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Abbreviations: tHcy, total homocysteine
Folate is a B vitamin that is essential for many aspects of human health. Deficiency of this B vitamin can lead to megaloblastic anemia1 . A suboptimal folate status can increase the risk for women to have a child with a neural tube defect2 . Furthermore, low folate status and subsequent elevated concentrations of plasma total homocysteine (tHcy) have been associated with neurocognitive dysfunction3 , colon cancer4 and vascular diseases5 . Folate is found in foods such as liver, vegetables, bread, potatoes, dairy products and fruit6 . In the Netherlands, the RDA of folate is 300 μg for adults7 . However, many Dutch adults do not meet this recommendation6 .
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.
Subjects
Baseline data of subjects from three different folate supplementation studies undertaken by our group in the past years were combined: (1) The FACIT-study8 , a double blind, randomised, placebo-controlled intervention study on the effect of 3 years supplementation with 0·8 mg folic acid/d on age-related diseases (carotid artery intima-media thickness, cognitive function and hearing); (2) the Dolfin-study9 , a dose-response trial with a randomised, double blind, parallel-group, placebo-controlled design aiming to find the lowest dose of folic acid that maximally lowers tHcy concentrations, and (3) the CHEF-study10 , a placebo-controlled, randomised parallel trial to study relative bioavailability of polyglutamated folic acid v . monoglutamated folic acid. The study populations consisted of 819, 308 and 182 subjects, respectively. Twenty-three subjects participated in Dolfin as well as in CHEF. We decided to use their data from Dolfin, as in Dolfin MTHFR genotypes, which influence folate status, have also been determined. Five subjects were excluded from further analyses because of missing values on the FFQ. Altogether, complete data...