Validation of dietary assessment methods in the UK arm of EPIC using weighed records, and 24-hour urinary nitrogen and potassium and serum vitamin C and carotenoids as biomarkers.
BACKGROUND
In the UK EPIC validation studies, the accuracy of several methods was assessed by comparison with to-day weighed records and the biomarkers, 24-hour urine nitrogen (N) and potassium (K), plasma carotenoids and plasma vitamin C.


METHODS
Comparisons between methods were made on 156 women, studied over 1 year at 3-monthly intervals at home. On each of four occasions, volunteers completed 4 days of weighed records and provided two 24-hour urine collections and a fasting blood sample.


RESULTS
In comparison with the 16 days of weighed records, a food frequency questionnaire (FFQ) yielded higher values mainly due to greater reported consumption of milk and of vegetables. A 24-hour recall was as good as the FFQ in placing individuals in the distribution of habitual diet from weighed records. Results obtained from a 7-day estimated record were closest to those obtained from the weighed record. Correlations between 24-hour urine excretion and dietary N intake from weighed records were high (0.78-0.87) as were those with estimated food diaries (0.60-0.70). Correlations between urine N and the FFQ and 24-hour recall were lower (0.10 to 0.27), but improved by energy adjustment using residuals for N and K which are correlated with total energy intake. Comparisons between dietary estimates and urinary K and serum carotenoids and vitamin C showed broadly similar results. Limited biomarker information amongst 200 UK EPIC participants supported the findings of the validation study.


CONCLUSIONS
UK EPIC uses three methods (the 7-day diary, an improved FFQ, and the 24-hour recall) to assess diet. 93% of first food diaries are returned completed by participants. Repeated diaries are the main dietary assessment method for nested case-control analyses.
Bingham
S A
SA
MRC Dunn Clinical Nutrition Centre, Cambridge, UK.
Gill
C
C
Welch
A
A
Cassidy
A
A
Runswick
S A
SA
Oakes
S
S
Lubin
R
R
Thurnham
D I
DI
Key
T J
TJ
Roe
L
L
Khaw
K T
KT
Day
N E
NE
D000368:Aged; D001205:Ascorbic Acid / Q000097:blood*; D015415:Biomarkers; D002338:Carotenoids / Q000097:blood*; D015331:Cohort Studies; D004032:Diet; D004034:Diet Surveys; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans; D011939:Mental Recall; D008875:Middle Aged; D009584:Nitrogen / Q000652:urine*; D011188:Potassium / Q000097:blood*; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D006113:United Kingdom
D015415:Biomarkers; D002338:Carotenoids; D009584:Nitrogen; D001205:Ascorbic Acid; D011188:Potassium