Diabetes and Hispanic Americans

Hispanic Americans with diabetes have a higher incidence of diabetes complications, such as eye and kidney disease, than non-Hispanic whites. However, they may have lower rates of heart disease.

Diabetes in Hispanic Americans is a serious health challenge because of the increased prevalence of diabetes in this population, the greater number of risk factors for diabetes in Hispanics, the greater incidence of several diabetes complications, and the growing number of people of Hispanic ethnicity in the United States.

The following statistics illustrate the magnitude of diabetes among Hispanic Americans:

• In 1998, of the 30 million Hispanic Americans, about 1.2 million have been diagnosed with diabetes.

• About 675,000 Hispanic Americans have diabetes but do not know they have it. Identifying these undiagnosed cases and providing medical care for their diabetes is a major challenge for the health care community.

• Diabetes is particularly common among middle-aged and older Hispanic Americans. For those age 50 or older, about 25 to 30 percent have either diagnosed or undiagnosed diabetes.

• Diabetes is two to three times more common in Mexican American and Puerto Rican adults than in non-Hispanic whites. The prevalence of diabetes in Cuban Americans is lower, but still higher than that of non-Hispanic whites.

• As in all populations, having risk factors for diabetes increases the chance that a Hispanic American will develop diabetes. Risk factors seem to be more common among Hispanics than non-Hispanic whites. These factors include a family history of diabetes, gestational diabetes, impaired glucose tolerance, hyperinsulinemia and insulin resistance, obesity, and physical inactivity.

• Higher rates of the diabetes complications nephropathy (kidney disease), retinopathy (eye disease), and peripheral vascular disease have been documented in studies of Mexican Americans, whereas lower rates of myocardial infarctions (heart attacks) have been found.

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 Hispanic Americans with diabetes (about 90 to 95 percent) 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 Hispanic Americans (about five 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.

Five population studies conducted in the past 20 years provide the majority of information that exists about the incidence and progression of diabetes among Hispanic Americans. The five studies are briefly described below:

• The Starr County Study (Texas) conducted in 1981 assessed the prevalence of severe hyperglycemia (high blood glucose levels) in almost 2,500 people age 15 or older.

• The San Antonio Heart Study (Texas), begun in 1979 and still being conducted, assessed diabetes in more than 3,000 Mexican Americans and almost 2,000 non-Hispanic whites between the ages of 25 and 64.

• The San Luis Valley Diabetes Study (Colorado), a continuing study that began in 1984, estimated the prevalence of diabetes in Hispanics and non-Hispanic whites in two counties in southern Colorado.

• The Hispanic Health and Nutrition Examination Survey (HHANES), 1982-84, investigated the prevalence of diabetes in national samples of the three major Hispanic subgroups--Mexican Americans in the southwestern United States, Puerto Ricans in the New York City area, and Cuban Americans in south Florida. Approximately 6,600 people participated.

• The Third National Health and Nutrition Examination Survey (NHANES III), 1988-94, determined the prevalence and characteristics of people with diabetes in national samples of African Americans, Mexican Americans, and whites. Approximately 18,000 adults participated.

Hispanic Americans are the second-largest and fastest growing minority group in the United States. In 1998, there were 30 million Hispanics in the United States, representing 11 percent of the population. By the year 2050, it is estimated that Hispanics will number 97 million and constitute 25 percent of the U.S. population.

Mexican Americans represent the largest Hispanic American subgroup, with 64.3 percent of the Hispanic population. Central and South Americans represent the second-largest Hispanic American subgroup, with 13.4 percent of the Hispanic population. The majority of Hispanic Americans live in the south-central and southwestern United States.

Based on the most recent national study, the NHANES III survey conducted in 1988-9, the proportion of the Mexican American population that has diabetes (defined by medical history or fasting plasma glucose of 126 mg/dL or greater) rises from less than one percent for those younger than 20 to as high as 33 percent for women age 60 to 74. In almost every age group, prevalence is higher among women than men. About one-third of total diabetes among Hispanic Americans is undiagnosed. This is similar to the proportion for other racial/ethnic groups in the United States.

Prevalence in Hispanic Americans is much higher than in Americans without Hispanic ancestry. Among those age 40 to 74 in the 1988-94 survey, the rate was 11.2 percent for non-Hispanic whites, but 20.3 percent for Mexican Americans--in other words, the prevalence of diabetes in Mexican Americans is 1.8 times higher than in non-Hispanic whites.

The frequency of diabetes in Hispanic 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 comprises medical and lifestyle risk factors, including impaired glucose tolerance, gestational diabetes, hyperinsulinemia and insulin resistance, obesity, and physical inactivity.

A family history of diabetes increases the chance that people will develop diabetes. The San Antonio Heart Study showed that the prevalence of diabetes among Mexican Americans who have first-degree relatives (e.g., parents) with diabetes was twice as great as for those with no family history of diabetes.

Having American Indian or African genes (populations with a high prevalence of diabetes) is also thought to be a factor that causes the higher rates of diabetes in Hispanics. Hispanics, like all populations, inherit their susceptibility to diabetes from their ancestors. Hispanics have three groups of ancestors--Spaniards, American Indians, and Africans. Both American Indians and Africans have high rates of diabetes.

Although Cuban Americans have both American Indian and African ancestry, neither of these genetic roots contributes more than 20 percent to the current Cuban American gene pool. This may partly explain why Cuban Americans have a higher prevalence of type 2 diabetes than non-Hispanic white Americans, although not as high as the other Hispanic groups.

In some people, the blood glucose level after a meal or after an oral glucose test rises more than is considered normal, but not enough to be diagnosed as diabetes. These individuals are described as having impaired glucose tolerance. This may be an early stage of diabetes, and people with impaired glucose tolerance are at higher risk of developing type 2 diabetes than people with normal glucose tolerance. Rates of impaired glucose tolerance among adults age 40 to 74 in the NHANES III survey were higher for Mexican Americans (19 percent) than for non-Hispanic white Americans (15 percent).

About two to five percent of pregnant women in the United States develop mild abnormalities in glucose levels, insulin secretion and insulin resistance 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. Mexican American women may be at particularly high risk for developing type 2 diabetes. One study of 666 women with gestational diabetes in southern California found that each year an average of 12 percent developed type 2 diabetes after pregnancy.

Hyperinsulinemia (higher than normal levels of fasting insulin) and insulin resistance (an inability to use the body's own insulin to properly control blood glucose) are both hallmarks of an increased risk for 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 Mexican Americans than in non-Hispanic whites, indicating their greater predisposition for developing type 2 diabetes. Several other studies have also shown a higher rate of hyperinsulinemia in Hispanics than in non-Hispanics.

Obesity is a major risk factor for type 2 diabetes. Many racial/ethnic groups in the United States have high rates of obesity, and surveys show that obesity is increasing. Hispanics are more likely than non-Hispanic whites to be overweight. Mexican American adults, particularly women, have substantially higher rates of obesity than non-Hispanic white Americans, but rates that are similar to those of African Americans.

The degree to which obesity is a risk factor for diabetes depends not just on overall weight, but also 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. Mexican Americans with upper body obesity have an increased risk of type 2 diabetes.

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 Hispanic Americans. In the NHANES III survey, 65 percent of Mexican American men and 74 percent of Mexican American women reported that they participated in little or no leisure-time physical activity.

HHANES data showed that fewer men with high levels of work-related physical activity had diabetes. The San Antonio Heart Study also found that decreased leisure-time physical activity was related to a higher incidence of diabetes.

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