VALIDITY OF RETROSPECTIVE DIET HISTORY: ASSESSING RECALL OF MIDLIFE DIET USING FOOD FREQUENCY QUESTIONNAIRE IN LATER LIFE

Limited information exists on the validity of dietary information given by elderly people on their past diet. Here we test the relative validity of a food frequency questionnaire asking older persons about their midlife diet. Design: Retrospective food intake of 56-72-year-old subjects was estimated using a food frequency questionnaire designed for the AGES-Reykjavik Study (AGES-FFQ), an epidemiological study of older individuals. Results were compared with detailed dietary data gathered from the same individuals 18-19 years previously, i.e., in midlife, as part of a national cohort. Spearman correlation and cross-classifications were used to assess the ability of the AGES-FFQ to rank subjects according to their intake. Setting: Nationwide, Iceland. Participants: Subjects, born 1937-1952 (n=174), who participated in the 1990 Icelandic National Dietary Survey. Measurements: Dietary intake, estimated by the AGES-FFQ (2008-2009), and dietary history obtained from the 1990 Icelandic National Dietary Survey as a reference method. Results: The strongest correlation between the AGES-FFQ and the reference method was found for cod liver oil, r=0.53, p<0.001 and r=0.56, p<0.001, for men and women, respectively. For men the corresponding correlation coefficient for milk and dairy products was r=0.43, p<0.001. The correlation coefficients were lower but within a reasonably acceptable range (r=0.26-0.40) for meat, fish and potatoes for both genders, as well as fresh fruits and milk/dairy products for women and whole-wheat bread, oatmeal/muesli and blood/liver-sausage for men. No correlation was found between the AGES-FFQ and the dietary history for rye bread and vegetable consumption. Subjects were categorized into five groups according to level of consumption by the two methods. Cross-classification showed that 16-59% were classified into same group and 43-91% into same or adjacent group, 0-14% were grossly misclassified into opposite groups. Conclusion: The AGES-FFQ on midlife diet was found suitable to rank individuals by their intake of several important food groups.