title: Relative validity and reproducibility of a diet history questionnaire in Spain. III. Biochemical markers. EPIC Group of Spain. European Prospective Investigation into Cancer and Nutrition.
abstract: BACKGROUND
  A dietary history questionnaire (DH) administered by interview was validated against 12 24-hour recalls. Relative validity of the DH and the 24-hour diet recalls was assessed by comparing nutrient intake derived from both methods with the urinary excretion of nitrogen (N) and plasma levels of carotenes, vitamin E and vitamin C.
  
  
  METHODS
  The urinary excretion of N was estimated from four 24-hour urine collections of 64 subjects (30 males and 34 females), and plasma levels of carotenes and vitamins C and E from one fasting blood collection in 72 subjects (32 men and 40 women).
  
  
  RESULTS
  The mean difference (g/day) between N excretion and N intake was -0.73 (-3.1%) for the DH and -1.4 (-8.2%) for the 24-hour diet recalls. The Pearson correlation coefficients were 0.58 and 0.52 respectively. The crude Pearson correlation coefficient between plasma level of vitamin C and dietary intake according to the DH was 0.46 and according to the 24-hour diet recall was 0.49. For beta-carotene it was 0.33 and 0.42 and for total carotenoids it was 0.27 and 0.28. For vitamin E, after adjusting for cholesterol levels and energy intake, it was 0.33 and 0.36. Some differences were found by gender and smoking habit.
  
  
  CONCLUSIONS
  The DH method gives similar results to those from the 24-hour diet recall that was used as the dietary reference method which demonstrated that DH can provide a relatively valid measurement of habitual intake for the studied nutrients.
mesh_terms: D000328:Adult; D015415:Biomarkers; D002851:Chromatography, High Pressure Liquid; D004032:Diet; D004034:Diet Surveys; D005260:Female; D006801:Humans; D008297:Male; D011939:Mental Recall; D008875:Middle Aged; D009584:Nitrogen / Q000652:urine*; D015203:Reproducibility of Results; D013030:Spain; D011795:Surveys and Questionnaires; D014815:Vitamins / Q000097:blood*
chemical_list: D015415:Biomarkers; D014815:Vitamins; D009584:Nitrogen