Total folate, natural folate and synthetic folic acid intake associations with adult depressive symptoms.

Background and objectives In the United States, synthetic folic acid has become an important source of folate in the era of mandatory folic acid fortification. This study aimed to evaluate the associations between total folate, natural folate and synthetic folic acid intakes and depressive symptoms among US adults. Methods and study design Cross-sectional data was collected from the National Health and Nutrition Examination Survey (NHANES) 2007-2016. Dietary data were obtained through two 24-h dietary recall interviews. Depressive symptoms were detected by PHQ-9 (Patient Health Questionnaire-9), participants whose depression scores over 10 points were diagnosed as depressive symptoms. Weighted logistic regressions were used to analyze the associations between different forms of folate and depressive symptoms. Results Among 19244 participants included in this study, 9.2% of them met the definition of depressive symptoms. In fully adjusted models, total folate intake and natural folate intake were inversely associated with depressive symptoms respectively, while synthetic folic acid was not. The multivariate-adjusted odds ratios (ORs) with 95% confidence intervals (CIs) of depressive symptoms were 0.69 (0.54-0.89), 0.51 (0.39-0.68) for the highest versus lowest quartile of total folate and natural folate intake, respectively. We also found two L-shaped dose-response curves among total folate intake, natural folate intake with depressive symptoms, respectively. Conclusions Total folate intake, natural folate intake may be inversely associated with depressive symptoms among US adults, while the association was not significant between synthetic folic acid and depressive symptoms.