title: A quantile regression approach can reveal the effect of fruit and vegetable consumption on plasma homocysteine levels.
abstract: A reduction in homocysteine concentration due to the use of supplemental folic acid is well recognized, although evidence of the same effect for natural folate sources, such as fruits and vegetables (FV), is lacking. The traditional statistical analysis approaches do not provide further information. As an alternative, quantile regression allows for the exploration of the effects of covariates through percentiles of the conditional distribution of the dependent variable.
  
  
  
  To investigate how the associations of FV intake with plasma total homocysteine (tHcy) differ through percentiles in the distribution using quantile regression.
  
  
  
  A cross-sectional population-based survey was conducted among 499 residents of Sao Paulo City, Brazil. The participants provided food intake and fasting blood samples. Fruit and vegetable intake was predicted by adjusting for day-to-day variation using a proper measurement error model. We performed a quantile regression to verify the association between tHcy and the predicted FV intake. The predicted values of tHcy for each percentile model were calculated considering an increase of 200 g in the FV intake for each percentile.
  
  
  
  The results showed that tHcy was inversely associated with FV intake when assessed by linear regression whereas, the association was different when using quantile regression. The relationship with FV consumption was inverse and significant for almost all percentiles of tHcy. The coefficients increased as the percentile of tHcy increased. A simulated increase of 200 g in the FV intake could decrease the tHcy levels in the overall percentiles, but the higher percentiles of tHcy benefited more.
  
  
  
  This study confirms that the effect of FV intake on lowering the tHcy levels is dependent on the level of tHcy using an innovative statistical approach. From a public health point of view, encouraging people to increase FV intake would benefit people with high levels of tHcy.
authors.affiliation: Department of Epidemiology, Institute of Social Medicine, Rio de Janeiro State University, Rio de Janeiro, Brazil.
authors.forename: Eliseu
authors.initials: E
authors.lastname: Verly
authors.affiliation: Department of Nutrition, School of Public Health, Sao Paulo University, São Paulo, Brazil.
authors.forename: Josiane
authors.initials: J
authors.lastname: Steluti
authors.affiliation: Department of Nutrition, School of Public Health, Sao Paulo University, São Paulo, Brazil.
authors.forename: Regina Mara
authors.initials: RM
authors.lastname: Fisberg
authors.affiliation: Department of Nutrition, School of Public Health, Sao Paulo University, São Paulo, Brazil.
authors.forename: Dirce Maria Lobo
authors.initials: DM
authors.lastname: Marchioni
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D004435:Eating; D005260:Female; D005492:Folic Acid / Q000097:blood; D005638:Fruit; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D014675:Vegetables
chemical_list: D006710:Homocysteine; D005492:Folic Acid