Relationships between urinary phthalate metabolite concentrations and chronotypes of college students

Background Studies have found that endocrine disruptors phthalates are related to sleep disorder. College students are in late adolescence, and their chronotypes shift to the night type at its peak.

Objective This study examines the associations between phthalates exposure and chronotypes in college students.

Methods From October to November 2019, a questionnaire survey and urine sample collection was conducted among 1 152 college students from 2 universities in Anhui and Jiangxi provinces. Finally, 713 participants with complete questionnaire information and urine samples were enrolled in the study. The basic information was investigated with self-designed electronic questionnaires on healthrelated behaviors of college students. Chronotypes (morning type, night type, or intermediate type) were assessed by the Morning and Evening Questionnaire (MEQ). Concentrations of six phthalates metabolites in urine were determined by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). Chi-square test was used to examine the differences of chronotypes among college students with different demographic characteristics. A generalized linear model (GLM) was used to evaluate the sex-stratified relationships between phthalates metabolites and chronotypes. According to the tertiles, concentrations of phthalates metabolites were divided into low (< P_33.3), medium (P_33.3-P_66.7), and high (≥ P_66.7) level groups. Chronotypes were modelled as a categorical variable. Phthalates metabolites were included as a continuous variable or a categorical variable.

Results The positive rates of night type, intermediate type, and morning type of selected college students were 8.0%, 68.0%, and 24.0%, respectively. There were statistically significant differences in the distribution of chronotypes in different sex, academic major, residence, only-child, and physical activity groups (P< 0.05). The positive rates of urinary monomethyl phthalate (MMP), monoethyl phthalate (MEP), mono(2-ethyl-5-hydroxyhexyl)phthalate (MEHHP), monobutyl phthalate (MBP), mono(2-ethyl-5-oxohexyl)phthalate (MEOHP), and mono-2-ethylhexyl phthalate (MEHP) were 97.5%, 97.9%, 98.6%, 98.6%, 98.7%, and 80.5%, respectively, and the specific gravity standardized median concentrations were 16.02, 24.61, 15.33, 263.25, 12.19, and 2.94 μg·L^-1, respectively. After controlling confounding factors, MMP was negatively associated with chronotypes in female (OR=0.55; 95% CI: 0.33-0.89) by the GLM; MMP was negatively associated with chronotypes in female with high-level group (OR=0.51; 95% CI: 0.28-0.92), and the trend test result of MMP was statistically significant (P< 0.05). No association was found between selected six phthalates metabolites and chronotypes in male.

Conclusion The selected college students are widely exposed to multiple phthalates. MMP was associated with night type in female college students.