Validation of an FFQ to assess antioxidant intake in overweight postmenopausal women

Objective: To validate an FFQ to assess antioxidant intake in overweight postmenopausal women. Design: A seventy-four-item antioxidant 1-month FFQ was developed based on major antioxidant sources in the American diet. Forty overweight postmenopausal women participated in a 9-month observational study and completed four sets of FFQ and 7 d food record (7dFR) every 3 months. Twelve-hour fasting blood was collected for plasma antioxidant measurement at the first visit. Setting: Connecticut, USA. Subjects: Forty overweight postmenopausal women. Results: Spearman correlation coefficients of 1-month antioxidant intake estimated from the first set of FFQ and 7dFR ranged from 0.34 to 0.87, except for gamma-tocopherol. The proportion of participants categorized into the extremely opposite tertiles averaged 7%. Significant correlations were observed for diet-plasma vitamin C, a-tocopherol and carotenoids (P<0.05). No time effect was observed on the dietary antioxidant intakes estimated from four 7dFR and four FFQ. Dietary antioxidants estimated from averaged four 7dFR showed moderate to high correlation with those estimated from averaged four FFQ and from each FFQ collected every 3 months. Bland-Altman plots did not show any systematic bias. Averaged misclassifications were below 10% between these two instruments. Conclusions: These findings attested a reasonable validity and a good acceptance of this 1-month FFQ in assessing both short-term and long-term diverse antioxidant intakes in these overweight postmenopausal women. The use of this FFQ in associating antioxidant intake with disease risk needs further investigation.