Validation of a semiquantitative food frequency questionnaire to assess folate status. Results discriminate a high-risk group of women residing on the Mexico-U.S. border

Abstract

Background. The purpose of the study was to estimate dietary intake of folate in two groups of women from different economic backgrounds and to evaluate validity of the 5-day-weighed food registry (5-d-WFR) and Food Frequency Questionnaire (FFQ) using biological markers. Methods. A cross-sectional study was conducted in two samples of urban Mexican women: one represented the middle socioeconomic status (middle SES) and the other, low socioeconomic status (low SES). Middle SES included 34 women recruited from 1998 to 1999. Participants were between the ages of 18 and 32 years and were employed in the banking industry (middle SES) in the U.S.-Mexican border city of Tijuana, Baja California. Low SES included 70 women between the ages of 18 and 35 years recruited during the year 2000. These women were receiving care at a primary health care center in Ensenada, Baja California Norte State, Mexico (low SES). Pearson correlations were calculated between folate intake among 5-day diet registry, FFQ, and biochemical indices. FFQ reproducibility was performed by Spearman correlation of each food item daily and of weekly intake. Results. Average folate intake in middle SES from 5-d-WFR was 210 μg±171. Fifty four percent of participants had intakes <200 μg/daily. Average folate intake from FFQ was 223±78 μg/day. Pearson correlation between log transformed and within individually adjusted 5-d-WFR folate intakes and serum folate was 0.40 ( p = 0.02). Discussion. Mexican women of reproductive age living in the U.S.-Mexican border State of Baja California are at very high risk of NTDs as a result of low folate intake and low serum folate and RBC folate concentrations.