Why FFQs don’t predict vitamin D status

Two recent studies used food frequency questionnaires to predict vitamin D status and later allergy (Devereux 2007 and Camargo 2007) probably the only two studies that seem to contradict the vitamin D hypothesis.
New research now reported at the ATS congress [Poster Board # A84] “Measurement of Vitamin D Levels Utilizing Laboratory and Dietary Recall Information from the Tennessee Children’s Respiratory Initiative” and published in Am J Respir Crit Care Med 181;2010:A1890 shows that FFQs don’t predict vitamin D status

We sought to: (1) validate the use of bloodspots compared to plasma or whole blood for measuring VitD levels, (2) correlate the measured levels with VitD intake estimated from dietary recall, and (3) investigate the relationship between maternal-child VitD levels … Biological mothers of infants enrolled in the larger Tennessee Children’s Respiratory Initiative cohort had VitD measurements performed by mass spectrometry on bloodspots (n=342), plasma (n=27) and whole blood (n=51) samples collected at enrollment … Intake by recall was not statistically associated with VitD levels, even after consideration for season, current smoking, education and race … These results highlight the ease and accuracy of measuring VitD levels using bloodspot cards and the inability of intake questionnaires to adequately assess levels of a vitamin that is largely affected by sun exposure.

Sorry Scott, not the Gale study is being crap … Vitamin D FFQs probably measure something else, maybe SES but not any immunological event.