DIABETES

Non-insulin dependent diabetes mellitus (NIDDM) is a metabolic disorder characterized by abnormal glucose metabolism. NIDDM, or adult onset diabetes, has a different pathogenesis than insulin-dependent diabetes mellitus (IDDM), or juvenile onset diabetes . Persons with NIDDM have a relative, rather than absolute, deficiency in insulin production, and therefore are not prone to ketoacidosis. It is estimated that 90% of all diabetics have the non-insulin dependent type. Patients with all forms of diabete s mellitus are at risk for the late complications of the disease, including retinopathy, nephropathy and neuropathy. Persons with diabetes are also at greater risk for atherosclerotic large vessel disease than non-diabetics, and therefore have a higher i ncidence of myocardial infarction, congestive heart failure and stroke.

Since the terms Mexican, Mexican-American, and Hispanic are often used interchangeably, it is useful to review the prevalence of diabetes in national samples of the different Hispanic subpopulations of the U.S. Harris (1991) has analyzed the prevalence o f diabetes in the HHANES (Hispanic Health and Nutrition Survey) sample. The HHANES included a 2-hour standard oral glucose tolerance test which permitted the identification of both undiagnosed and diagnosed diabetes. The Hispanic populations represented in HHANES were Mexican-Americans from the southwestern U.S., Puerto Ricans in the New York City area, and Cuban Americans in Dade County, Florida. Age-standardized rates of total diabetes prevalence (diagnosed and undiagnosed) in the three Hispanic subp opulations compared to whites and Blacks examined in NHANES II (the 1976-80 National Health and Nutrition Examination Survey) are reported in Table 8.

Table 8. Age-standardized rates of diabetes and impaired glucose tolerance among Hispanics, whites, blacks aged 20-74 years in the U.S. population.

	Diabetes		Impaired glucose tolerance
	Age-standardized rate (%)	Rate relative to whites	Age-standardized rate (%)	Rate relative to whites
White	6.2	1.0	10.3	1.0
Cuban	9.3	1.5	10.8	1.0
Black	10.2	1.6	12.8	1.2
Mexican	13.0	2.1	13.8	1.3
Puerto Rican	13.4	2.2	12.5	1.2

*Sum of diagnosed and undiagnosed diabetes.

Source: Harris MI. Epidemiological Correlates of NIDDM in Hispanics, Whites, and Blacks in the U.S. population. Diabetes Care. 1991;14(Suppl 3):639-648.

Assignment:

Review the age-standardized rates of diabetes, and the rate ratios relative to whites, shown in Table 8 and answer the following questions.

1) Do all Hispanic subgroups have the same prevalence of diabetes?
2) Please list all of the factors you can think of that might account for the differences in the frequency of diabetes in the five U.S. racial/ethnic represented in Table 8.

Prevalence of diabetes (most of which is NIDDM) increases with age. Another strong risk factor is obesity. Harris examined the relationship between relative body weight (expressed as percent desirable weight) and prevalence of diabetes in Hispanics, whi tes and blacks (Figure 1).

Assignment:

Examine Figure 1 and answer the following questions.
1) What is the approximate prevalence of diabetes among Mexican Americans at 120-139% desirable body weight and at 140% ideal body weight?
2) What is the approximate prevalence of diabetes among whites at 120-139% and at >140% of desirable body weight?
3) Based on the curves presented in Figure 1, do you believe that differences in the prevalence of obesity between Blacks, Whites and Hispanics account for the differences in prevalence of diabetes?

It has been recognized for a number of years that persons of Mexican origin have a higher prevalence of NIDDM compared to the general U.S. population. The reasons for this higher incidence have not yet been clearly identified. One possible explanatio n is the Native American genetic admixture that characterizes many Mexicans and Mexican-Americans (Gardner et al., 1984). This hypothesis was motivated by the very high rates of NIDDM (up to 50% in adults) seen in certain Native American tribes from the southwestern U.S., most notably the Pima Indians.

Although a genetic basis for the high prevalence of NIDDM in Mexican-Americans is likely, there has been little progress in identifying candidate genes. However, two population-based studies have demonstrated that normoglycemic Mexican-Americans have hig her insulin levels than non-Hispanic whites (Haffner et al., 1986; Boyko et al., 1991). The higher insulin levels reflect resistance to insulin action in peripheral tissues, and are predictive of eventual NIDDM development. Lifestyle changes that reduc e insulin resistance, including weight loss and increased physical activity, should be recommended to persons at high risk for NIDDM, including Mexican-Americans and other Hispanic subgroups