A comparison of American and Canadian RBC folate concentrations

In North America, folic acid fortification and supplementation policies have improved folate status and reduced the incidence of poor birth outcomes. This research aimed to compare RBC folate (RBF) concentrations in two nationally representative surveys: the 2007–2008 US NHANES and the 2007–2009 Canadian Health Measures Survey (CHMS). RBF was assessed in participants aged 6 to 79 years and in a subset of women of childbearing age (WCBA). Two different folate assay methods were employed— microbiologic assay (NHANES) and Immulite 2000 immunoassay (CHMS)—necessitating the application of a conversion equation to adjust the CHMS RBF data. T‐tests were used to examine country differences. RBF concentrations ≥906 nmol/L (considered optimal for neural tube defect risk reduction) were explored with a multiple logistic regression model. Median Canadian RBF (adjusted) were lower than those of Americans (988 nmol/L and 1106 nmol/L, respectively), but unadjusted Canadian median RBF values were higher (1248 nmol/L). Canadian WCBA (adjusted RBF) were less likely than American WCBA to have RBF ≥906 nmol/L (OR 0.58; 95% CI 0.37, 0.92), though Canadian WCBA with unadjusted RBF values were more likely to achieve this cut‐off than American WCBA (OR 1.90; 95% CI 1.03, 3.49). Harmonization of folate measurement procedures in future surveillance efforts would support comparisons and inform policy directions. Grant Funding Source : Canadian Institutes for Health Research Fellowship (180375) to C.K.C and Operating Grant (218776) to M.S.T, D.L.O and C.K.C.