| Summary: | Abstract Background Folate is considered to be related to lipid metabolism. With the increasing numbers of folic acid fortification nations, the associations of dietary folate and serum folate with lipid profiles deserve more attention and are worth further study. Methods US adults aged ≥ 20 years from the National Health and Nutrition Examination Survey (NHANES) were evaluated. Participants taking folic acid supplements were excluded. The multivariate linear regression model and smooth curve fitting were applied to assess the associations. The segmented regression model was employed to examine the threshold effect of nonlinear relationships. Results Our cross-sectional study included 3706 participants in total. There was a negative relationship between serum folate (log transformed) and triglycerides (β = –0.223, 95% CI: –0.337, –0.110) and low-density lipoprotein cholesterol (LDL-C) (β = –0.152, 95% CI: –0.296, –0.007) and a positive relationship between serum folate (log transformed) and high-density lipoprotein cholesterol (HDL-C) (β = 0.090, 95% CI: 0.033,0.146). There was a negative association between dietary folate (log transformed) and total cholesterol (TC) (β = –0.299, 95% CI: –0.465, –0.134) and LDL-C (β = –0.266, 95% CI: –0.409, –0.123). A nonlinear relationship was found between dietary folate (log transformed) and HDL-C. Threshold effect analysis showed that the inflection point was 377.57 ug. Within the inflection point, the β-coefficient of HDL-C was 0.105 (95% CI: 0.018, 0.192); beyond the inflection point, there was no relationship (β = –0.067, 95% CI: –0.162, 0.028). Conclusions Optimal dietary folate and high serum folate were associated with favorable lipid profiles. Dietary folate, in the recommended 300–400 ug/d, had a beneficial effect on improving lipid profiles.
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