Changes in vitamin D status of overweight and obese 6 to 12- year old children: Results from a 1 year, family-centred lifestyle intervention

Background: Vitamin D status is lower in Canadian children who are overweight or obese compared to children of healthy weights.Objective: The objectives of this study are 1) to determine the vitamin D status of overweight and obese children, 2) to examine the association between changes in fat mass (FM) and vitamin D status, and 3) to determine if there is a relationship between regional adiposity and blood concentrations of 25-hydroxyvitamin D (25(OH)D).Methods: Data was collected at baseline, and then every 3 months for a one year period, from participants enrolled in the McGill Youth and Lifestyle Intervention with Food and Exercise (MYLIFE) study (NCT01290016); healthy children aged 6-12 y with body mass index (BMI)-for-age >85th percentile were included.Chemiluminescence immunoassay was used to measure plasma 25(OH)D.Standard measurements of weight, height and waist circumference (WC) were taken at each visit; BMI and BMI z-scores were calculated (WHO AnthroPlus, Geneva, Switzerland, 2009).Body composition was measured using dual-energy X-ray absorptiometry to determine whole body and regional adiposity.Z-scores for adiposity indicators were calculated based on reference data from the National Health and Nutrition Examination Survey; children were then separated into tertiles based on these z-scores.Constitutive and facultative skin pigmentation was measured using a hand-held spectrophotometer in order to determine Fitzpatrick skin types.Children were categorized according to cutaneous UVB synthesis period.Ethnicity was self-disclosed and pubertal status was reported at baseline and categorized according to Tanner stages.Differences in 25(OH)D among tertiles of each adiposity indicator (eg: % body fat (%BF), FM, WC) were tested using a mixed model ANOVA.Logistic v regression was used to determine the odds ratio of not meeting recommended 25(OH)D cutoffs.Results: Data from 101 children (46 boys and 55 girls) were used in this study.The mean 25(OH)D concentration at baseline was 59.8 ± 1.3 nmol/L, with no significant difference between sexes (p=0.740).Boys had lower %BF (p=0.012),greater BMI z-scores (p=0.001) and greater WC (p=0.013)than girls.After one year, those who decreased FM appeared to have better plasma 25(OH)D than those who maintained or gained FM (59.2 vs. 55.3 nmol/L; p=0.310), although significance was not reached.Every kg increase in FM was associated to increased odds of not reaching plasma 25(OH)D cutoffs of 75 nmol/L (OR: 1.2, 95% CI: 1.1-1.4,p=0.006).Arm fat (OR: 2.6, 95% CI: 1.3-5.2,p=0.009) was associated to greater odds of missing the cutoff than leg fat (OR: 1.6, 95% CI: 1.1-2.3,p=0.009).Android:gynoid fat patterning was not significant (p=0.066).Conclusion: Adiposity in overweight and obese children, irrespective of location, has an inverse relationship with vitamin D status.Therefore, adiposity likely needs to be considered when establishing dietary intake recommendations to match population cutoffs for vitamin D status.Future large-scale longitudinal research is required to examine if a reduction in FM would lead to a significant increase in vitamin D status.viRésumé Contexte: Le statut en vitamine D est plus faible chez les enfants canadiens en surpoids ou obèses, comparativement aux enfants de poids normal.Objectif: Les objectifs de cette étude sont 1) de déterminer le statut en vitamine D des enfants en surpoids et obèses, 2) d'examiner l'association entre l'évolution de la masse adipeuse (MA) et le niveau en vitamine D, et 3) de déterminer s'il existe une relation entre l'adiposité régionale et le concentration sanguine de 25-hydroxyvitamine D (25(OH)D).Méthode: Les données ont été recueillies au début de l'étude, et ensuite tous les 3 mois pour une période d'un an, parmi les participants de l'étude McGill Youth and Lifestyle Intervention with Food and Exercise (MYLIFE) (NCT01290016), comprenant des enfants en bonne santé âgés de 6 à12 ans avec un indice de masse corporelle (IMC) pour l'âge > 85ème percentile.La chimiluminescence immunologique a été utilisée pour mesurer la concentration de 25(OH)D dans le plasma.Des mesures habituelles de poids, de taille et du tour de taille (TT) ont été prises à chaque visite; l'IMC et le score Z ont été calculés (OMS AnthroPlus, Genève, Suisse, 2009).La composition corporelle a été mesurée à l'aide de l'absorption bi-photonique à rayons X pour déterminer l'adiposité du corps et de certaines régions.Les scores Z pour les indicateurs de l'adiposité ont été calculés en utilisant les données du National Health and Nutrition Examination Survey; les enfants ont ensuite été séparés en tertiles selon ces scores Z. La pigmentation de la peau constitutive et facultative a été mesurée à l'aide d'un spectrophotomètre à main afin de déterminer la classification du type de peau de Fitzpatrick.Les enfants ont été classés selon la période de synthèse UVB cutanée.L'ethnicité a été auto-révélée et le statut vii pubertaire a été déterminé au début et classé en fonction de stades de Tanner.Les différences du 25(OH)D parmi les tertiles de chaque indicateur d'adiposité (ex: % graisse corporelle (%GC), MA, TT) ont été testées à l'aide d'un modèle ANOVA mixte.Une régression logistique a été utilisée pour déterminer la probabilité de ne pas atteindre les seuils recommandé de 25(OH)D.Résultats: Les données de 101 enfants (46 garçons et 55 filles) ont été utilisées dans cette étude.La concentration de 25(OH)D moyenne à l'inclusion était de 59,8 ± 1,3 nmol/L, sans différence significative entre les sexes (p=0,740).Les garçons avaient un plus faible %GC (p=0,012), un score Z de l'IMC plus élevé (p=0,001) et un tour de taille plus élevé (p=0,013) que les filles.Après un an, ceux qui avaient diminué leur MA ont eu une meilleure concentration de 25(OH)D dans leur plasma que ceux qui ont maintenu ou augmenté leur MA (59,2 vs 55,3 nmol/L, p=0,310).Chaque augmentation d'un kilogramme de la MA a été associée à une augmentation des chances de ne pas parvenir à la valeur-cible de 25(OH)D dans le plasma de 75 nmol/L (OR: 1,2 95%; IC: 1,1-1,4; p=0,009).Le gras dans les bras: (OR: 2.6; 95% CI: 1,3-5,2; p=0,009) est associé à des chances augmentées de ne pas atteindre la valeur cible de 25(OH)D comparativement au gras dans les jambes (OR: 1,6; 95% CI: 1,1-2,3; p=0,009).La distribution du gras de type androïd ou gynoïde n'était associée à aucune association significative (p=0,066).Conclusion: Cette étude démontre une tendance d'une l'amélioration du statut en vitamine D lorsque l'adiposité diminue.Elle démontre que le gras présent dans les membres est associé avec un statut plus pauvre en vitamine D. Une étude longitudinale à grande échelle serait nécessaire pour examiner si une diminution de l'adiposité conduit à une amélioration significative du niveau de vitamine D dans le sang.viii Authors' contributions P. Kasvis was the primary author of this thesis.During the study period, P. Kasvis was responsible for scheduling and confirming study appointments for several families.On clinic days, P. Kasvis was present to 1) measure weight, height, waist circumference, skin pigmentation of participants; 2) administer questionnaires; 3) provide basic nutrition counselling based on Canada's Food Guide to control families; 4) provide counselling sessions based on the intervention protocol of the study to both intervention and control families.P. Kasvis was also involved in creating handouts/tools to assist families meet intervention goals.Upon graduation of each family, P. Kasvis administered an exit survey and entered the data.Outside study visits, P. Kasvis was involved in entry and dietary analysis of collected food diaries.P. Kasvis was also responsible for the data entry and auditing of demographic, anthropometric, dual-energy x-ray absorptiometry (DXA), sun exposure, spectrophotometer and various biochemical data.P. Kasvis assisted in the biochemical analysis of plasma 25(OH)D, parathyroid hormone, osteocalcin and bone-specific alkaline phosphatase using the chemiluminescence immunoassay.P. Kasvis conducted the research and wrote the literature review, performed all the statistical analyses and wrote the manuscript presented in this document.T. Cohen was responsible for the design and recruitment of the study.T. Cohen was responsible for the creation of the questionnaires and teaching tools administered at each visit.In addition to performing the same tasks as P. Kasvis during study visits, T.Cohen also performed DXA scans on a number of participants.T. Cohen was responsible for entry and dietary analysis of collected food diaries and data entry/auditing of several ix questionnaires.S.E.Loiselle was responsible for recruitment of study participants.S.E.Loiselle performed the same study visit duties as P. Kasvis.Additionally, S.E.Loiselle entered and audited anthropometric and DXA data and was involved in the entry and dietary analysis of collected 24-hour recalls and food diaries.N. Kim was responsible for DXA and peripheral quantitative computed tomography scans and subsequent data entry.C. Vanstone was responsible for the coordination of the study and research unit and was responsible for blood draws, blood pressure and heart rate measures at each visit.Blood processing for analysis and storage was also handled by C. Vanstone.S. Agellon was responsible for training and overseeing Liaison measurements performed by P. Kasvis.T. Hazell was involved in study design and the creation of questionnaires.DXA, pQCT and force plate measures were also performed by T. Hazell.Baseline biochemistry of 25(OH)D, parathyroid hormone and osteocalcin were also part of his duties.H. Plourde contributed to study design.C. Rodd contributed to study design and provided medical assistance to participants in need of interventions.H. Weiler is the primary investigator of the MYLIFE study, was responsible for the conception and design of the project and is P. Kasvis' supervisor.

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