Diabetes in African Americans
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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.
- 2.8 million African Americans have diabetes.1
- On average, African Americans are twice as likely to have diabetes
as white Americans of similar age.1
- Approximately 13 percent of all African Americans have diabetes.1
- 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 African
Americans compared with whites.
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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 with 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 1997.2
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How many African Americans have diabetes?
Figure 1 shows the prevalence for African American
men and women based on the NHANES III survey conducted in 1988-94.3
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. 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.3
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.4
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 ages 40 to 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.3
Prevalence in African Americans is much higher than in white Americans.
Among those ages 40 to 74 years in the 1988-94 survey, the rate was 11.2
percent for whites, but was 18.2 percent for African Americans.
Figure 1.--Prevalence
of diagnosed and undiagnosed diabetes in African Americans,
U.S., 1988-94.
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Note: Diabetes
includes both previously diagnosed diabetes and undiagnosed diabetes
(fasting plasma glucose greater than 126 mg/dL). |
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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
Pre-diabetes (Impaired Glucose Tolerance and Impaired Fasting Glucose)
In some people, blood glucose levels are higher than normal but not high
enough for them to be diagnosed with diabetes. These individuals are described
as having pre-diabetes, also called impaired glucose tolerance (IGT) or impaired
fasting glucose (IFG). People with pre-diabetes are at higher risk of developing
type 2 diabetes than people with normal glucose tolerance. Rates of IGT
among adults ages 40 to 74 years in the NHANES III survey were similar for
African Americans (13 percent) and white (15 percent) Americans.3
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.5
Another study showed a higher rate of hyperinsulinemia in African American
adolescents compared with white American adolescents.6
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.7,8
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.
Figure 2.--Time
trends in the percentage of adolescents and adults in the U.S.
who are overweight, U.S., 1988-94.
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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 African American men and 67 percent of African American women
reported that they participated in little or no leisure time physical activity.9
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How does diabetes affect African American children?
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.
However, recent reports indicate an increasing prevalance of type 2 diabetes
in children, especially in those with African American, American Indian,
or Hispanic family background.10
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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.
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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.11
Retinopathy may also occur more frequently in African Americans than in
whites because of their higher rate of hypertension. Although blindness
caused by diabetic retinopathy is believed to be more frequent in African
Americans 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.12
In 1995, there were 27,258 new cases of ESRD attributed to diabetes in African
Americans.13 Diabetes
is the leading cause of kidney failure and accounted for 43 percent of the
new cases of ESRD among African 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.12
Amputations
Based on the U.S. hospital discharge survey, there were about 13,000 amputations
among African American diabetic individuals in 1994, which involved 155,000
days in the hospital.14
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 African Americans 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).
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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.14
Death rates (mortality) for people with diabetes are higher for African
Americans than for whites. Figure 3 shows death rates for whites and African
Americans with diabetes in a national survey of people first studied in
1971-1975 whose mortality was confirmed through 1992-1993.15
The overall mortality rate was 20 percent higher for African American
men and 40 percent higher for African American women, compared with their
white counterparts.
Figure 3.--Mortality
rates in African American and white diabetic men and women in
a sample of the U.S. population, 1971-1993.
Age in 1971-75
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Hope Through Research
Within many African American communities around
the country, NIDDK supports centers that provide nutrition counseling, exercise,
and screening for diabetes complications. These centers are called Diabetes
Research and Training Centers.
Prevention
In 1996, NIDDK launched its Diabetes Prevention Program (DPP). The goal
of this research effort was to learn how to prevent or delay type 2 diabetes
in people with impaired glucose tolerance (IGT), a strong risk factor
for type 2 diabetes.
The findings of the DPP, which were released in August 2001, showed that
people at high risk for type 2 diabetes could sharply lower their chances
of developing the disease through diet and exercise. In addition, treatment
with the oral diabetes drug metformin also reduced diabetes risk, though
less dramatically. These results were so striking that the DPP's external
data monitoring board advised ending the trial early.16
Participants randomly assigned to intensive lifestyle intervention reduced
their risk of getting type 2 diabetes by 58 percent. On average, this
group maintained their physical activity at 30 minutes per day, usually
with walking or other moderate intensity exercise, and lost 5 to 7 percent
of their body weight. Participants randomized to treatment with metformin
reduced their risk of getting type 2 diabetes by 31 percent.
Of the 3,234 participants enrolled in the DPP, 45 percent were from minority
groups that suffer disproportionately from type 2 diabetes: African Americans,
Hispanic Americans, Asian Americans and Pacific Islanders, and American
Indians. The trial also recruited other groups known to be at higher risk
for type 2 diabetes, including individuals age 60 and older, women with
a history of gestational diabetes, and people with a first-degree relative
with type 2 diabetes. Participants ranged from age 25 to 85, with an average
age of 51.
Lifestyle intervention successfully reduced the risk of getting type
2 diabetes for both men and women, and across all the ethnic groups. It
reduced the development of diabetes in people age 60 and older by 71 percent.
Metformin was also effective in men and women and in all the ethnic groups,
but was relatively ineffective in the older volunteers and in those who
were less overweight.
Researchers will continue to analyze the data to determine whether the
interventions reduced cardiovascular disease and atherosclerosis, major
causes of death in people with type 2 diabetes. The DPP is the first major
trial to show that diet and exercise can effectively delay diabetes in
a diverse American population of overweight people with IGT.
National Diabetes Education Program
NIDDK and the Centers for Disease Control and Prevention are jointly sponsoring
the National Diabetes Education Program (NDEP). Its goal is to reduce the
death and disability associated with diabetes and its complications. The
NDEP conducts ongoing diabetes awareness and education activities for people
with diabetes and their families. Special efforts are being made to address
the needs of certain ethnic groups that are hardest hit by diabetes, including
African Americans, Hispanic Americans, Asian Americans, Pacific Islanders,
and American Indians. Through these efforts, the NDEP hopes to improve
the treatment and outcomes for people with diabetes, promote early diagnosis,
and, ultimately, prevent the onset of diabetes.
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Points to Remember
- 2.8 million African Americans have diabetes.
- On average, African Americans are twice as likely to have diabetes
as white Americans of similar age.
- The highest incidence of diabetes in African Americans occurs between
65 and 74 years of age. Twenty-five percent of these individuals have
diabetes.
- Obesity is a major medical risk factor for diabetes in African Americans,
especially for women. Some diabetes may be prevented with weight control
through healthy eating and regular exercise.
- African Americans have higher incidence of and greater disability
from diabetes complications such as kidney failure, visual impairment,
and amputations.
- People at high risk for type 2 diabetes, including African Americans,
can prevent or delay diabetes with modest weight loss and regular exercise.
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References
1. National Diabetes Information Clearinghouse. National diabetes statistics. NIH publication 02-3892. 2002. Fact sheet. Available at: www.niddk.nih.gov/health/diabetes/pubs/dmstats/dmstats.htm.
Accessed April 4, 2002.
2. American Diabetes Association. Report of the Expert
Committee on the Diagnosis and Classification of Diabetes Mellitus. Diabetes
Care. 1997;20:1183-1197.
3. Harris MI, Flegal KM, Cowie CC, et al. Prevalence
of diabetes, impaired fasting glucose, and impaired glucose tolerance
in U.S. adults: the Third National Health and Nutrition Examination Survey,
1988-94. Diabetes Care. 1998;21:518-524.
4. Tull ES, Roseman JM. Diabetes in African Americans.
Chapter 31 in Diabetes in America, 2nd ed. (NIH Publication No.
95-1468), pp. 613-630. Bethesda, MD: National Institute of Diabetes and
Digestive and Kidney Diseases, National Institutes of Health; 1995. Available
at: http://diabetes.niddk.nih.gov/dm/pubs/america/index.htm.
5. Harris MI. Unpublished data from the Third National
Health and Nutrition Examination Survey, 1988-94.
6. Jiang X, Srinivasan SR, Radhakrishnamurthy B, Dalferes
ER, Berenson GS. Racial (African American-white) differences in insulin
secretion and clearance in adolescents: the Bogalusa heart study. Pediatrics. 1996;97:357-360.
7. Kuzmarski RJ, Flegal KM, Campbell SM, Johnson CL.
Increasing prevalence of overweight among US adults: the National Health
and Nutrition Examination Surveys, 1960 to 1991. Journal of the American Medical Association. 1994;272:205-211.
8. Troiano RP, Flegal KM, Kuczmarski RJ, Campbell SM,
Johnson CL. Overweight prevalence and trends for children and adolescents.
Archives of Pediatrics and Adolescent Medicine. 1995;149:1085-1091.
9. Crespo CJ, Keteyian SJ, Heath GW, Sempos CT. Leisure-time
physical activity among US adults. Archives of Internal Medicine. 1996;156:93-98.
10. Ludwig DS, Ebbeling CB. Type 2 diabetes mellitus
in children. Journal of the American Medical Association. 2001;286:1427-1430.
11. Harris MI, Klein R, Cowie CC, Rowland M, Byrd-Holt
DD. Is the risk of diabetic retinopathy greater in non-Hispanic African
Americans and Mexican Americans than in non-Hispanic whites with type
2 diabetes: a US population study. Diabetes Care. 1998;21:1230-1235.
12. Cowie CC, Port FK, Wolfe RA, Savage PJ, Moll PP,
Hawthorne VM. Disparities in incidence of diabetic end-stage renal disease
by race and type of diabetes. New England Journal of Medicine. 1989;321:1074-1079.
13. U.S. Renal Data System. USRDS 1997 Annual Data
Report. Bethesda, MD: National Institute of Diabetes and Digestive
and Kidney Diseases, National Institutes of Health; 1997.
14. Geiss LS (ed.). Diabetes Surveillance,
1997. Atlanta: Centers for Disease Control and Prevention; 1997.
15. Gu K, Cowie CC, Harris MI. Mortality in adults
with and without diabetes in a national cohort of the US population, 1971-93.
Diabetes Care. 1998;21:1138-1145.
16. Diabetes Prevention Program Research Group. Reduction
in the incidence of type 2 diabetes with lifestyle intervention or metformin.
New England Journal of Medicine. 2002;346:393-403.
Statistics in this fact sheet were derived from NIDDK's fact sheet National
Diabetes Statistics.
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For More Information
National Diabetes Education Program
1 Diabetes Way
Bethesda, MD 20892-3600
Phone: 1-800-438-5383 or (301) 654-3327
Fax: (301) 907-8906
Internet: http://ndep.nih.gov
Weight-control Information Network
1 Win Way
Bethesda, MD 20892-3665
Phone: 1-800-WIN-8098 or (301) 951-1120
Fax: (301) 951-1107
Email: win@info.niddk.nih.gov
American Diabetes Association
National Service Center
1701 North Beauregard Street
Alexandria, VA 22311
Phone: (800) 232-3472
Fax: (703) 549-6995
Internet: www.diabetes.org
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National Diabetes Information Clearinghouse
1 Information Way
Bethesda, MD 20892-3560
Email: ndic@info.niddk.nih.gov
The National Diabetes Information Clearinghouse (NDIC) is a service of
the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).
The NIDDK is part of the National Institutes of Health under the U.S. Department
of Health and Human Services. Established in 1978, the clearinghouse provides
information about diabetes to people with diabetes and to their families,
health care professionals, and the public. NDIC answers inquiries, develops
and distributes publications, and works closely with professional and
patient organizations and Government agencies to coordinate resources
about diabetes.
Publications produced by the clearinghouse are carefully reviewed by both NIDDK scientists and outside experts.
This e-text is not copyrighted. The clearinghouse encourages users of
this e-pub to duplicate and distribute as many copies as desired.
NIH Publication No. 02-3266
May 2002
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