CLINICAL REVIEWBidirectional associations between sleep and dietary intake in 0–5 year old children: A systematic review with evidence mapping
Introduction
While individual countries have reported a stabilisation of obesity rates in young children, the global prevalence of obesity in children under the age of five continues to rise [1]. Weight status tracks from childhood onwards [2], with overweight children likely to remain overweight as adults [1], facing an increased risk of non-communicable diseases over the life course [3]. It is well-established that prevention is key to improving childhood obesity rates, and that infancy to early childhood is a critical period for developing healthy eating and activity habits that persist into later life [1,3,4]. While diet and physical activity have long been cornerstones of obesity prevention strategies, difficulties in modifying these behaviours in the long-term suggest that investment in other approaches is warranted [5].
Such an approach might be via sleep, given that short sleep duration has been identified as a strong, independent risk factor for obesity in children, including infants [[5], [6], [7], [8], [9]]. Indeed, two recent trials have determined that sleep interventions during infancy can benefit weight long-term [10,11]. However, the mechanism(s) whereby insufficient sleep leads to increased weight gain are uncertain [5,[12], [13], [14]], although thought to be mediated primarily through an increase in dietary energy intake [12]. A recent systematic review and meta-analysis in children aged two to 18 y indicated that short sleep was associated with unhealthy dietary habits and positive energy balance [15]. These studies have shown that shorter sleep leads to a greater energy intake [16] or a preference for more calorie-dense and sweeter foods [16,17] in teenagers, with similar outcomes observed among preschool [18] and school aged children [19].
However, there are challenges with assessing relationships between sleep and diet, particularly in infants and toddlers as their dietary needs and sleep requirements change rapidly [20,21], and subjective methods of data collection introduce bias. While studies have investigated associations between sleep and macronutrient intake (fat, protein, and carbohydrate), sleep and micronutrient intake (vitamins and minerals), and sleep and small metabolites (such as amino acids and phenolic compounds) [22], the possible bi-directional nature of the relationship between sleep and diet (where it is equally feasible that sleep affects diet as diet affects sleep) has not been explored [23]. Perhaps this is why, despite the considerable health impacts of obesity on population risk factors for non-communicable disease and premature mortality, few systematic reviews of sleep and diet have been conducted for children aged five years or younger.
This review investigates the bidirectional associations between sleep and diet in children aged five years and younger. We define the eligible studies in this area with evidence mapping [24], identifying knowledge gaps with a visual presentation of research topics and study types as well as the methods used to measure sleep and dietary intake in the existing literature. We conclude by suggesting future directions in the study of sleep and diet in children.
Section snippets
Methods
We followed PRISMA processes and reporting standards for systematic reviews and meta-analyses [25,26]. This review was prospectively registered in the PROSPERO International Prospective Register of Systematic Reviews (CRD42018091647). Literature searches, identification of eligible trials or studies, data extraction, and bias assessment were undertaken independently by at least two researchers (SK and LJF), with discrepancies resolved with an additional reviewer (ALW or ANR). Data extracted
Results
Of 10,898 records initially identified, 17 eligible trials of 2678 participants, 16 eligible cohort studies of 65,265 participants, and 17 eligible cross-sectional studies of 4548 participants were identified (see Fig. 1). Identified trials and studies were from North America (38%), Europe (38%), Asia (10%), the Middle East (6%), South/Central America (4%), Australia (2%), and Africa (2%). An evidence map summarising the included studies by topic and study type is shown in Fig. 2. Most studies
Risk of bias
Risk of bias summaries are shown in Fig. 6. Most trials were of unclear risk of bias for their sequence generation and allocation concealment and blinding of participants and staff. High risk of bias was identified for sequence generation (4 of 17), blinding of participants (3 of 17), and then one study each for blinding of outcomes, incomplete outcome data, or other (no washout period in a cross over design with likely carryover effects). Only one (7%) of the 17 trials considered the adequacy
Discussion
This systematic review of sleep and diet among children aged five years and younger illustrates that poor sleep is consistently associated with poor dietary outcomes, although the number of studies included was small. A greater number of studies had examined the effect of diet on sleep, with variable findings. Much of the literature was cross-sectional in nature, with no ability to determine direction of the relationship. Meta-analysis of data was not possible due to heterogeneity between
Conclusion
It is increasingly apparent that obesity in young children often persists into adolescence and adulthood [3,34], as habits laid down in childhood tend to continue into later life [2], indicating that children may be an ideal population to target with sleep interventions for obesity prevention [18,19,34]. Instead of simply including sleep alongside a host of other lifestyle factors, researchers should design studies that isolate sleep measures in order to assess the associations between sleep
Author contributions
ALW and ANR contributed equally to this work. RWT, ANR, and ALW led the research. ANR developed the search strategy. SK and LF conducted article screening and quality assessments. ALW and ANR conducted screening checks and resolved conflicts. ANR conducted quality assessment checks and created associated figures. ALW created figures and tables. ALW, ANR, SK, and RWT drafted the manuscript, and ALW finalised it. All authors contributed to the review of drafts and read and approved the final
Funding
Funding sources are the postdoctoral fellowships of the 2 co-first authors (Ward and Reynolds) obtained from the University of Otago Dept of Medicine.
Conflicts of interest
The authors do not have any conflicts of interest to disclose.
Acknowledgments
The authors wish to thank Dr Josie Athens and Dr Pouya Saeedi for their generous time in translating some full text articles for review. The authors are also grateful for the guidance of their research librarian, Richard German.
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Aimee L. Ward and Andrew N. Reynolds are co-first authors of this work.
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The most important references are denoted by an asterisk.