Gender and racial/ethnic differences in the associations of urinary phthalate metabolites with markers of diabetes risk: National Health and Nutrition Examination Survey 2001-2008

Abstract

Background: Phthalates are ubiquitous endocrine disrupting chemicals associated with diabetes. Although women and minorities are more likely to be exposed to phthalates, no prior studies have examined phthalate exposure and markers of diabetes risk evaluating effect modification by gender and race/ethnicity.

Methods: We analyzed CDC data for 8 urinary phthalate metabolites from 3,083 non-diabetic, non-pregnant participants aged 12- < 80 years in the National Health and Nutrition Examination Survey (NHANES) 2001-2008. We used median regression to assess the associations between urinary phthalate metabolites and fasting blood glucose (FBG), fasting insulin and Homeostatic Model Assessment of insulin resistance (HOMA-IR), controlling for urinary creatinine as well as several sociodemographic and behavioral factors. Stratified analyses were conducted to compare the gender- and race/ethnicity-specific patterns for the associations.

Results: Urinary levels of several phthalate metabolites, including MBzP, MnBP, MiBP, MCPP and ∑DEHP showed significant positive associations with FBG, fasting insulin and HOMA-IR. No clear difference was noted between men and women. Mexican-Americans and non-Hispanic blacks had stronger dose-response relationships for MnBP, MiBP, MCPP and ∑DEHP compared to non-Hispanic whites. For example, the highest quartile of MiBP relative to its lowest quartile showed a median FBG increase of 5.82 mg/dL (95% CI: 3.77, 7.87) in Mexican-Americans, 3.63 mg/dL (95% CI: 1.23, 6.03) in blacks and 1.79 mg/dL (95% CI: -0.29, 3.87) in whites.

Conclusions: The findings suggest that certain populations may be more vulnerable to phthalates with respect to disturbances in glucose homeostasis. Whether endocrine disrupting chemicals contribute to gender and racial/ethnic differences in diabetes risk will be an important area for further study.

Figure 1

Change in markers of diabetes risk across quartiles of markers of diabetes risk in men and women. One example is selected for each pattern. (a) example of similar strength of association: ∑DEHP and HOMA-IR, most associations show similar gender patterns, (b) example of stronger association in women: MBzP and fasting insulin, (c) example of stronger association in men: ∑DEHP and FBG. Adjusted for age, race, urinary creatinine, fasting time, total caloric intake, triglyceride, education, smoking status and poverty for all phthalate metabolites.

Figure 2

Change in markers of diabetes risk across quartiles of urinary phthalate metabolites in racial/ethnic subgroups. One example is selected for each diabetes biomarker, and similar racial/ethnic patterns were seen for other urinary phthalate metabolites, particularly MnBP, MiBP, MCPP and ∑DEHP. (a) example of FBG: MiBP and FBG, (b) example of fasting insulin: ∑DEHP and fasting insulin, (c) example of HOMA-IR: ∑DEHP and HOMA-IR. Adjusted for age, sex, urinary creatinine, fasting time, total caloric intake, triglyceride, education, smoking status and poverty for all phthalate metabolites.