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Background A well-designed, validated quantitative food frequency questionnaire ( FFQ) could offer an efficient and cost-effective method for assessing habitual vitamin D intake. The present study aimed to describe the development, validation and implementation of a vitamin D FFQ. Methods National food consumption survey data obtained from Irish adults (18-64 years) were used to identify foods that contribute 95% of vitamin D intake. A winter-based validation study was carried out for the resulting FFQ in 120 females, including 98 women [mean (SD) 65.0 (7.3) years] and 22 girls [12.2 (0.8) years], using a 14-day diet history ( DH) as a comparator. Serum 25( OH)D concentrations were analysed. Validity coefficients were calculated using the method of triads. Cross-classification and Bland-Altman analysis were also performed. Results Median (interquartile range) vitamin D intakes (including the contribution from nutritional supplements) were 5.4 (3.7) and 3.7 (5.9) μg day−1 from the FFQ and DH, respectively and intakes of vitamin D from food sources were 3.6 (3.1) and 2.4 (2.2) μg day−1. The FFQ and DH classified 86% and 87% of individuals into the same and adjacent thirds of wintertime serum 25( OH)D status, respectively. There was a strong association ( r = 0.71, P < 0.0001) and no significant systematic or proportional bias observed for the difference between estimates from the FFQ and DH. The validity coefficient for the FFQ was 0.92 (95% confidence interval = 0.80-0.97). Repeatability analysis ( n = 56) performed 6-12 months later showed no significant difference in estimates of vitamin D between administrations. Conclusions The data obtained in the present study indicate high validity and good reproducibility of a short, interviewer-administered FFQ for vitamin D. [ABSTRACT FROM AUTHOR]

Background: The relative potency of 25-hydroxyvitamin D3 to vitamin D3 needs to be better defined so that food-composition tables can better reflect the true vitamin D nutritive value of certain foods. Objective: We performed a randomized, controlled intervention study in apparently healthy, free-living adults to investigate whether the intake of 25-hydroxyvitamin D3 is 5 times more potent in raising serum 25-hydroxyvitamin D [25(OH)D] during winter compared with an equivalent amount of vitamin D3. Design: A randomized, placebo-controlled, double-blind intervention study was conducted in adults aged ≥50 y (n = 56) who consumed a placebo, 20 µg vitamin D3, or 7 or 20 µg 25-hydroxyvitamin D3 daily throughout 10 wk of winter. Serum 25(OH)D was measured by using an enzyme-linked immunoassay, and serum albumin-corrected calcium (S-Ca) was assessed colorimetrically at the baseline, midpoint, and endpoint of the study. Results: The mean (±SD) increases (per microgram of vitamin D compound) in serum 25(OH)D concentrations over baseline after 10 wk of supplementation were 0.96 ± 0.62, 4.02 ± 1.27, and 4.77 ± 1.04 nmol • L-1 • µg intake-1 for the 20-µg vitamin D3/d and 7- and 20-µg 25-hydroxyvitamin D3/d groups, respectively. A comparison of the 7- and 20-µg 25-hydroxyvitamin D3/d groups with the 20-µg vitamin D3/d group yielded conversion factors of 4.2 and 5, respectively. There was no effect of treatment on S-Ca concentrations and no incidence of hypercalcemia (S-Ca >2.6 nmol/L). Conclusions: Each microgram of orally consumed 25-hydroxyvitamin D3 was about 5 times more effective in raising serum 25(OH)D in older adults in winter than an equivalent amount of vitamin D3. This conversion factor could be used in food-compositional tables for relevant foods. This study was registered at clinicaltrials.gov as NCT01398202. [ABSTRACT FROM AUTHOR]

Background/Aims: To explore associations between vitamin D and cardiovascular disease risk factors in young European adults. Methods: This was a cross-sectional analysis of serum 25-hydroxyvitamin D [s25(OH)D], intact parathyroid hormone (iPTH) and biomarkers of cardiovascular disease risk in 195 healthy 20- to 40-year-olds (109 women) with a BMI between 27.5 and 32.5 from Iceland (64°N; n = 82), Ireland (51°N; n = 37) and Spain (42°N; n = 76) during mid-late winter. Results: The median s25(OH)D was 52.8 nmol/l (IQR 38.1-69.9) or 21.1 ng/ml (IQR 15.2-28.0) with a latitude-dependent gradient (p ≤ 0.0001): Iceland, 41.7 nmol/l (IQR 32.7-54.2) or 16.7 ng/ml (IQR 13.1-21.7); Ireland, 52.9 nmol/l (IQR 35.3-68.6) or 21.2 ng/ml (IQR 14.1-27.4), and Spain, 67.1 nmol/l (IQR 47.1-87.1) or 26.8 ng/ml (IQR 18.8-34.8). Eleven percent of Icelandic participants had s25(OH)D concentrations <25 nmol/l (10 ng/ml) and 66% of Icelandic, 43% of Irish, and 30% of Spanish volunteers had concentrations <50 nmol/l (20 ng/ml), respectively. Overall, 17% met 3 or more of the NCEP/ATP III criteria for cardio-metabolic syndrome (MetS). Participants in the lowest third of s25(OH)D [≤42.5 nmol/l (17 ng/ml)] were more likely to have MetS (OR 2.49, p = 0.045) and elevated TAG (OR 3.46, p = 0.019). Individuals with iPTH concentrations in the lowest third [2.34 pmol/l (22.2 pg/ml)] were more likely to have elevated fasting TAG (OR 4.17, p = 0.039), insulin (OR 3.15, p = 0.029) and HOMA-IR (OR 2.15, p = 0.031), and they were less likely to have elevated IL-6 (OR 0.24, p = 0.003). Conclusion: There were interactions between s25(OH)D, iPTH and cardio-metabolic risk factors which, given the increasing prevalence of overweight and obesity and a low vitamin D status among adults, require randomised controlled vitamin D intervention studies in overweight persons. Copyright © 2011 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]