Jenny Peplies

Assessment of diet, physical activity and biological, social and environmental factors in a multi-centre European project on diet- and lifestyle-related disorders in children (IDEFICS)

Obesity is a major public health problem in developed countries. We present a European project, called Identification and Prevention of Dietary and Lifestyle-induced Health Effects in Children and Infants (IDEFICS), that focuses on diet- and lifestyle-related diseases in children. This paper outlines methodological aspects and means of quality control in IDEFICS. IDEFICS will use a multicentre survey design of a population-based cohort of about 17,000 2- to 10-year-old children in nine European countries (Belgium, Cyprus, Estonia, Germany, Greece, Hungary, Italy, Spain and Sweden). The project will investigate the impact of dietary factors such as food intake and food preferences, lifestyle factors such as physical activity, psychosocial factors and genetic factors on the development of obesity and other selected diet- and lifestyle-related disorders. An intervention study will be set up in pre-school and primary school settings in eight of the survey centres. Standardised survey instruments will be designed during the first phase of the project and applied in the surveys by all centres. Standard operation procedures (SOPs) will be developed, as well as a plan for training the personnel involved in the surveys. These activities will be accompanied by a quality control strategy that will encompass the evaluation of process and result quality throughout the project. IDEFICS will develop comparable Europe-wide health indicators and instruments for data collection among young children. Establishment of a new European cohort within IDEFICS will provide a unique opportunity to document the development of the obesity epidemic in the current generation of young Europeans and investigate the impact of primary prevention in European children populations.

Design and results of the pretest of the IDEFICS study

Background:During the preparatory phase of the baseline survey of the IDEFICS (Identification and prevention of dietary- and lifestyle-induced health effects in children and infants) study, standardised survey procedures including instruments, examinations, methods, biological sampling and software tools were developed and pretested for their feasibility, robustness and acceptability.Methods:A pretest was conducted of full survey procedures in 119 children aged 2–9 years in nine European survey centres (N per centre=4–27, mean 13.22). Novel techniques such as ultrasound measurements to assess subcutaneous fat and bone health, heart rate monitors combined with accelerometers and sensory taste perception tests were used.Results:Biological sampling, physical examinations, sensory taste perception tests, parental questionnaire and medical interview required only minor amendments, whereas physical fitness tests required major adaptations. Callipers for skinfold measurements were favoured over ultrasonography, as the latter showed only a low-to-modest agreement with calliper measurements (correlation coefficients of r=−0.22 and r=0.67 for all children). The combination of accelerometers with heart rate monitors was feasible in school children only. Implementation of the computer-based 24-h dietary recall required a complex and intensive developmental stage. It was combined with the assessment of school meals, which was changed after the pretest from portion weighing to the more feasible observation of the consumed portion size per child. The inclusion of heel ultrasonometry as an indicator of bone stiffness was the most important amendment after the pretest.Discussion:Feasibility and acceptability of all procedures had to be balanced against their scientific value. Extensive pretesting, training and subsequent refinement of the methods were necessary to assess the feasibility of all instruments and procedures in routine fieldwork and to exchange or modify procedures that would otherwise give invalid or misleading results.

Early Life Course Risk Factors for Childhood Obesity: The IDEFICS Case-Control Study

Background The early life course is assumed to be a critical phase for childhood obesity; however the significance of single factors and their interplay is not well studied in childhood populations. Objectives The investigation of pre-, peri- and postpartum risk factors on the risk of obesity at age 2 to 9. Methods A case-control study with 1,024 1∶1-matched case-control pairs was nested in the baseline survey (09/2007–05/2008) of the IDEFICS study, a population-based intervention study on childhood obesity carried out in 8 European countries in pre- and primary school settings. Conditional logistic regression was used for identification of risk factors. Results For many of the investigated risk factors, we found a raw effect in our study. In multivariate models, we could establish an effect for gestational weight gain (adjusted OR = 1.02; 95%CI 1.00–1.04), smoking during pregnancy (adjusted OR = 1.48; 95%CI 1.08–2.01), Caesarian section (adjusted OR = 1.38; 95%CI 1.10–1.74), and breastfeeding 4 to 11 months (adjusted OR = 0.77; 95%CI 0.62–0.96). Birth weight was related to lean mass rather than to fat mass, the effect of smoking was found only in boys, but not in girls. After additional adjustment for parental BMI and parental educational status, only gestational weight gain remained statistically significant. Both, maternal as well as paternal BMI were the strongest risk factors in our study, and they confounded several of the investigated associations. Conclusions Key risk factors of childhood obesity in our study are parental BMI and gestational weight gain; consequently prevention approaches should target not only children but also adults. The monitoring of gestational weight seems to be of particular importance for early prevention of childhood obesity.

DNA yield and quality of saliva samples and suitability for large scale epidemiological studies in children

Objective:To evaluate two saliva collection methods for DNA yield and quality as applied to a large, integrated, multicentre, European project involving the collection of biological material from children.Design:Cross-sectional multicentre comparative study in young children.Methods:Saliva samples were collected from 14 019 children aged 2–9 years from eight European countries participating in the IDEFICS (Identification and prevention of dietary- and lifestyle-induced health effects in children and infants) study. This involved either the collection of 2 ml of saliva from children who were able to spit, or using a sponge to collect whole saliva and buccal mucosal cells from the inside of the mouth of younger children unable to spit. Samples were assembled centrally in each participating centre and subsequently despatched for DNA extraction and biobanking to the University of Glasgow. A subgroup of 4678 samples (∼33% of sampled individuals) were chosen for DNA extraction before genotyping.Results:The whole-saliva collection method resulted in a higher DNA yield than the sponge collection method (mean±s.d.; saliva: 20.95±2.35 μg, sponge: 9.13±2.25 μg; P<0.001). DNA quality as measured by A 260/A 280 was similar for the two collection methods. A minimum genotype calling success rate of 95% showed that both methods provide good-quality DNA for genotyping using TaqMan allelic discrimination assays.Conclusions:Our results showed higher DNA yield from the whole-saliva collection method compared with the assisted sponge collection. However, both collection methods provided DNA of sufficient quantity and quality for large-scale genetic epidemiological studies.

High‐sensitivity C‐reactive Protein is a Predictive Factor of Adiposity in Children: Results of the Identification and prevention of Dietary‐ and lifestyle‐induced health Effects in Children and InfantS (IDEFICS) Study

Background Whereas cross‐sectional studies have shown that obesity is associated with increased C‐reactive protein (CRP) levels in children, little is known about the impact of low‐grade inflammation on body mass changes during growth. Methods and Results We assessed cross‐sectionally and longitudinally the association of high‐sensitivity (hs)‐CRP levels with overweight/obesity and related cardiometabolic risk factors in the Identification and prevention of Dietary‐ and lifestyle‐induced health Effects in Children and InfantS (IDEFICS) cohort. 16 224 children from 8 European countries (2 to 9 years) were recruited during the baseline survey (T0). After the exclusion of 7187 children because of missing hs‐CRP measurements and 2421 because of drug use during the previous week, the analysis was performed on 6616 children (Boys=3347; Girls=3269; age=6.3±1.7 years). Of them, 4110 were reexamined 2 years later (T1). Anthropometric variables, blood pressure, hs‐CRP, blood lipids, glucose and insulin were measured. The population at T0 was divided into 3 categories, according to the baseline hs‐CRP levels. Higher hs‐CRP levels were associated with significantly higher prevalence of overweight/obesity, body mass index (BMI) z‐score and central adiposity indices (P values all <0.0001), and with higher blood pressure and lower HDL‐cholesterol levels. Over the 2‐year follow‐up, higher baseline hs‐CRP levels were associated with a significant increase in BMI z‐score (P<0.001) and significantly higher risk of incident overweight/obesity. Conclusions Higher hs‐CRP levels are associated to higher body mass and overweight/obesity risk in a large population of European children. Children with higher baseline levels of hs‐CRP had a greater increase in BMI z‐score and central adiposity over time and were at higher risk of developing overweight/obesity during growth.

Influence of sample collection and preanalytical sample processing on the analyses of biological markers in the European multicentre study IDEFICS

Objective:To evaluate the influence of a standardised sampling protocol and process quality across the different IDEFICS (Identification and prevention of dietary- and lifestyle-induced health effects in children and infants) centres on the results of the biochemical measurements.Design:Baseline survey within the community-based intervention study.Subjects:A total of 16 224 children, aged 2–8 years, enrolled in the IDEFICS baseline survey in 8 European countries. Venous or capillary blood samples were collected from 12 430 children, urine samples from 13 890 children and saliva samples from 14 019 children.Methods:A set of quality indicators was recorded for the biological blood, urine and saliva samples collected during the IDEFICS study. Results of blood and urine measurements were analysed and stratified by selected quality indicators.Results:Concentrations of biological markers in blood and urine measured during the IDEFICS baseline survey are associated with several quality indicators assessed in this study. Between-country variations of these biomarkers are described. It was confirmed that fasting has a big influence on the concentration of certain biomarkers. Biomarkers in morning urine samples may be erroneous if the study subjects void during the night or if samples are not taken from the very first morning urine.Conclusions:The analysed data underline that a standardised sampling protocol is of major importance, especially in multicentre studies, but non-compliance is ever present in spite of well-defined standard operation procedures. Deviations from the protocol should therefore always be documented to avoid error pertaining to the concentration of biological markers.

Percentiles of fasting serum insulin, glucose, HbA1c and HOMA-IR in pre-pubertal normal weight European children from the IDEFICS cohort

Objectives:The aim of this study is to present age- and sex-specific reference values of insulin, glucose, glycosylated haemoglobin (HbA1c) and the homeostasis model assessment to quantify insulin resistance (HOMA-IR) for pre-pubertal children.Methods:The reference population consists of 7074 normal weight 3- to 10.9-year-old pre-pubertal children from eight European countries who participated in at least one wave of the IDEFICS (‘identification and prevention of dietary- and lifestyle-induced health effects in children and infants’) surveys (2007–2010) and for whom standardised laboratory measurements were obtained. Percentile curves of insulin (measured by an electrochemiluminescence immunoassay), glucose, HbA1c and HOMA-IR were calculated as a function of age stratified by sex using the general additive model for location scale and shape (GAMLSS) method.Results:Levels of insulin, fasting glucose and HOMA-IR continuously show an increasing trend with age, whereas HbA1c shows an upward trend only beyond the age of 8 years. Insulin and HOMA-IR values are higher in girls of all age groups, whereas glucose values are slightly higher in boys. Median serum levels of insulin range from 17.4 and 13.2 pmol l−1 in 3–<3.5-year-old girls and boys, respectively, to 53.5 and 43.0 pmol l−1 in 10.5–<11-year-old girls and boys. Median values of glucose are 4.3 and 4.5 mmol l−1 in the youngest age group and 49.3 and 50.6 mmol l−1 in the oldest girls and boys. For HOMA-IR, median values range from 0.5 and 0.4 in 3–<3.5-year-old girls and boys to 1.7 and 1.4 in 10.5–<11-year-old girls and boys, respectively.Conclusions:Our study provides the first standardised reference values for an international European children’s population and provides the, up to now, largest data set of healthy pre-pubertal children to model reference percentiles for markers of insulin resistance. Our cohort shows higher values of Hb1Ac as compared with a single Swedish study while our percentiles for the other glucose metabolic markers are in good accordance with previous studies.

Food consumption and cardiovascular risk factors in European children: the IDEFICS study.

Few studies addressing the relationship between food consumption and cardiovascular disease or metabolic risk have been conducted in children. Previous findings have indicated greater metabolic risk in children with high intakes of solid hydrogenated fat and white bread, and low consumption of fruits, vegetables and dairy products.

Blood lipids among young children in Europe: results from the European IDEFICS study.

Background:Measurement of cholesterol and triglyceride (TG) fractions in blood has become standard practice in the early detection of atherosclerotic disease pathways. Considerable attention is given nowadays to the presence of these risk factors in children and to start preventive campaigns early in life. In this context, it is imperative to have valid comparative frameworks for interpretation of lipid levels. The aim of this study is to present sex- and age-specific reference values on blood lipid levels in European children aged 2.0–10.9 years.Methods:Fasting blood was obtained via either venipuncture or capillary sampling. In 13 579 European non-obese children (50.3% boys), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), total cholesterol (TC), TG and TC/HDL-C ratio levels were measured with a point-of-care analyser (Cholestech). Sex- and age-specific reference values were computed with the GAMLSS method with the statistical software R.Results:Reference curves and 1st, 3rd, 10th, 25th, 50th, 75th, 90th, 97th and 99th percentile values are presented. HDL-C showed a positive trend with age, from 2 years onwards, but was relatively stable above the age of 7. For LDL-C and TC, linear but small age-related trends were seen. The TC/HDL-C values showed a gradual negative trend from the age of 2 up to 6 and were relatively stable afterwards. For TG, no age trend was found (P=0.285). Boys had higher mean HDL-C values than girls (1.414 vs 1.368 mmol l−1), and lower TC, LDL-C, TC/HDL-C and TG values (3.981 vs 4.087 mmol l−1; 2.297 vs 2.435 mmol l−1; 2.84 vs 3.01mmol l−1;  and 0.509 vs 0.542 mmol l−1, respectively).Conclusions:These new and recent references could serve as a European orientation of blood lipid values in children in the context of standard medical practice and for the purpose of public health screening.

Quality management for the collection of biological samples in multicentre studies.

Large scale international multicentre studies require sophisticated quality management for the collection, processing and logistics of biological samples to ensure a maximum degree of standardisation across different environmental conditions and settings. This paper describes a quality management system for the collection of biological samples (QMS-BS) which was applied during IDEFICS, a large European multicentre study. The application was evaluated by several criteria like response rates for the different types of biological samples, measures of sample quality, compliance with the QMS-BS and efficiency of the document and sample control and of the quality assurance system. Response rates varied from 56.6% for venous blood collection to 90.1% for saliva collection. All sample types were associated with problems of sample quality (e.g. haemolysis of blood samples, lack of cooling for urine samples or desiccation of saliva samples). Overall compliance with the QMS-BS was good, with some exceptions mainly related to sample control. In conclusion the QMS-BS is a valuable tool for the management of biological sample collection in epidemiological multicentre studies.