Cohort Profile: The transition from childhood to adolescence in European children–how I.Family extends the IDEFICS cohort

Worldwide, nutrition-related diseases have become a major health concern. The most apparent consequence of unhealthy diets and lack of physical activity is excess body weight and resulting cardiovascular and metabolic sequelae.1 Many of these unfavourable health outcomes have developmental origins and track into adulthood2 with unacceptable human, social and economic costs.1 Social inequalities create unequal pressures and opportunities, relating to a range of environmental, social and economic factors,3 some of which impinge on diet, addictive behaviours, physical activity, sedentariness, media exposure and parenting.4 Factors conducive to ill health cluster in certain segments of the society, e.g. those from lower socioeconomic position, those with poor mental health or poor cognitive abilities, or who are immigrants.5 These inequalities call for efforts of European policy to increase social cohesion and quality of life and to encourage sustainable healthy lifestyles for all citizens, especially children.6 There is an apparent lack of longitudinal studies that allow the investigation of biological markers and lifestyle behaviours combined with social, cultural and environmental factors and related to health and development across the early life course. There are some national birth and/ or child cohorts like ALSPAC7 in the UK, MoBa8 in Norway, the Aarhus Birth Cohort9 in Denmark, the Generation R Study10 in The Netherlands or KIGGS11 in Germany that may serve this aim. But to our knowledge there is no pan-European population-based cohort of children representing diverse European lifestyles and considering multiple exposures and outcomes. This gap is filled by the IDEFICS cohort. The first two examination waves of this cohort are from the IDEFICS (Identiflcation and prevention of dietary and lifestyle-induced health effects in children and infants) study. Dietary, behavioural and socioeconomic factors have been investigated in relation to non-communicable chronic diseases and disorders in this large sample of European children by means of a prospective cohort study, focusing on overweight and obesity.12 An extensive phenotyping in combination with genetic analyses (Figure 1, left section) allows us to disentangle the contributions of factors acting at various levels. Details of the objectives, the IDEFICS study design and the instruments foreseen for the examination waves have already been published before the study had started.13,14 Some study procedures had to be modified after completion of the pre-tests.15 The observational design of the IDEFICS study was complemented by a setting-based community-oriented intervention programme for primary prevention of obesity. It aimed to examine the feasibility, effectiveness and sustainability of a coherent set of intervention modules addressing diet, physical activity and stress.16 Longitudinal design of the IDEFICS study, its concatenation with the I.Family study and overview of all examination modules. CAQDA, Computer-Assisted Qualitative Data Analysis; FFQ, Food Frequency Questionnaire; T0, baseline survey; T1, first follow-up examination; T2, mailed survey; T3, second follow-up examination. An extension and a further follow-up (third examination wave) of the IDEFICS children’s cohort was performed in the framework of the EC FP7 project, I.Family, to create a longitudinal database of children and their families17 (Figure 1, right section). Given the limited knowledge about familial resemblance of dietary patterns rather than single food groups such as fruits and vegetables or fast food,18–21 I.Family investigates associations between children’s and parents’ dietary patterns and whether the family food environment mediates these associations, something that no other large study has done. The cohort provides repeated measurements of social and behavioural factors, individual characteristics and medical parameters to be related to health behaviours and health outcomes observed in later years in the same individuals. The data on health and nutrition are complemented with data on parenting style and family life, by including siblings and parents. It will be possible to determine the influence of families on children’s behaviour and to study the complex and dynamic transition from childhood to adolescence, when behaviours begin to be influenced by other social and environmental factors than familial habits. Our research is conceptually based on the human ecological model.22 It provides an excellent framework for cross-cultural research, taking advantage of the diversity of genetic structures, physical environments, dietary habits, climate zones and socio-cultural contexts across Europe. Figure 1 and Figure 2 illustrate the evolution of the study cohort. The baseline examination (T0) between September 2007 and June 2008 included 16 228 children aged 2 to 9.9 years from eight European countries: Belgium, Cyprus, Estonia, Germany, Hungary, Italy, Spain and Sweden. In each country we selected two or more communities whose socio-demographic profile and infrastructure were similar and typical for their region. Within each community all children attending kindergartens and primary schools were eligible. Parents were approached via these settings and asked for consent to examine their children. The main characteristics of the cohort at baseline have been described.23 Historical records of routine child visits were collected to extend the observation period from birth to enrolment into the study. We also collected maternity cards to obtain data on fetal growth. In Sweden, health archives were retrieved from non-participating as well as participating children in the study communities, yielding no evidence of under-representation of children with overweight at baseline; however, some biases with regard to familial socioeconomic factors were observed.24 Flow chart of the baseline recruitment and subsequent follow-up examinations of the IDEFICS cohort and its extension by the I.Family studya T0, baseline survey; T1, first follow-up examination; T2, mailed survey; T3, second follow-up examination. aNot shown in the figure: process evaluation based on questionnaire mailed at T2 and selection of contrasting groups after T3 stage 1. All applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during this research. Approval by the appropriate ethics committees was obtained by each of the centres doing the fieldwork. Study children did not undergo any procedure before both they and their parents had given consent for examinations, collection of samples, subsequent analysis and storage of personal data and collected samples. Study subjects and their parents could consent to single components of the study while abstaining from others. Two years after baseline, 11 041 (68%) of all children participated in the first follow-up examination (T1) (Figure 2). Drop-outs between examinations were more likely to be overweight, to report low well-being scores and to come from less educated or single parent families. Moreover, attrition was positively associated with a high degree of item nonresponse at T0.25 Due to the setting-based recruitment, participation was offered to other schools and classmates of study participants. Thus 2555 children were newly recruited at T1. The same examination modules were deployed at T0 and T1. In addition, we assessed the penetration of the intervention messages by a mail survey (T2). As the starting point of the I.Family study, another follow-up examination (T3) was conducted in 2013-2014, when the age range of index children, i.e. of children who had already participated at T0 or T1, was between 5 and 17 years. The mean age [standard deviation (SD)] was 6.0 (1.8) years at baseline, 7.9 (1.9) years at T1 and 10.9 (2.9) years at T3 with a nearly equal proportion of boys and girls. Since we aimed to investigate entire families, we invited all siblings in the same age range as the index children. The role of familial characteristics, family structure and family life in relation to the children’s development is a major focus of I.Family, and we thus strived for at least one parent of each index child to participate and to provide information on their household. In this way, 6167 families with on average 2 children and 4.1 members (including parents) per family provided the necessary data. Figure 3 gives an overview of the sequence and timing of data collections. T0 denotes the baseline survey, i.e. the establishment of the cohort. All examinations performed at T0 were repeated at T1, both in index children volunteering to participate in the follow-up and in children newly recruited at T1. At T2 we only collected information on exposure to the intervention with a self-completion questionnaire mailed to the parents of index children in the intervention regions. At T3 we invited all children participating at T0 or T1 as well as their siblings and parents. The examination programme of this most recent follow-up covered the majority of the modules employed at T0 and T1. New modules on family life, peers and kinship structure were included at T3 (Table 1). The design of the study allowed for an additional, more extensive examination of ‘contrasting groups’ (see below). Overview of measurements and variables collected at baseline examination (T0) and at two follow-up examinations (T1 and T3) in children and their parents At T0 and T1 only sleep duration. Self-report of children ≥ 8 years at T3. Only newly recruited subjects. If venepuncture was refused, children were asked for capillary blood (only T0 - T1). Parents only at T3 and only optional. Only in subsamples of school-aged children. Only in three selected geographical regions. Overview of measurements and variables collected at baseline examination (T0) and at two follow-up examinations (T1 and T3) in children and their parents At T0 and T1 only sleep duration. Self-report of children ≥ 8 years at T3. Only newly recruited subjects. If venepuncture was refused, children were asked for capillary blood (only T0 - T1). Parents only at T3 and only optional. Only in subsamples of school-aged children. Only in three selected geographical regions. Timeline of the follow-up examinations of the IDEFICS cohort and its extension by the I.Family study T0, baseline survey; T1, first follow-up examination; T2, mailed survey; T3, second follow-up examination; CG, contrasting groups (extended examination in subgroups of the cohort). The average observation period for children included in any of the follow-up examinations is 3.9 years (SD = 1.9), with the following distribution: 1 to <2 years: 1901 children; 2 to <3 years: 4068 children; 3 to <4 years: 670 children; 4 to <5 years: 413 children; 5 to <6 years: 3300 children; 6+ years: 2697 children. Overall, the cohort has accumulated 50 940 person-years. Table 1 gives an overview of the questionnaires and other examination modules employed at the various stages of recruitment and follow-up of the cohort. In the IDEFICS study we measured weight status and related health outcomes such as blood pressure and insulin resistance, proximal behavioural determinants such as physical activity, sedentary behaviours, sleep and diet and distal determinants such as social factors, electronic media exposure and the physical environment. Preference was given to established and/or validated instruments suitable for population-based studies in children. All instruments and measurement procedures were pre-tested and adapted for each survey centre. We also assessed the reliability of instruments and examinations. Results of pre-tests and reliability studies were published.26 The special focus of the follow-up study I.Family required the development of new instruments, e.g. a kinship questionnaire, and the use of additional measurement tools such as neuropsychological tests on decision making, set shifting capacity and inhibitory capacity as well as pictograms to assess maturation stages according to Tanner and a web-based 24-h dietary recall (24-HDR). Whereas the medical history, to be completed by parents for both their children and for themselves was obtained by interview, paper-and-pencil versions of the general questionnaire and the food frequency questionnaire were self-completed by almost all parents for their children below the age of 12 at all three time points. At T3, when the questionnaire on dietary habits and food consumption frequency was combined with the general questionnaire, teens completed a tailored version of it on a tablet PC and at least one parent completed it also for him/herself in 90% of the families. At T0 and T1 parents were asked to complete at least one computer-based 24-HDR for their children at the study centre, with support from the study personnel. A web-based version was offered to all participants aged ≥ 8 years at T3 with the recommendation to complete the first one at the examination centre and another two 24-HDRs on non-consecutive days including one weekend day during the next 2 weeks. Parents were asked to assist smaller children (< 8 years old) in completing their 24-HDR. A second series of three 24-HDRs was requested 6 months after the T3 examination. IDEFICS instruments designed for small children and their proxies were adapted for use in adolescents and adults in order to yield comparable data for longitudinal analyses of repeated measurements. All instruments used in the second follow-up are listed in Supplementary Table 1, available as Supplementary data at IJE online. Several specific tests and measurements were only performed in subgroups. At T0 and T1 approximately half of the children were asked to wear a uniaxial accelerometer (Actigraph) for 3 days and either a uniaxial or a three-axial accelerometer for a full week at T3. At this time, consistent with the I.Family focus, parents were also asked to wear an accelerometer. Most physical fitness tests were restricted to T0 and T1. Percentages of various modules completed by study participants differ because selected modules were only offered to subgroups, and subjects could opt out of single examination modules (Table 2). Number of subjects who participated in the various examination modules at the three waves n.a., not available. All physical examination modules were optional for parents (adults). Optional examination module. Optional at T3. Capillary blood only asked from children who refused venepuncture. Collection restricted to children for whom was from of children provided at least one only offered to subgroups. restricted to Number of subjects who participated in the various examination modules at the three waves n.a., not available. All physical examination modules were optional for parents (adults). Optional examination module. Optional at T3. Capillary blood only asked from children who refused venepuncture. Collection restricted to children for whom was from of children provided at least one only offered to subgroups. restricted to 1 after completion of T3 examinations of contrasting groups as in Figure 1 and Figure i.e. subsamples of children with weight were conducted stage 2). groups were based on weight status and in body index as children who i.e. who a between and at baseline and follow-up and did not more than in per children who overweight or i.e. who had a of more than at baseline and and did not more than in per and children with weight were those who with a at baseline and who more than in per during the follow-up of contrasting groups will the of determinants as well as of weight The additional examinations in these subgroups included measurements of sleep quality and tests in both children and their parents. on and were performed in a of about of school-aged children at T0 and T1. Preference tests were repeated in and combined with In a of a children, were collected at T1, at T3 and in to the in weight and overweight children In selected the measurement of physical activity was combined with and information on the physical environment obtained from information was collected to determine the influence of the environment on physical activity and health outcomes. The examination of contrasting groups also included of the in three to assess by food in a smaller of and overweight children and their parents. was by of visits during the data and of biological samples. A of data patterns in and and low in were associated with lower of and less weight A cluster analysis to dietary patterns that children from a lower socioeconomic had dietary a excess was associated with In a of primary children, for was associated with The proportion of children who physical activity of of physical activity per day from to in and from to in An additional per day of was related to an assess the of the environment on in children, we a to a index from on information analyses a on the of in the study In and of and combined effects on sleep between with in Europe. A between sleep and overweight was observed this was in children than in The between sleep and is by the between sleep and body may of this in at the of the of children to time (< who sedentary were at of high blood during a in the children’s and for more than 1 were all associated with exposure to was associated with a for and with and a consumption of for on was associated with and a for to these was related to their for well-being was by exposure and PC use as by and in and family in boys and The combined of in from more than in to less than in Europe. Overall, the was in as with boys and a with and and markers as well as blood pressure and measurements were used to and based on the for and and to a metabolic for All were and have already major It is to be that they will have In order to of were used to study the between body index during and later metabolic We observed that at of during to early childhood months to <6 and later childhood 6 as well as were associated with the at from especially in the time of months to 6 later metabolic in children. We the between the and body and a a increase of body and and a nearly of during were observed A A multiple that children the were more by a social environment the development of than children the or In a children with consumption of in blood with those with or high In children with consumption of lower with those with low or of and in may serve as of consumption of and A of children the has these data have become available for the full of will be genetic scores for on or dietary The cohort will also to and The setting-based IDEFICS intervention was the intervention as a physical activity, dietary behaviour and modules at the community the and the family behavioural and process assessed the and the sustainability of this intervention according to the IDEFICS intervention was according to only effects were observed after 2 years of effects after 2 years were in the of children who were already overweight at Moreover, 6 years after the intervention we observed that parents and children who were to the IDEFICS intervention had lower to than of this study and repeated phenotyping of participants in this of of children from diverse in the longitudinal across the developmental and the of familial The in all that is by a quality and data of measurements across study The study questionnaires with and examinations and in a are used for the of the genetic profile as well as parameters related to and other health outcomes. In the recent parents and newly recruited siblings also this to allow for the investigation of the role of genetic factors and the environment on children’s with the collection of maternity cards and records of routine child these longitudinal data allow for a that across developmental The of social that become as children is a further examinations and the of the physical and social environment in are because of their There are also some The the to opt out of single examination and some modules were only in subgroups. This to a of subjects per examination and small for a given The study from the diversity of lifestyles and across it was not to a for each the primary of this study, i.e. the of factors behaviours in children and adolescents and the investigation of the of various factors in their relation to health not be by selection may be The IDEFICS cohort has that it a to early life factors health outcomes that track into and that are already in childhood and the time from early childhood adolescence, it allows the investigation of developmental such as the from into early to and from childhood into in an early The of parents and siblings in the study and the of us to the investigation of individual children the investigation of our study subjects as members of families and other social in a measurements in the same allow the of developmental The of parameters the of measurements and the collection of allow for a The longitudinal of the IDEFICS cohort allows of factors for metabolic disorders and other health outcomes. This will support the of and of scores for or metabolic for and the that approximately half of the children in the intervention allows for the of possible intervention Due to the prospective of this cohort study, the full of study data is out and use of data a between our study and on a the study The IDEFICS cohort profile in a The IDEFICS cohort the of socioeconomic and environmental factors on non-communicable chronic diseases in a large diverse sample of European children during developmental of and of investigation of the children as members of social in a At baseline 16 228 children aged years from Belgium, Cyprus, Estonia, Germany, Hungary, Italy, Spain and were were after 2 and 6 with more than 12 children participated in at least two examination index children and newly recruited siblings participated in the most recent Parents and other lifestyle data for their small children and families and were collected from of children included blood physical from and markers in blood and The neuropsychological characteristics and other of children’s food were in subgroups. of data a between the study and on a Supplementary data are available at IJE online. The baseline data collection and the first follow-up as of the IDEFICS Study were by the European the The most recent follow-up was conducted in the framework of the I.Family study which was by the European the were by all participating is by the of the support of the of and the and for support of the IDEFICS and I.Family of We are for the support of and The to the IDEFICS children and their parents for participating in this extensive examination. We also our to the entire study i.e. our study and intervention data and We are to our of Food who was one of the main of the I.Family a in the development of our research tools and the IDEFICS in June