National, longitudinal NASCITA birth cohort study: prevalence of overweight at 12 months of age in children born healthy

Introduction

Childhood overweight and obesity represent an increasing public health issue that threatens future health and quality of life.1 Evidence suggests that there are early-life factors (eg, maternal body mass index (BMI), gestational weight gain, maternal smoking habits and infant feeding) associated with the development of obesity.2 3 Nutrition, in particular, plays an important role in growth and development and breast feeding (BF) is considered by the WHO the best method of nourishment for infants for its positive health effects on children and mothers in the short and long term.4

For these reasons, the WHO recommends that children should be exclusively breastfed for the first 6 months of life; afterward, they should begin eating safe and adequate complementary foods while continuing BF for up to 2 years and beyond.4

Several studies found an association between BF and a reduced risk of being overweight, even if results are not conclusive.5–7

Italy is one of the European countries with the greatest prevalence of childhood overweight and obesity, with a rate in the 8-year-old children of 42% and 21%, respectively.8 9 A North-South gradient was detected not only in Europe, but also within Italy.10 In particular, school-aged children living in the South of Italy have a twofold greater risk of overweight compared with children living in the North.10

However, there is scant information concerning the proportion of overweight Italian children at an early age.

In this context, this study aimed to describe the growth of newborns participating in the Italian national NASCITA (NAscere e creSCere in ITAlia) cohort in their first year of life, to estimate the BMI status and the prevalence of overweight at 12 months, and to identify potential factors associated with a greater likelihood of being overweight.

Methods

Data source

The NASCITA birth cohort was set up by the Laboratory for Mother and Child Health of the Istituto di Ricerche Farmacologiche Mario Negri IRCCS in Milan in collaboration with the national Paediatric Cultural Association (Associazione Culturale Pediatri, ACP).

The methods of the NASCITA cohort have been described elsewhere.11 12 Briefly, all Italian children receive primary healthcare exclusively from a family paediatrician until they are at least 6 years old as part of universalistic health system organisation. Seven well-child visits are scheduled by the paediatrician in the first 6 years of a child’s life to monitor growth and development and offer preventive care (figure 1).11 Additional visits are guaranteed when needed. The newborn population consists of all infants born during the enrolment period (1 April 2019–31 July 2020) and seen by the paediatricians for the well-child visits of the first year of life, if parental consent was given.11 12

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Figure 1

Timeline of well-child visits in the NASCITA (NAscere e creSCere in ITAlia) study.11

Some information was obtained for the NASCITA study in addition to the data routinely collected by the paediatricians during the well-child visits.11 12

During the first visit, paediatricians collected sociodemographic data regarding the parents, and information about their health status (eg, smoking habits, chronic diseases), the pregnancy and the delivery. Moreover, during the well child visits information concerning anthropometric measures of the newborns and feeding habits were collected, and during the third and fourth visits (scheduled at 6 and at 12 months of age, respectively) the paediatricians collected data on infant weaning (timing; traditional vs baby led), and on the parental perception of appetite and growth of the child.

Healthy appropriate-for-gestational age subsample

For the evaluation of factors associated with an increased BMI at 12 months, healthy newborns were selected (ie, with the exclusion of preterm and low birthweight newborns and of neonates with congenital malformations and/or admitted to intensive care unit). Moreover, the analyses were focused on neonates with appropriate-for-gestational age (AGA) birth weight, estimated using the Italian Neonatal Study charts,16 in order to monitor a cohort with homogeneous characteristics and a similar baseline risk, consistently with most of the studies that evaluated infant growth (figure 2).17

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Figure 2

Flow chart of newborns enrolled in the NASCITA (NAscere e creSCere in ITAlia) birth cohort. *Healthy newborns with appropriate-for-gestational weight attending all the first four well-child visits. AGA, appropriate-for-gestational age.

The comparison of characteristics of included versus excluded families are reported in online supplemental table S1. Slight differences were observed between the two samples, concerning the distribution by area of residence, maternal educational level and employment status, and the type of delivery.The most relevant difference was observed for the latter variable, but the lower rate of caesarean section in the AGA subsample (27.7% vs 36.7% in the sample not included) is associated to the greater prevalence of caesarean delivery in preterm and/or low birthweight neonates.

Results

The prevalence of overweight was 23.5% (95% CI 22.2% to 24.8%) in all cohort members with 12-month data (N=4270), and 23.1% (21.5%–24.6%) in the AGA subsample (N=2835).

The geographical area of residence, the age of the mother at delivery, her nationality, educational level and employment status, her prepregnancy BMI, the timing and type of weaning, the mean number of daily hours spent outdoors, the parental perception of infant appetite and growth, and the consumption of baby food were associated with different likelihoods of being overweight at 12 months of age at the univariate analyses (online supplemental table S2). More specifically, the variables more strongly associated, with the logistic regression analysis, with an increased likelihood of being overweight (table 1) were an excessive appetite (OR 3.92, 95% CI 2.40 to 6.40), living in southern Italy (OR 1.58, 95% CI 1.29 to 1.94), and traditional weaning (OR 1.43, 95% CI 1.12 to 1.83).

The same variables were associated with an increasing in BMI z score at 12 months, along with the early introduction of complementary food, the EBF and an excessive gestational weight gain, while BF for at least 12 months, the introduction of complementary food at ≥6 months of age and having an underweight mother in prepregnancy period reduced the BMI z score (table 2).

Discussion

Nearly one out of four infants resulted overweight at 1 year of age according to the WHO growth chart. This finding is the same observed in a cohort of Danish neonates,21 despite the fact that data reported for school-aged children show a greater prevalence of overweight in the Mediterranean region compared with Northern European countries.22

The geographical area of residence emerged as the main factor associated with the risk of overweight, with a 10% difference in prevalence between the North and South of Italy. Moreover, living in the South was associated with an increase in BMI z score. These data are consistent with those of other studies, which detected a twofold greater risk of being obese in school-aged children living in the southern regions.10 23 The fact that geographical differences already emerged at 12 months of age in newborns that had similar characteristics at birth strongly support the relevance of the early months of age in influencing the growth of the child.24

Italy’s southern regions are characterised by a higher poverty rate, by inequalities in provision of social and educational services, and by a worse status in several health indexes,25 and this, too, may have an impact on the likelihood of being overweight or obese. The risk of overweight in the South, however, remained significantly higher even after adjusting for several variables. It, therefore, seems that lower education and socioeconomic conditions existing in the South do not fully explain the greatest prevalence of overweight, and that cultural factors, dietary habits or genetic factors may play a role.

The association between appetite-related traits and overweight in early childhood has already been documented.26–28

Maternal unemployment was also associated with an increased risk of infant overweight. This is not consistent with other studies, which indicate that full-time employment of the mother increases the chance in children of being overweight.29–32 It should, however, be considered that most of the studies investigating the association between child weight and maternal employment status involved preschool or school-aged children, while the first year of life is a peculiar situation, since employed mothers are usually on maternity leave for 3 or more months.

Prepregnancy overweight and an excessive gestational weight gain have previously been associated with a greater BMI in infancy and childhood.33–36 This association was not observed in our study, but it is likely that this is due to the choice to include only AGA newborns, while the impact of maternal BMI starts at birth, leading to an increased chance of delivering a large-for-gestational age neonate.37

Despite the fact that evidence is not conclusive, available data suggest that BLW may be associated with a lower BMI.38 39 It has been hypothesised that BLW may improve the infant’s appetite control and lead to higher levels of satiety-responsiveness.39 This hypothesis is supported also by our findings, with an increase in BMI z score and a 43% greater likelihood of overweight in children who underwent traditional weaning.

No clear association was detected in the available studies between the timing of the introduction of complementary foods and childhood overweight40; in our analysis this association was detected when evaluating the influence on BMI z score, with an association between early weaning and an increase in BMI.

We did not find an association between BF (EBF) and overweight. Even with conflicting results, BF is associated with a reduced risk of being overweight.5–7 Most studies, however, evaluate the risk of overweight at 2 or 3 years of age, and there are few data concerning infants aged 12 months.14 In our sample, conflicting results were observed when analysing the impact on BMI z score, with an increase associated with EBF and a decrease associated with BF.

The sample was representative of the national population for distribution by geographical area of residence and environment (rural/urban), and demographic characteristics of the families.11 12 The anthropometric measures were collected by the paediatricians during the visits and, from this point of view, may be more accurate than when recorded by parents.

Our study has some limitations. First of all, there is a debate on the reliability of BMI estimate in infancy, and more in general on the validity of BMI as a predictor of adiposity and in the body composition assessment.41 42 Values of BMI at 6 or 12 months of age exceeding the 85th percentile resulted predictive of severe obesity in children,43 therefore, despite the limitations in the BMI utility we decided to use this measure, consistently with studies previously performed by other researchers.15 44 With the continuation of the NASCITA study we will evaluate which is the growth trajectories of children being overweight at 12 months.

The family paediatricians participated on a voluntary basis and most of them were educated to the best practices for supporting early child development. It is possible that they are not fully representative of Italian paediatricians, and in particular, they may be more sensitive to infant feeding and nutrition.

There were difficulties in data collection due to the COVID-19 pandemic. In particular, well-child visits were in some cases postponed and nearly 10% of infants missed one or more visits due to the parents’ fear of contagion. The characteristics of children included in this analysis were not significantly different from those of the baseline cohort, with the exception of few variables (online supplemental table S1). Moreover, BMI was estimated on the basis of the actual age at the moment of the visit, so a delay of a few weeks had a negligible impact on the data collection.

We were not able to collect information concerning the children’s dietary intake and the quality of their diets. Our definition of baby-led weaning was broad and included different attitudes. We did not, for example, have data concerning the percentage of children receiving spoon feeding or puree feeding. Finally, in the evaluation of factors associated with a greater likelihood of overweight we choose, consistently with other studies, to include only healthy newborns with an appropriate-for-gestational-age birth weight with the aim to monitor a cohort with the same baseline risk, and our results may apply only to these neonates (the majority). In any case, when considering all newborns independently of their weight-for-gestational-age, the prevalence of overweight at 12 months was very similar to that observed in AGA (23.5% vs 23.1%).

In conclusion, nearly one out of four infants in Italy are overweight. Living in the South and having unemployed mother are the main factors associated with the greatest likelihood of being overweight. Baby-led weaning resulted associated with a decreased likelihood of being overweight while, in our cohort, there were conflicting findings concerning the role of BF practice.

The involvement of parents in educational interventions, starting from the pregnancy period, may be helpful in reducing the prevalence of childhood overweight. These interventions should take into account the geographical context (ie, South of Italy) and the maternal characteristics.45