All Asian American subgroups showed higher prevalence of type 2 diabetes in comparison to NHWs and considerable heterogeneity existed among the individual Asian American subgroups in our study, especially after adjustment for subgroup differences in age and BMI. Among Asian Americans, the Asian Indian and Filipino subgroups had the highest prevalence of type 2 diabetes, regardless of age- and age-and-BMI adjustment. Treatment rates for type 2 diabetes were also 5-8% higher for Asian Americans as a group, and there was significant variation in treatment rates among the individual racial/ethnic subgroups.
Our results corroborate some of the findings from previous studies that have investigated type 2 diabetes prevalence in Asian American subgroups from large statewide (CHIS)[20
] or national datasets (NHIS).[9
] In their 2007 CHIS analysis of five Asian American racial/ethnic subgroups, Choi and colleagues found that Filipinos had the highest age-adjusted prevalence of type 2 diabetes, followed by Japanese, Vietnamese, Koreans, and Chinese, compared to NHWs.[20
] Asian Indians were not included in the study. Analyses of NHIS also demonstrate trends toward higher prevalence of diabetes in Asian Indians and Filipinos as compared to NHWs,[9
] and significantly higher prevalence of diabetes in the Asian Indian subgroup alone.[10
] These studies rely on telephone based self-report surveys, which may be inaccurate due to recall bias, social desirability bias, and respondents’ lack of knowledge.[28
] Some respondents may be misclassified when assessing the prevalence of type 2 diabetes, and there may be racial/ethnic differences in these misclassification rates due to decreased health literacy or disease knowledge in some subgroups.[29
] A strength of this clinical data is that it offers analysis of type 2 diabetes prevalence with data gathered from EHRs rather than self-report and it includes large sample sizes of all six major Asian American racial/ethnic subgroups.
In this cohort of prevalent type 2 diabetes, treatment with oral anti-diabetic medication varied across racial/ethnic subgroups from 59.7-82.0%. Some Asian American subgroups (Asian Indian, Filipino) had higher treatment rates than others. Across every Asian American subgroup, no difference was observed in treatment rates between women and men. It is reassuring that along with the observed higher rates of type 2 diabetes in Asian Americans, treatment rates are also high in this population. This may reflect higher medication prescription rates by physicians in this area enriched in Asian American patients, or a greater propensity for Asian American patients to take oral anti-diabetic medication for type 2 diabetes. However, it should be noted that this was not observed across all Asian American subgroups, and that Japanese patients had lower treatment rates in this cohort. Future studies should examine physician and patient factors in treatment patterns across disparate Asian American subgroups.
In our study, type 2 diabetes was defined in part by the use of oral anti-diabetic medication. We excluded patients with insulin treatment alone in order to minimize misclassification with type 1 diabetes. A 2004 evaluation of the National Health and Nutrition Examination Survey (NHANES) III showed that 16.4% of people with type 2 diabetes used insulin alone for treatment. Other treatment regimens include diet alone (20.2%), oral anti-diabetics alone without insulin (52.5%) and oral anti-diabetics and insulin together (11.0%).[21
] Most type 2 diabetics are treated with an oral anti-diabetic medication either with or without insulin. Assuming comparable usage to that found in NHANES[21
] (which included Black/African Americans, Hispanic/Latinos, and NHWs), we likely underestimate treatment rates of type 2 diabetes by excluding patients who used insulin alone in our definition of treatment. We also excluded treatment of type 2 diabetes with exenatide injection (Byetta). Byetta was FDA approved as primary monotherapy on October 30, 2009,[30
] however, it is doubtful that many patients in this cohort would have been treated with Byetta during the study period (January 1, 2007 – December 31, 2009).
It is unknown whether there are racial/ethnic differences between Asian Americans and NHWs in type 2 diabetes treatment regimens. For instance, if Asian Americans with type 2 diabetes are less likely to be treated with insulin alone, and NHWs with type 2 diabetes are more likely to be treated with insulin alone, then overall treatment rates may not actually be different. Therefore, our results should be interpreted with some caution. However, these observed differences in oral anti-diabetic medication treatment rates are noteworthy and should be explored further.
Relying on EHR for prevalence estimates may limit the external validity of the data, because EHR data are restricted to those individuals who choose to visit a clinic. Therefore, our results may only be generalizable to the clinical population. The sample size for women in our study is slightly higher than that of men in almost all Asian American racial/ethnic subgroups and in NHWs. The data suggest that in Asian American subgroups, women have much lower prevalence of type 2 diabetes as compared to men. It is possible that this finding results from higher use of healthcare services by women than by men.[31
] The prevalence of type 2 diabetes in men may be artificially inflated because men visit a clinic (and are then entered into the EHR) only after they have fully developed the disease. Increased odds of diabetes in men (OR 1.49) were also observed in the CHIS analysis of Asian Americans by Choi and colleagues.[20
] NHIS did not include Asian American subgroups by sex due to small sample size[9
] and there are no sex differences in diabetes prevalence observed in national data for NHWs.[32
In addition, the trends among different Asian American subgroups in this cohort may reflect specific cultural norms regarding rates of utilization of healthcare services. For example, Chinese have been shown to have a cultural reluctance to seek healthcare from individuals or organizations outside of their communities because of language barrier, transportation needs, and lack of trust in Western doctors.[33
] Cultural attitudes could lead to under- or over-estimation of the actual prevalence of type 2 diabetes in individual racial/ethnic subgroups. Further studies should investigate the clinically relevant norms and cultural practices specific to Asian American subgroups and health-seeking behaviors, in order to determine how they may play a role in diagnosis, prevalence, and treatment of diabetes.
Data from this clinical population cannot offer absolute national or statewide diabetes prevalence estimates because it is limited to one specific Northern California region and sub-population, but it is useful for relative racial/ethnic subgroup comparisons. Confounders, such as socioeconomic status, are attenuated in this population because all patients in the cohort are insured and of similar socioeconomic status from a specific region of the country. Thus, the age- and age-and-BMI adjusted odds ratios provide robust internal comparability (patients from a single organization in one geographic region, diminishing variation due to geography or practice), high quality of clinical measures, and a large patient population. These data can reveal relative type 2 diabetes prevalence estimates as well as the need to disaggregate Asian American subgroups in future studies.
In summary, our findings suggest that all Asian American racial/ethnic subgroups have a higher prevalence of type 2 diabetes when compared to NHWs. Asian Indian and Filipino subgroups in particular, have a higher prevalence of type 2 diabetes compared to other Asian American subgroups, even after adjustment for BMI. Our study also provides some evidence that treatment rates with oral anti-diabetic medications differ by racial/ethnic subgroup. These findings strengthen the argument for the importance of disaggregating data by Asian American racial/ethnic subgroups in future studies. Culturally sensitive lifestyle changes, including promotion of physical exercise and diet modification in a relevant context (e.g., recommendations on how to modify traditional recipes and portion sizes), have been shown to significantly decrease the progression of type 2 diabetes in Asian Indians[34
] and Filipinos.[35
] These findings suggest that the increased prevalence of type 2 diabetes found in Asian Indians and Filipinos can be partially mitigated by weight loss through lifestyle modifications. Further research should continue investigating these clinically important differences in type 2 diabetes and its risk factors among Asian American racial/ethnic subgroups.