Validating Polyphenol Intake Estimates From a Food‐Frequency Questionnaire Using Repeated 24‐Hour Dietary Recalls and a Unique Method of Triads Approach With Two Biomarkers

Assessment of polyphenol intake in free‐living subjects is challenging, mostly because of the difficulty in accurately measuring phenolic content and the wide presence of phenolic compounds in foods. The aim of this study was to evaluate the validity of polyphenol intake estimated from food‐frequency questionnaires (FFQ) and urinary polyphenol excretion in a sample of Adventist Health Study‐2 (AHS‐2) participants with a diverse range of dietary intakes. Dietary intake data from 899 adults (43% black and 67% female) were obtained. Polyphenol intake estimates from FFQ and urinary excretion of total polyphenols (TUP) measured using Folin‐Ciocalteau assay were compared to the mean of six measurements of 24‐hour dietary recalls (24‐HR) as reference. Pearson correlation coefficients ( r ), corrected for attenuation from within‐person variation in the recalls, were calculated for 24‐HR and FFQ and 24‐HR and TUP. Further, we applied the method of triads to assess validity coefficients between dietary assessment tools, TUP, and plasma carotenoids. The mean polyphenol intake values were 717 ± 646 mg/d from FFQs and 402 ± 345 mg/d from 24‐HR. In crude models, total dietary polyphenol intake from 24‐HR was correlated with FFQ ( r = 0.51, p < 0.001), TUP ( r = 0.15, p < 0.001), and with plasma carotenoids ( r = 0.14, p < 0.001). Deattenuation for within‐person variability on the recalls improved correlations between 24‐HR and FFQ ( r = 0.64, 95% CI = 0.61, 0.69 ) and TUP ( r = 0.19, 95% CI = 0.09, 0.20). Correlations between 24‐HR and FFQ were higher for non‐blacks than blacks, but correlations between 24‐HR and biomarkers were higher for blacks compared to non‐blacks. In the triad model including the FFQ, TUP and plasma carotenoids, the validity coefficient between the FFQ and theoretical true intake was 0.46 (95% CI 0.20, 0.93). The AHS‐2 FFQ is a reasonable indicator of total polyphenol intake in the AHS‐2 cohort. Unlike most previous validation studies, our application of the method of triads incorporated two biomarkers, which minimized bias associated with comparing two self‐reported dietary assessments. Because biomarkers are influenced by genetic variance, metabolism, and bioavailability, they should be used as additional measures rather than as a replacement to dietary intake assessment. Support or Funding Information This work was supported by National Cancer Institute grant 1U01CA152939, the McLean Endowment, and the Hulda Crooks Grant. The funding agencies had no role in the design and analysis of the study or in the writing of this article. 1 General descriptives of study subjects (n = 899)1CharacteristicsAge, mean (SD) 58.2 (13.3)Sex (% female) 66.5Race (%)Black 43.1 Non‐black 56.9BMI (%)Underweight or normal weight (18.5 to 24.9) 40.4 Overweight (25 to 29.9) 34.4 Obese (> 30) 25.2Energy intake (kcal/d) from FFQ, mean (SD) 1887 (755)Energy intake (kcal/d) from 24‐HR, mean (SD) 1555 (492)Renal function (%) 2Normal 99 Impaired < 1Urinary creatinine (g/L), mean (SD) 0.69 (0.58)Total dietary polyphenol intake from 24‐IIR (mg/d), 3 mean (SD) 402 (345)Total dietary polyphenol intake from short FFQ (mg/d), 3 mean (SD) 717 (646)Total urinary polyphenols (mg GAE/g creatinine), mean (SD) 108 (98.9)Total plasma carotenoids (μg/L), mean (SD) 1.6 (1.0)1 Proportion of missing data: age, 8%, sex, 7.4%, race, 8.4%, BMI, 7.8%, renal function, 24% urinary creatinine, 24%, total urinary polyphenols, 29%, plasma carotenoids, 9.8%. 2 Renal function defined as normal renal function: ≥ 60 mL/min or impaired renal function < 60 mL/min. 3 Unadjusted intake estimates are presented. FFQ, food frequency questionnaire; 24‐HR, 24‐hour dietary recall; GAE, gallic acid equivalent.2 Uncorrected, unadjusted deattenuated, and adjusted deattenuated correlations between energy‐adjusted TDP from 24‐HR and TDP from FFQ, total urinary polyphenol biomarker, and total plasma carotenoids, stratified by race 1TDP FFQ (mg/d) TUP (mg GAE/g urinary creatinine) 3 Plasma carotenoids (μg/L) 3Uncorrected correlation Deattenuated unadjusted correlation (95% CI) Deattenuated adjusted correlation (95% CI) 4 Uncorrected correlation Deattenuated unadjusted correlation (95% CI) Deattenuated adjusted correlation (95% CI) 4 Uncorrected correlation Deattenuated unadjusted correlation (95% CI) Deattenuated adjusted correlation (95% CI) 4All 0.51* 0.64 (0.55, 0.71) 0.63 (0.61, 0.69) 0.15* 0.19 (0.09, 0.29) 0.20 (0.13, 0.32) 0.14* 0.18 (0.10, 0.27) 0.18 (0.12, 0.27)Non‐blacks 0.58* 0.71 (0.54, 0.81) 0.71 (0.64, 0.81) 0.14* 0.16 (0.04, 0.27) 0.17 (0.07, 0.30) 0.12* 0.14 (0.03, 0.26) 0.13 (0.03, 0.24)Blacks 0.38* 0.52 (0.36, 0.66) 0.52 (0.47, 0.66) 0.17* 0.23 (0.05, 0.45) 0.23 (0.09, 0.42) 0.21* 0.28 (0.13, 0.42) 0.29 (0.20, 0.44)1 Sig. at the *0.001 level (2‐tailed). 4 Adjusted for age, race, gender, and BMI. TDP, intake of total dietary polyphenols; 24‐HR, 24‐hour dietary recalls; FFQ, food frequency questionnaire; TUP, total urinary polyphenols; GAE, gallic acid equivalents.3 Validity coefficients and 95% confidence intervals between true intake (T) and polyphenol intakes from food frequency questionnaire (Q), 24‐HR (R), and biomarkers total urinary polyphenols (M) and plasma carotenoids (P), calculated using method of triads 1VC 95% CIFFQ (Q, T) 2 0.46 0.20, 0.93 TUP (M, T) 0.18 0.04, 0.32 Plasma carotenoids (P.T) 0.49 0.25, 1.00 24‐HR (R, T) 2 0.38 0.15, 0.96 TUP (M, T) 0.29 0.10, 0.66 Plasma carotenoids (P. T) 0.30 0.09, 0.601 Correlations adjusted for age, race, gender and BMI. BCa confidence interval based on 2000 resampling. * Estimated upper limit exceeds 1 and was thus set to 1.00.