Validation of a food frequency questionnaire to assess folate intake of Dutch elderly people

Abstract

Folate is required for 1-carbon metabolism and deficiency in folate leads to megaloblastic anemia. Low levels of folate have been associated with increased risk of vascular disease. To investigate whether RDA of folate are met, habitual folate intake needs to be assessed reliably. We developed a FFQ to specifically measure folate intake over the previous 3 months in elderly people in the Netherlands. Major sources of folate intake, i.e. foods contributing to at least 80 % of the average folate intake, were identified through an analysis of the second Dutch Food Consumption Survey for the sub-population of men and women aged 50 -70. In 2000 and 2001, folate intake was estimated with this questionnaire in 1286 individuals aged 50-75 years. Concentrations of serum and erythrocyte folate served as biomarkers with which relative validity of the questionnaire was assessed. The same FFQ was repeated after 3 years in 803 subjects in order to assess long-term reproducibility. Mean folate intake was estimated to be 196 (SD 69) mg/d. Spearman correlation coefficients between folate intake and serum and erythrocyte concentrations were 0·14 (P,0·01) and 0·05 (P¼ 0·06) respectively. Spearman correlations between folate intakes measured at baseline and after 3 years were 0·58 (P,0·01). 47 % of the participants were classified in the same quartiles on the two occasions. Our FFQ showed a weak correlation between folate intake and blood folate concentrations and reproducibility was acceptable. This FFQ is able to rank subjects according to their folate intake. FFQ: Folate intake: Biomarkers: Validity: ReproducibilityFolate is a B vitamin that is essential for many aspects of human health. Deficiency of this B vitamin can lead to megaloblastic anemia 1 . A suboptimal folate status can increase the risk for women to have a child with a neural tube defect 2 . Furthermore, low folate status and subsequent elevated concentrations of plasma total homocysteine (tHcy) have been associated with neurocognitive dysfunction 3 , colon cancer 4 and vascular diseases 5 . Folate is found in foods such as liver, vegetables, bread, potatoes, dairy products and fruit 6 . In the Netherlands, the RDA of folate is 300 mg for adults 7 . However, many Dutch adults do not meet this recommendation 6 .There are different methods to assess habitual nutrient intake, but so far there is no gold standard. In large-scale epidemiological studies FFQ are preferred, because they are easy to administer and measure long-term intake. We developed a FFQ to assess folate intake over the past 3 months in Dutch elderly people. Here we describe the development of this questionnaire and subsequent comparison of the folate intake data with blood folate concentrations to assess the validity of the questionnaire. Furthermore long-term reproducibility was assessed. SubjectsBaseline data of subjects from three different folate supplementation studies undertaken by our group in the past years were combined: (1) The FACIT-study 8 , a double blind, randomised, placebo-controlled i...

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