The role played by serum folate in the progression of nonalcoholic fatty liver disease (NAFLD) remains controversial. The purpose of this study was to investigate the association of serum folate with NAFLD and advanced liver fibrosis (AHF). We conducted a cross-sectional study with 5417 participants using 2011–2018 NHANES data. Multiple logistic regression analysis and propensity score matching analysis were used to investigate the association of serum folate with NAFLD and AHF. In the completely adjusted model, participants in the high serum folate group had a 27% (OR 0.73, 95% CI 0.62, 0.87, p = 0.0003) and 53% (OR 0.47, 95% CI 0.35, 0.63, p < 0.0001) lower odds of suffering from NAFLD and AHF, respectively, compared to the low serum folate group. The similar results in propensity score matching further validated the above association. Stratified analysis showed that the negative correlation of serum folate with NAFLD and AHF demonstrated a broad consistency across populations. The results of this study indicate that higher serum folate level was associated with lower odds of NAFLD and AHF among US adults. Further prospective studies are necessary due to the limitations of cross-sectional studies.

Background Increased folic acid has been found to be latently protective against gynecological infection, including several kinds of vaginosis. In this study, we laid emphasis on whether RBC (Red Blood Cell) folate was associated with the infectious ratio of Trichomonas vaginalis, a kind of anaerobic parasitic protozoan. Methods We set RBC folate as the exposure variable and Trichomonas vaginalis as the outcome variable. Other subsidiary variables were regarded as covariates that may work as potential effect modifiers. The cross-sectional study was conducted with two merged waves of the National Health and Nutrition Examination Survey (NHANES) from 2001 to 2004, and a sample of 1274 eligible women (1212 negative and 62 positive in Trichomonas vaginalis infection) was integrated for the exploration of the association between RBC folate and Trichomonas vaginalis infection. Multivariate regression analyses, subgroup analyses, and subsequent smooth curve fittings were conducted to estimate the relationship between RBC folate and Trichomonas vaginalis in women. Results In the multivariable logistic regression analyses, a negative association was observed between stratified RBC folate status and Trichomonas vaginalis infection with all confounders adjusted. Referencing the lowest RBC folate concentration quartile, the higher concentration quartiles reported a relatively lower infection ratio, while there was a weak correlation between total RBC folate concentration and T. vaginalis (Trichomonas vaginalis) infection. In subgroup analyses stratified by BMI and age, this association was only found significant in high age and BMI groups. Conclusions The cross-sectional study indicated a negative association between RBC folic acid and Trichomonas vaginalis infection, and latent effects of BMI and age on the association were also found.