies that compare rates of blindness between the two groups.

• Kidney Failure

  African Americans with diabetes experience kidney failure, also called end-stage renal disease (ESRD), about four times more often than diabetic white Americans.¹⁰ In 1995, there were 27,258 new cases of ESRD attributed to diabetes in black Americans.¹¹ Diabetes is the leading cause of kidney failure and accounted for 43 percent of the new cases of ESRD among black Americans during 1992-1996. Hypertension, the second leading cause of ESRD, accounted for 42 percent of cases. In spite of their high rates of ESRD, African Americans have better survival rates after they develop kidney failure than white Americans.¹⁰

• Amputations

  Based on the U.S. hospital discharge survey, there were about 13,000 amputations among black diabetic individuals in 1994, which involved 155,000 days in the hospital.¹² African Americans with diabetes are much more likely to undergo a lower-extremity amputation than white or Hispanic Americans with diabetes. The hospitalization rate of amputations for blacks was 9.3 per 1,000 patients in 1994, compared with 5.8 per 1,000 white diabetic patients. However, the average length of hospital stay was lower for African Americans (12.1 days) than for white Americans (16.5 days).

Figure 3. - Mortality rates in black and white diabetic men and women in a sample of the U.S. population, 1971-1993.

Age in 1971-75

Does Diabetes Cause Excess Deaths in African Americans?

Diabetes was an uncommon cause of death among African Americans at the turn of the century. By 1994, however, death certificates listed diabetes as the seventh leading cause of death for African Americans. For those age 45 years or older, it was the fifth leading cause of death.¹²

Death rates (mortality) for people with diabetes are higher for blacks than for whites. Figure 3 shows death rates for whites and blacks with diabetes in a national survey of people first studied in 1971-1975 whose mortality was confirmed through 1992-1993.¹³ In every age group and for both men and women, death rates for blacks with diabetes were higher than for whites with diabetes. The overall mortality rate was 20 percent higher for black men and 40 percent higher for black women, compared with their white counterparts.

References

NIDDK