Even Normal and Low-Weight Minorities at Higher Diabetes Risk

Even at normal or below-normal body weight, certain racial and ethnic minorities were significantly more likely to have diabetes than whites, according to a large observational study.

Among normal-weight individuals, the prevalence of diabetes in Hawaiians and Pacific Islanders was more than three times higher than among whites (18% vs 5%; P<0.001), reported Yeyi Zhu, PhD, of the Kaiser Permanente Division of Research in Oakland, California, and colleagues.

The study, published online in Diabetes Care, included 4.9 million Americans of diverse backgrounds, and found that diabetes prevalence was also significantly higher among normal-weight blacks (13.5%), Hispanics (13%), Asians (10%), and American Indians/Alaskan Natives (9.6%) (P<0.001 for all). The trend was similar but somewhat less pronounced for pre-diabetes.

The researchers said that surprisingly, significant proportions of underweight individuals also had diabetes, and this trend was also more pronounced in ethnic and racial minorities. Among underweight whites, the prevalence was 3.5%, compared with 9.9% for blacks, 8.8% for Hispanics, 7.3% for Asians, and about 10% for Hawaiians and Pacific Islanders (P<0.001).

"We observed a positive linear trend in age-standardized prevalence of diabetes across BMI [body-mass index] categories among all racial/ethnic groups," Zhu and colleagues wrote. "However, racial/ethnic minorities reached a given prevalence at a much lower BMI than whites ... suggesting the role of factors other than obesity in the disproportionate burden of diabetes and prediabetes among racial/ethnic minorities and highlighting the need for tailored screening and prevention strategies."

Said study co-author Assiamira Ferrara, MD, PhD, also of the Kaiser Permanente Division of Research in Oakland, in a statement: "This study suggests that along with screening patients who are overweight and obese, minorities should probably be screened even if they have a normal BMI, particularly as they get older."

The team speculated that physiological differences among the races might explain the results: "Notably, compared with other racial/ethnic groups, Asians at a given BMI have a higher percentage of body fat and visceral fat, which in turn has been linked to insulin resistance and increased risk of diabetes. Further, Asians may experience innate susceptibility to impaired insulin secretion early in the development of diabetes."

Large Minority Samples

The study is one of the largest to examine relationships between diabetes and BMI across racial and ethnic groups, the researchers said. It analyzed electronic medical records from the Patient Outcomes Research to Advance Learning (PORTAL) network. This network included data on more than 12 million patients from all regions of Kaiser Permanente as well as HealthPartners in Minnesota and Denver Health. Notably, the researchers said, the network included large enough samples of minority groups to draw reliable conclusions, including more than 620,000 Asians, 67,000 Hawaiian/Pacific Islanders, and 26,000 American Indians/Alaskan Natives.

The study included health plan members ages 18 and older with height and weight measurements and at least 12 months of continuous membership from January 2012 through December 2013. Of the 4.9 million participants, 50% were white, 22% Hispanic, 13% Asian, 9.5% black, 1.4% Hawaiian or Pacific Islander, and 0.5% American Indian/Alaskan Native. Approximately 4% were multiracial or of unknown ethnicity, and slightly more than half (55.7%) were women.

Diabetes and pre-diabetes were determined by International Classification of Disease version 9 (ICD-9) codes, fasting or random plasma glucose measurements, or dispensation of anti-hyperglycemic medication. BMIs were categorized according to the World Health Organization's recommended racial/ethnic specific cutoffs. Socioeconomic factors such as income and education were estimated using geospatial entity object codes (geocodes) that linked addresses to census data.

The researchers used Poisson regression models to estimate relative risks for diabetes in association with BMI categories by race/ethnicity, adjusting for socioeconomic factors. When comparing normal-weight individuals with those who were most obese (class 4), the team found the highest risk in whites (RR 7.64, 95% CI 7.50-7.79), followed by:

• Asians (RR 6.26, 95% CI 5.83-6.72)

• American Indians/Alaskan Natives (RR 4.85, 95% CI 4.24-5.55)

• Hispanics (RR 4.53, 95% CI 4.41-4.67)

• Hawaiians/Pacific Islanders (RR 3.19, 95% CI 2.95-3.45)

• Blacks (RR 3.16, 95% CI 3.05-3.27)

These results again suggest that physiological mechanisms may differ and that factors other than obesity may play more important roles in diabetes risk among racial/ethnic minorities, Zhu and colleagues said.

Study limitations, the researchers said, included that they did not have direct measures of adiposity or visceral fat, which may be more strongly associated with insulin resistance and diabetes risk. "We also lacked data on lifestyle factors such as smoking, diet, and physical activity," the team continued. "Future studies examining the role of these potential intermediate factors is warranted to further explain the racial/ethnic disparities in diabetes or prediabetes across BMI levels."

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