Organophosphate Flame Retardants, Obesity, and Depressive Symptoms among 1019 Young Healthy Men

Organophosphate flame retardants (OPFRs) can increase fat accumulation and exert neurotoxic effects. In this study, we enrolled 1019 young men who provided 3,550 urine samples over a 3-month follow-up period. We measured nine OPFR metabolite concentrations in urine samples and assessed depressive symptoms using the Beck Depression Inventory questionnaire. In the fully adjusted linear regression models, a 2.7-fold increase in urinary diphenyl phosphate (DPHP) concentrations was associated with a 0.44 unit (95% confidence interval (CI): 0.06, 0.82) higher depressive symptom scores. When men were categorized as having any depressive symptoms (score: > 10 vs ≤ 10), Poisson regression models showed an increased risk of depression across DPHP tertiles (P _trend = 0.08). Further, we found stronger associations between urinary OPFR metabolite concentrations and depressive symptom scores among men with a higher waist circumference, waist-hip ratio, or waist-height ratio (P _interaction < 0.15). The machine learning algorithm identified three different patterns of obesity, and the strongest association between urinary DPHP concentrations and depressive symptom scores was observed among men with a waist-hip ratio of ≥ 0.89 and a body mass index of <24 kg/m². In summary, exposure to OPFRs may be associated with depressive symptoms among young men, especially in those with abdominal obesity.