title: The impact of folic acid intake on the association among diabetes mellitus, obesity, and spina bifida.
abstract: OBJECTIVE
  The purpose of this study was to investigate the relationship between spina bifida and 2 established risk factors (pregestational diabetes mellitus and obesity) in both the presence and absence of the recommended daily folic acid intake in the periconceptional period.
  
  
  METHODS
  Cases of spina bifida (n = 1154) and control subjects (n = 9439) from the Slone Epidemiology Center Birth Defects Study (1976-2011) were included. Information on preexisting diabetes mellitus (collected 1976-2011) and obesity (collected 1993-2011), defined as a body mass index of ≥30 kg/m(2), was collected through interviews that were conducted within 6 months of delivery. Periconceptional folic acid intake was calculated with both dietary and supplement information. Mothers were classified as consuming more or less than 400 μg/day of folic acid; food folate was included at a 30% discount for its lower bioavailability. Logistic regression models that were adjusted for maternal age, race, education, and study site were used to calculate adjusted odds ratios (aORs) and 95% confidence intervals (CIs) for the joint effects of low folic acid intake coupled with diabetes mellitus or obesity.
  
  
  RESULTS
  Case mothers were more likely to have diabetes mellitus or be obese (0.7% and 19.0%, respectively) than control mothers (0.4% and 10.8%, respectively). The joint effect of diabetes mellitus and lower folic acid intake on spina bifida was larger (aOR, 3.95; 95% CI, 1.56-10.00) than that of diabetes mellitus and higher folic acid intake (aOR, 1.31; 95% CI, 0.17-10.30). Folic acid intake made little difference on the association between obesity and spina bifida.
  
  
  CONCLUSIONS
  Our findings suggest that folic acid further attenuates, although does not eliminate, the risk of spina bifida that is associated with diabetes mellitus than the risk with obesity.
authors.affiliation: Slone Epidemiology Center, Boston University, Boston, MA 02215, USA. separker@bu.edu
authors.forename: Samantha E
authors.initials: SE
authors.lastname: Parker
authors.forename: Mahsa M
authors.initials: MM
authors.lastname: Yazdy
authors.forename: Sarah C
authors.initials: SC
authors.lastname: Tinker
authors.forename: Allen A
authors.initials: AA
authors.lastname: Mitchell
authors.forename: Martha M
authors.initials: MM
authors.lastname: Werler
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D048909:Diabetes Complications / Q000209:etiology*; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage*; D006801:Humans; D016015:Logistic Models; D009765:Obesity / Q000150:complications*; D012307:Risk Factors; D016135:Spinal Dysraphism / Q000209:etiology*
chemical_list: D005492:Folic Acid
keywords: folic acid; obesity; preexisting diabetes mellitus; pregnancy; spina bifida