Age and sex-specific relationships between phthalate exposures and obesity in Chinese children at puberty

Abstract

Objective: To examine the age and sex-specific associations of urine levels of six mono-phthalates with body size and fat distribution in Chinese children at puberty.

Materials and methods: Four hundred and ninety-three school-aged children (247 boys, 246 girls) were recruited. Obesity related anthropometric indices were measured and body fat proportion (BF%) was calculated. Spot urine samples were collected and phthalate monoesters were detected by an API 2000 electrospray triple quadrupole mass spectrometer (ESI-MS/MS). Associations between phthalate exposure and overweight/obesity measures and their trends were examined by multiple linear regression and Logistic regression analyses, respectively.

Results: Di-2-ethylhexyl phthalate (DEHP) metabolites and monobutyl phthalate (MBP) were found to be the most detectable chemicals. In 8-10 years (yrs) group, concentrations of MEHP and MBP were significantly higher in girls than those in boys. However, concentrations of all phthalate monoesters, except for MEP and MEHP, in 11-13 yrs boys were significantly higher than those in girls. After adjusting for confounders including puberty onset, urinary concentrations of MBP and sum of low molecular-weight phthalate metabolites (∑LMP) were positively associated with boys' obesity in a concentration-effect manner, while concentrations of MEHP, MEHHP and sum of DEHP metabolites (∑MEHP) were negatively associated with girls' obesity. Associations between phthalate exposure levels and BMI z-score changes were age- and sex-specific in school-age children.

Conclusion: There are age and sex-specific concentration-effect associations between phthalate exposure and fat distribution in Chinese children. Urinary phthalate levels in 11-13 yrs boys were about 30 percent higher than those in girls, and ∑MEHP levels in younger boys (<10 yrs) were significantly higher than those in elder boys (>10 yrs). Associations were positive for MBP and ∑LMP with both BMI z-score and fat distribution in boys >10 years of age, and negative for ∑MEHP with fat distribution in girls <10 years of age.

Figure 1. Associations between exposure quartiles for log-transformed concentrations of MEHHP and ∑All monoesters and body fat distribution indices with significant continuous regression coefficients in 8-10yrs boys of China, corrected for puberty onset, socio-economic level, physical activity and dietary nutriment intake.

(Blue rhombus: regression coefficient; Error bar: 95% confidence interval; log-transformed indices including subscapular skinfold thickness, triceps skinfold thickness and BF ratio; BMI, BMI z-score, waist circumference, hip circumference, and BSA were normally distributed data)

Figure 2. Associations between exposure quartiles for log-transformed concentrations of MBP and ∑LMP and body fat distribution indices with significant continuous regression coefficients in 11-13yrs boys of China, corrected for puberty onset, socio-economic level, physical activity and dietary nutriment intake.

(Blue rhombus: regression coefficient; Error bar: 95% confidence interval; log-transformed indices including subscapular skinfold thickness, triceps skinfold thickness and BF ratio; BMI, BMI z-score, waist circumference, hip circumference, and BSA were normally distributed data)

Figure 3. BMI z-score in relation to urinary phthalate metabolite concentrations, by median (ppb) quartiles for ∑All in 8-10yrs boys (A), MBP and ∑LMP in 11-13yrs boys (B), and ∑MEHP in 8-10yrs girls (C).

Obesity and normal weight children were stratified by age- and gender-specific weight distribution based on the national survey in Chinese school children, normal weight children (<80th %) and obesity children (≥90th%), National Puberty Timing and Health Effects in Chinese Children (PTHEC) study, Shanghai 2010-2012.