Background
The relationships between physical growth and neurodevelopment are found; however, the literature for infants, especially within term-born, is relatively few [
1,
2]. As far as we know, the outstanding cohort study, which named Avon Longitudinal Study of Parents and Children (ALSPAC), has paid attention to this relationship. They found that physical growth in adults and children were not associated with neurodevelopment, suggesting that physical development in early life may be a critical period of later neural development [
3]. Between birth and 1 year, body weight has triples, body length increases by more than 50%, and brain volumes increase to 75% of an adult’s size [
4].
Besides, although recent studies have found that bidirectional effects between physical growth and neurodevelopment, that is, physical growth may be both influencing and responding to infants, few studies have the analysis of these relationships. On the one hand, physical growth may be a sign of disruption of the critical steps during brain development. The brain and nervous system growing at its fastest rate during this time, such as weight status and weight gain during this process, can have long-term impacts on the brain’s developing structure and function [
5‐
8]. Moreover, research addressing children’s physical growth on neurodevelopment has shown controversial findings. Some studies found that weight status has been negatively associated with neurodevelopment, especially in motor development and cognitive development. However, longitudinal studies confirmed no temporal associations in the population [
9‐
12]. On the other hand, the state of neurodevelopment in young children might also affect physical development [
13,
14]. However, few epidemiologic studies that focus on the effects and have shown controversial findings [
15]. Although a comprehensive systematic review study showed infants with better development in psychiatric and neurological demonstrated a greater gain in height and weight gain between 4 and 12 months, the study to explore early development (SEED) showed infants with intellectual disability and neurodevelopmental impairments, in particular, would be at greater risk for rapid weight gain or obesity during infancy [
16].
The bidirectional relationships between early life neurodevelopment with physical growth can be affected by numerous confounding factors. As these factors are often complex and interdependent, using independent regression models is cumbersome. In this paper, the study needs to explore the relationships between physical growth and neurodevelopment during infancy, and investigate causal pathways beginning in early life. The cross-lagged analysis should be used to overcome these problems, which is a powerful statistical approach to address methodological problems.
In this study, we considered to use the cross-lagged models and utilize data from the Born in Shenyang Cohort Study (BISCS) to characterize the bidirectional associations of term-born infants’ neurodevelopment in five domains (adaptive behavior, gross motor, fine motor, language, and social behavior) and physical growth (Body Mass Index (BMI) Z -score and weight gain velocity) in the early life.
Discussion
To the best of our knowledge, the current study is one of the few to explore the bidirectional associations between neurodevelopment, as assessed by the Gesell Development Scale, and physical growth among term-born infants. Our birth cohort study suggests the negative associations between gross motor and social behavior at the age of 6 months with weight status at the age of 12 months. Regarding the opposite direction of relationship, a higher infant Z -scored BMI at the age of 6 months predicted a lower neurological development level in the gross motor at the age of 12 months. Gross motor performed a bidirectional relationship, although neurological development level had a more significant effect on infants’ BMI Z -score than the opposite. Similar associations had been found in weight gain velocity.
In motor abilities, our findings are consistent with previous studies demonstrating that gross motor skills were negatively associated with infant physical growth in both directions [
29]. Our results indicate a bidirectional causal temporal relationship between gross motor skills and infant physical growth, which means that an increase in physical index or in gross motor capacity can cause each other to decline. In clinical practice, more attention should be paid to physical development or neural development, which is beneficial to strengthen the predictive function of each other. However, Schmidt et al. found minimal correlations between motor development and weight status, suggesting that weight status and motor milestones are mostly independent of one another [
30]. There are several possible reasons for these differences. First, the samples were analyzed in different age groups. Most recent studies concentrate on exploring relationships in preschool children or school-aged children, whereas the participants in our study were infants, especially within term-born infants. Second, differences may have arisen due to the fact that different tools measured the participants. The current study evaluated motor skills using the GDS, which were in line with motor milestones and dependent on the age interval of the infants. However, this scale is still heterogeneous with other measurement tools. Potential mechanisms for these effects include the possibility that infants with poor gross motor performance are frequently associated with biomechanical problems and morphological constraints on tasks involving changes in overweight/obese status and fat mass [
31]. However, Gentier and colleagues suggested that a deficit in childhood motor skills should be examined in a broader sense, rather than a mechanical interpretation. For example, it is plausible that the reduced physical activity and the lack of decision-making, planning, and control functions in infants with poor motor ability are causal factors in obese status, suggesting that impaired motor development is also related to children with obesity [
12]. Therefore, additional exploratory analyses to determine the bidirectional associations between motor domains and weight status should be conducted.
Consistent with our results, previous studies observed the relationships between social skills and infant’s physical development [
32]. According to the Infant Research framework [
33], infant social communication abilities develop in dynamic functional interactions between mothers and infants. Ostensibly, it should be recognized that the relationship between mother and infant is bidirectional and may influence infant clues’ accuracy. As infants grow, they use communicate abilities to express wants or dislike certain foods [
34]. Suppose infants have poor social skills, such as infrequent laughter, reduced focus, shared attention, and/or unclear signals to articulate their needs (including the cues of full or hungry). In that case, it may preclude their potential development of caregivers’ feeding responsiveness [
35]. Scholars propose that maternal responsiveness to their children’s expressions, such as appetite, hunger, and satiety is essential when developing a healthy diet and could play an essential role in offspring weight status [
32]. Besides, it is generally known that language and social competence can be simultaneously discussed as previous studies have demonstrated that children’s social and language development are synchronized mainly [
36]; however, no relationship between language ability and body weight was found in our study. Additional research is needed to investigate further the potential contribution of children’s social communication skills and language ability to maternal factors.
Our prospective study provided a unique opportunity to explore the bidirectional relationships between infants’ neurodevelopment and physical growth and had attempted to analyze the associations of mutual prediction, which have been of little attention to date. In our study, the bidirectional relationships between term-born infants’ neurodevelopment of gross motor with physical growth are found. However, there are also several limitations. First, our study is limited in sample size and follow-up time, then might weakly predict later attainment. Nevertheless, physical and neurological development in early life is irreversible 3. Based on this study, long-term follow-up data will be used to verify our research results further. Second, Confounding factors, such as feeding style (responding style, authoritative feeding, etc.), breastfeeding (bottle or exclusive breastfeeding) were not fully adjusted.
Acknowledgements
We thank all the participants who took part in our study, and interviewers, nurses, computer and laboratory technicians, clerical workers, research scientists, volunteers, managers, and receptionists of the BISCS study for their supports and dedications. The study was supported by China Postdoctoral Science Foundation (2019 M661179).
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