The development and evaluation of a food frequency questionnaire used in assessing vitamin D intake in a sample of healthy young Canadian adults of diverse ancestry

Little data exist on vitamin D deficiency related with intake, especially for the Canadian population. The purpose of this study was to develop and evaluate a food frequency questionnaire (FFQ) with 37 items for rapid assessment of vitamin D intake in healthy young adults of diverse ancestry. We recruited 107 subjects in Southern Ontario during the late winter of 2007 who completed an FFQ twice (FFQ-1 and FFQ-2, repeated for reproducibility assessment) and a 7-day food diary (for validation). Serum 25-hydroxyvitamin D (25(OH)D), the major biomarker of vitamin D nutritional status, and skin melanin were determined. The FFQ results were highly correlated with 7-day diary results and with serum 25(OH)D concentrations (r = 0.529, P < .001; r = 0.481, P < .001, respectively). Modifications to the FFQ, by redefining the large serving size and excluding the fortified orange juice category, improved the validity of the FFQ (r = 0.602, P < .001; r = 0.520, P < .001, respectively). The FFQ results were highly correlated (r = 0.663, P < .001), but the mean intakes were different (P < .05). Using results from a modified version of FFQ-1, we examined dietary intakes in 3 predominant groups: East Asian (n = 27), European (n = 31), and South Asian (n = 32). The European group had higher total vitamin D intake (P < .05) and the highest serum 25(OH)D concentrations (P < .05), with a trend for dairy products being responsible for this (P < .10). Because Canadians are reliant on dietary intakes of vitamin D in the wintertime, especially those with higher skin melanin, our FFQ can monitor and provide information on intake and food group consumption.