The relationship between childcare and adiposity, body mass and obesity-related risk factors: protocol for a systematic review of longitudinal studies

High rates of childhood obesity are a worldwide concern [1]. Globally in 2010, approximately 6.7 % (43 million) of preschool-aged children were overweight or obese, and this prevalence is estimated to rise to 9.1 % by 2020 if current trends are maintained [2]. Obesity in childhood is associated with increased risk of both obesity in adulthood and a range of other conditions including low self-esteem, high blood pressure, insulin resistance, coronary heart disease and stroke [3‐8].

The early years (<6 years of age) have been repeatedly highlighted as a critical period for the development and prevention of obesity [6, 9‐11]. They are also an important period for the establishment of healthy habits, including healthy physical activity, dietary patterns and sleeping patterns [12‐14]—all of which can help protect against the development of obesity. Several individual (e.g. sex, dietary and activity behaviours), inter-personal (e.g. peer/sibling interactions, parent feeding practices) and environmental factors (e.g. neighbourhood safety, childcare) influence the development of childhood obesity [15]. As environmental factors affect large numbers of children, they represent potential targets for obesity prevention [16].

An increasing number of children now attend out-of-home childcare prior to 6 years of age, and many spend large proportions of their week days in such care [17, 18]. A recent report by the United Nations Children’s Emergency Fund shows that roughly 80 % of 3–6 year olds and 25 % of 0–3 year olds in developed countries spend time in some form of childcare [17]. As a result, childcare settings have been targeted for intervention efforts to prevent obesity [13, 19‐21].

A growing body of research suggests a positive association between childcare attendance and increased adiposity and risk of obesity in children [22‐29]. Geoffroy et al. found that Canadian children who attended centre-based childcare or were cared for by a relative between 1.5–4 years of age had higher odds of being overweight or obese at 4–10 years of age than those receiving parental care [22]. Similarly, Lin et al. found that informal childcare (e.g. by grandparents or domestic helpers) at ages 3 and 5 years was associated with increased risk for overweight and higher body mass index z-score at age 11, in comparison to those cared for by parents [27].

However, the relationship between non-parental childcare and future obesity in children is not consistent and may partly depend on specific aspects of the childcare received. These aspects include the type (i.e. informal versus formal care), duration (i.e. number of years spent in childcare), intensity (e.g. number of hours per week) and timing (i.e. age of onset of childcare) of care received. Additionally, relationships between non-parental childcare and future risk of obesity may vary according to different socio-demographic characteristics, such as child’s ethnicity and family’s socioeconomic position [30‐32]. For example, a study by Zahir et al. reported no association between attendance, age of entry and number of hours spent in non-parental childcare and risk of obesity at 4 years of age in a sample of Latino children [30]. Maher et al. found that Latino children in informal childcare or those who attended Head Start had lower risk of obesity at 4 years than those in parental care [31]. Conversely, non-Latino children in informal childcare had an increased risk of obesity [31]. A more recent study found that care by a non-relative was associated with increased body mass index percentile between 2–3 and 6–7 years for boys of all income levels, but in girls this association was only found for those in low-income households [32].

Furthermore, the pathways through which childcare experiences might affect obesity are poorly understood [33‐35]. Different types and characteristics of childcare settings may have different influences on development of obesity-related risk factors, such as physical activity, sedentary behaviour, sleep, diet and stress [19, 36‐43]. A recent systematic review identified some childcare staff behaviours (e.g. providing portable play equipment and playing with children) associated with increased physical activity in children in cross-sectional studies [44]. However, this was not seen across all studies investigating these behaviours, and there was a lack of evidence from longitudinal studies. Additionally, whilst some studies reported increased energy intake at childcare (e.g. average lunch intake in US 15–24 month olds: 281 kcal at home versus 332 kcal at childcare) [45], others have reported no difference in energy intake at home versus at childcare [29]. However, given evidence of associations between physical activity, sedentary behaviour, sleep, diet and stress with increased adiposity in early childhood [34, 46‐50], we hypothesise that these risk factors are possible pathways through which childcare may influence the development of obesity. To our knowledge, no previous systematic reviews have examined the associations between childcare and adiposity, obesity and obesity-related risk factors.