Increased vitamin D fortification of dairy products has increased the supply of vitamin D-containing products with different vitamin D contents on the market in Finland. The authors developed a ninety-eight-item FFQ with eight food groups and with a question on supplementation to assess dietary and supplemental vitamin D and Ca intakes in Finnish women (60ºN). The FFQ was validated in subgroups with different habitual vitamin D supplement use (0–57·5 µg/d) against the biomarker serum 25-hydroxyvitamin D (S-25(OH)D) and against 3-d food records (FR) (n 29–67). Median total vitamin D intake among participants was 9·4 (range 1·6–30·5) µg/d. Spearman’s correlations for vitamin D and Ca ranged from 0·28 (P 0·146, FFQ v. S-25(OH)D, persons not using supplements) to 0·75 (P<0·001, FFQ v. FR, supplement use included). The correlations between the FFQ and S-25(OH)D concentrations improved within increasing supplement intake. The Bland–Altman analysis showed wide limits of agreement between FFQ and FR: for vitamin D between −7·8 and 8·8 µg/d and for Ca between −938 and 934 mg/d, with mean differences being 0·5 µg/d and 2 mg/d, respectively. The triads method was used to calculate the validity coefficients of the FFQ for vitamin D, resulting in a mean of 1·00 (95 % CI 0·59, 1·00) and a range from 0·33 to 1·00. The perceived variation in the estimates could have been avoided with a longer FR period and larger number of participants. The results are comparable with earlier studies, and the FFQ provides a reasonable estimation of vitamin D and Ca intakes.

The aim of the present study was to validate the intakes of fruit, juice and vegetables from an FFQ. In sub-study I (n 147), intakes from the FFQ were evaluated against 7 d weighed food records (WR) and plasma carotenoid concentrations, whereas in sub-study II (n 85), the intakes were evaluated against plasma carotenoid concentrations and amounts of flavonoids in 24 h urine samples. Relative validity was evaluated by comparing median intakes, estimating correlation coefficients and validity coefficients using the method of triads. In sub-study I, we observed no significant difference in daily median fruit intake between the FFQ and the WR, whereas the intake of vegetables was higher from the FFQ than from the WR. The correlations between intakes from the FFQ and the WR ranged from 0·31 to 0·58. In sub-study II, the intakes of fruit and vegetables correlated significantly with plasma carotenoid concentrations and urinary flavonoids. The validity coefficients for the intakes of fruit and vegetables from the FFQ ranged from 0·61 to 0·88 in sub-study I and from 0·60 to 0·94 in sub-study II. In summary, based on the associations observed between intakes from the FFQ and the biomarkers and the FFQ validity coefficients, the FFQ was found valid and suitable for ranking individuals according to their usual intake of fruit, juice and vegetables.

The validity of fruit and vegetable intake estimated by 14 d weighed records, a twenty-seven-item food frequency questionnaire (FFQ) and a 180-item FFQ was investigated using serum carotenoids as the validity criterion. In addition, the method of triads was used to assess the validity of fruit and vegetable intake estimated from the FFQ and serum carotenoids. One hundred Norwegian men completed 14 d weighed records and the 180-item FFQ. Eighty-six of them also completed the twenty-seven item FFQ. The partial correlation coefficients between serum carotenoids and fruit and vegetable intake were slightly higher for the 14 d weighed records than for the two FFQ, but no difference was observed between the 180- and the twenty-seven item FFQ. The strongest correlations were observed between vegetable intake and serum α-carotene. The highest validity coefficients (VC) were observed for vegetable intake estimated from weighed records, the 180-item FFQ, the twenty-seven item FFQ and by the biomarker serum α-carotene, with VC of 0·77, 0·58, 0·51 and 0·67, respectively. In conclusion, the short FFQ gave as valid estimates for fruit and vegetable intake as the long FFQ. Both the estimated partial correlation coefficients and VC suggest that serum α-carotene is the best biomarker for intake of vegetable alone and total intake of fruit and vegetables in this population of Norwegian men, but the biomarkers did not perform any better than the FFQ.