Bimodality of 2-h Plasma Glucose Distributions in Whites

Abstract

OBJECTIVE -Several studies have shown a bimodal curve in the distribution of glucose in populations with a high prevalence of type 2 diabetes, but bimodality has not been reported among whites of Northern European ancestry. It is not clear whether this difference reflects the lower prevalence of diabetes, obscuring a second mode, or implies a more fundamental difference between whites and nonwhites. We investigate this issue by studying glucose distributions in older white patients. RESEARCH DESIGN AND METHODS-A study of diabetes was conducted among older community-dwelling white residents of a suburban Southern California community between 1984 and 1987. Two-hour plasma glucose data were collected from 2,326 older white men and women aged 23-92. To investigate bimodality of glucose distributions, we fit unimodal and bimodal normal models to 2-h plasma glucose concentrations transformed by the Box-Cox family of transformations.RESULTS -We found that the bimodal normal mixture model fit the data significantly better than the unimodal skewed distribution model for both sexes and all age-groups except those Ն80 years. The cut points separating the two modes were generally within the 11.1-to 13.6-mmol/l range.CONCLUSIONS -The bimodality of glucose distributions among whites, combined with previous findings, indicates that this phenomenon may be universal. A smaller second mode in our study compared with other studies suggests that whites have diabetes susceptibility but may require more obesity to demonstrate it. With increasing obesity in the U.S., the predicted epidemic of diabetes may affect all ethnic groups including whites. Diabetes Care 28:1451-1456, 2005A bimodal distribution of plasma glucose concentrations in a population was first described in a 1971 study on Pima Indians, who have the highest prevalence of type 2 diabetes in the world (1). A bimodal curve showing two distinct distributions of plasma glucose concentrations, instead of a single skewed distribution, is compatible with a genetic condition (diabetes) manifest by hyperglycemia and a second population without diabetes (without hyperglycemia). Subsequently, bimodality was reported in other populations with a high prevalence of diabetes, including Nauruans from Micronesia (2), Samoans (3), Asian Indians who had migrated to South Africa (4), and Mexican Americans who were ϳ50% white (5). The diversity of populations with glucose bimodality suggests that this may be a universal phenomenon, readily detected in populations with a high prevalence of diabetes. To our knowledge, no studies have reported a bimodal glucose distribution among whites of Northern European ancestry, suggesting either genetic/environmental differences or a prevalence of diabetes too low to detect a second mode (6,7).We hypothesized that statistically significant bimodality might be detectable in older white patients because the prevalence of diabetes increases to nearly 20% in old age (8) and because most genetically susceptible people might be expected to develop diabetes if ...

Bimodal Distribution of Glucose Is Not Universally Useful for Diagnosing Diabetes

“…However, the estimated cut points were inconsistent between countries, especially for 2-h plasma glucose when participants with known diabetes were included. Comparing these results with those of earlier studies, we found that the overall cut point for FPG was somewhat lower (2,3,8,9), whereas the cut point for 2-h plasma glucose was well in line (1)(2)(3)5,8,10,11,13), except for the studies of South African Indians (9) and Western Samoans (12), which produced lower cut points for 2-h plasma glucose.…”

“…This exclusion potentially makes the two components less distinct and thereby decreases the probability of a meaningful cut point separating them. However, as acknowledged in previous studies (3,10,13), including patients with known diabetes in the analyses will induce a treatment bias for the following reasons. In accordance with existing treatment guidelines, patients with diabetes are treated with the aim of lowering their glucose to a near-normal range.…”

“…Here, bimodality was shown in 2-h plasma glucose values but with differing cut points for normal glycemia. Only one study has demonstrated bimodality in white Caucasians (13).…”

Can Yoga-Based Diabetes Management Studies Facilitate Integrative Medicine in India Current Status and Future Directions

“…It contributes the majority of increased cases of morbidity and mortality, poor quality of life along with the economic burden on the existing healthcare systems independently for management and preventive approaches. The highly susceptible populations which show differences in the diagnostic criteria for DM are Mexican American [38], Pacific Islanders [39], South African Indians [40], Egyptians [41], Malaysians [42], and Americans in the United States [43]. Asian Indian phenotypes (abnormal clinical and biochemical disturbances seen in Indians) include IR, greater abdominal adiposity (waist circumference, WC), low body mass index (BMI) and occurrence of T2DM onset at an earlier age compared with Caucasians [44,45].…”

Diagnosing Diabetes With Glucose Criteria: Worshipping a False God

“…If glucose concentrations are log-transformed to minimize the rightward skewness, a bimodal distribution has been noted (4–8). However, cutoff values defining the two distributions have ranged from 200–307 mg/dL, mostly depending on the ages of the population surveyed (3–8). …”