Introduction

Childhood overweight continues to be a major challenge worldwide, associated with serious health consequences and psycho-social outcomes (^{Lakshman, Elks, & Ong, 2012}; ^{Reilly et al., 2003}). Alarmingly, one out of four Spanish children is already overweight or obese by age five (^{Miqueleiz et al., 2014}). This prevalence is of considerable concern owing to the adverse consequences of childhood overweight and the fact that weight status at 5 years of age is a good indicator of the future health of a child (^{Gardner et al., 2009}). Furthermore, overweight during childhood tends to persist into adulthood (^{Freedman Mei, Srinivasan, Berenson, & Dietz, 2004}) with resultant long-term consequences that are difficult to treat successfully in the long term. Therefore, prevention of the onset of overweight is a public health priority and should be a primary target (^{Cominato et al., 2018}; ^{GordonLarsen, Adair, Nelson, & Popkin, 2004}). Indeed, the key to prevention is to examine and fully characterize the factors involved in the development of overweight.

Overweight is a multi-factorial condition influenced by diverse factors operating across the lifespan: genetic, neuroendocrine, metabolic, psychological, environmental and socio-cultural. To develop evidence-based policy and program decision-making, it is crucial to identify the risk factors associated with pediatric overweight. In a recent systematic review of thirty prospective studies from developed countries, several significant early-life risk factors were identified for childhood overweight: maternal prepregnancy overweight, high infant birth-weight, early infant rapid weight gain and maternal smoking during pregnancy (Weng, Redsell, Swift, Yang, & Glazebrook, 2012). However, research has mainly focused on school-aged children and adolescents, although the preschool years are a critical period for obesity prevention (^{Baker, Olsen, & Sørensen, 2007}). Given the high prevalence of overweight across Southern Europe (^{van Stralen et al., 2012}), research is particularly needed on preschoolers in these countries, including Spain.

This study explores the main risk factors for the development of childhood overweight in a large community sample of Spanish preschoolers longitudinally assessed from ages 3 to 5 years-old. The set of potential risk factors includes variables of the main areas associated with overweight during childhood and adolescence, including family structure, pregnancy, birth, postnatal period, medical history, school and neighborhood.

Method

Results

Discussion

To the best of our knowledge, this is the first community-based study to examine a variety of risk factors for overweight in a sample of Spanish preschoolers.

Socioeconomic status was independently associated with overweight, and this pattern remained for both genders over the 3-year assessment. As in other studies (^{Stamatakis et al., 2010}), we observed a gradient whereby children of socioeconomically disadvantaged families were more likely to be overweight. That this is seen in preschool years suggests that differences in adiposity by socioeconomic status may emerge early in life.

The stepwise regression analysis carried out revealed several risk factors for overweight. Among them, infant birth weight was the most relevant predictor for overweight. Therefore, the risk of overweight escalates with increasing birth weight in both genders. Several studies have demonstrated an association between high birth weight and overweight in children (^{Mitchell et al., 2016}; ^{Weng et al., 2012};), underlining the importance of weight monitoring from postpartum and routine screening for overweight in children who had high birth weight as a means of preventing adverse health outcomes.

In this study, American-Hispanic children had tripled the prevalence of overweight found in Caucasian children and being an ethnic minority was associated with overweight at age 4 and 5. Ethnic minorities have been shown to be more prone to overweight in many European countries (^{Veldhuis et al., 2013}). Members of minority ethnic groups often have lower socioeconomic status, which is in turn associated with a greater risk of obesity in children. Inequities in a range of factors (such us income, stable and affordable housing and access to quality education), disparate access to affordable, healthy food or safe places to be physically active and the fact that less nutritious, calorie-dense foods are often less expensive than healthier foods contribute to higher rates of obesity in ethnic minorities. Addressing these disparities requires making healthier choices easier in children's and families' daily lives by removing obstacles that make healthy, affordable food less accessible, and at the same time ensuring communities have more safe and accessible places for kids to be physically active. However, it is important to mention that in this study all the analyses were controlled for socioeconomic status, highlighting the fact that the reasons for the differences in prevalence of childhood obesity among different ethnic groups are complex, likely involving genetics, physiology, culture and environment.

Lower scores in the CBQ attention focusing scale were associated with overweight at age 3 supporting studies linking attention deficit with excess weight in childhood. ^{Faith and Hittner (2010)} found that among boys, poorer attention span at the age of 1 year-old predicted greater weight gain at 6 years of age. Results obtained in a previous study using the same sample showed that ADHD symptoms were associated with overweight as early as the preschool years (^{Perez-Bonaventura, Granero, & Ezpeleta, 2015}). It might be that reduced attention span interferes in the development of self-regulatory eating and satiety recognition, leaving the child relatively inattentive to hunger and satiety cues. Interestingly, in our study, the scale attention focusing was only associated negatively with overweight at age 3, but not at age 4 and 5, suggesting that attention focusing is only one of the clinical features of ADHD and that boarder tests are needed to provide more insight into the relationship between ADHD and overweight.

Maternal smoking during pregnancy was associated with overweight at age 3. The relationship between maternal smoking and childhood obesity has been described as catch-up growth following low birth weight caused by smoking during pregnancy or the poorer eating habits of smoking mothers (^{Hui, Nelson, Yu, Li, & Fok, 2003}).

In line with other reports (^{Kuhle, Allen, & Veugelers, 2010}), excess television screen time, before the age of 3 years-old was associated with overweight at 4 years-old. Various mechanisms may explain this association; prolonged periods of inactivity, the opportunity to eat snacks, a decline in energy expenditure, and the influence of commercials on food choices and nutrition. Consequently the American Academy of Pediatrics (^{American Academy of Pediatrics, 2013}) has recommended for over a decade that parents limit television viewing to no more than 2 h per day.

This study showed that when a child presented symptoms of DSM-IV feeding disorder of infancy before the age of 3 (a child's refusal to eat certain food groups, textures, solids or liquids or refusal to accept new foods), there was a negative association with overweight.

Some aspects of early parenting style were associated with later excess of body weight such as inconsistent discipline, fewer rules and corporal punishment. ^{Whitaker, Philips, Orzol, and Burdette (2007)} reported that the odds of obesity for 3-year-old children were 50 % higher for those who experienced neglect in the previous year. In another study, those adults who reported experiencing harsh physical punishment during childhood had a higher likelihood of obesity (^{Afifi, Mota, MacMillan, & Sareen, 2013}). Moreover, lack of effective rules in families with obese children often interferes with the development of regulated eating patterns.

Among fathers, some psychological symptoms scales, such as externalizing symptoms and total number of symptoms, were associated with the child's weight. Adults with binge eating disorders describe their childhood environment and the parenting they received more negatively than healthy controls (^{Hodges, Cochrane, & Brewerton, 1998}). During childhood, they might have used eating as a strategy to cope with negative feelings. The effect of father's psychopathology on the child's weight may also be mediated through parenting. Knowledge of the mechanisms involved may help us to modify dysfunctional associations and improve the child's adjustment.

On a community level, the only variable that showed a relationship with weight status was living near a traffic dense route (< 300 m), which was only associated with zBMI at age 3. Growing evidence suggests air pollution as a risk factor for the development of obesity and overweight. Several epidemiological studies have reported an association between various ambient and indoor air pollutants and obesity (^{Limaye & Salvi, 2014}). Evidence-based research to link children's health, physiology, and behavior to atmospheric extremes is an important area of future research.

This study indicates that greater understanding of the risk factors identified might help with early prevention and intervention programs. The fact that we included a community population of young children within a small age range specific to preschool age group adds to existing knowledge.

The main study strengths are the longitudinal assessment of risk factors of overweight in preschool children, the inclusion of a large set of potential predictors including individual, family and community level factors and a large community sample (from the general population).

Some of the study's limitations should also be considered when interpreting the results. Had the data been available, additional relevant risk factors potentially contributing to weight gain in childhood could have been explored, such as, parental overweight, physical activity or energy expenditure. However, this study is the first to examine a broad variety of risk factors for overweight in Spanish preschoolers. Future studies should explore more detailed information on these risk factors. Another study limitation is that measurements of the children's weight and height were taken from medical records, although routine weight measurements have been found to be highly accurate, which supports their usefulness in both clinical practice and research (^{Howe, Tilling, & Lawlor, 2009}). Another limitation is that few families of low socioeconomic status participated in our study, possibly families of higher socioeconomic status are overrepresented in the study. Finally, some scales of the Spanish version of the CBQ had low alphas in the current sample, although this must be interpreted with caution due to the small number of items and the CBQ scale Attention Focusing (which was the only scale that was statistically significant) had an alpha value of α = .69 (almost .70 which is considered acceptable for a measurement scale).

The preschool years are a period of rapid growth and habit formation. Knowledge of the age at which the association between early specific risk factors and weight status becomes significant can provide avenues for early interventions.