Sleep and BMI in South African urban and rural, high and low-income preschool children

Dale E Rae,Catherine E Draper,Shane A Norris,Rachel A Jones,Kathleen Kahn,Trina Hinkley,Simone A Tomaz,Rhian Twine

doi:10.1186/s12889-021-10591-5

Abstract

BackgroundThe extent to which income setting or rural and urban environments modify the association between sleep and obesity in young children is unclear. The aims of this cross-sectional observational study were to (i) describe and compare sleep in South African preschool children from rural low-income (RL), urban low-income (UL) and urban high-income (UH) settings; and (ii) test for associations between sleep parameters and body mass index (BMI).MethodsParticipants were preschoolers (5.2 ± 0.7y, 49.5% boys) from RL (n = 111), UL (n = 65) and UH (n = 22) settings. Height and weight were measured. Sleep, sedentary behaviour and physical activity were assessed using accelerometery.ResultsUL children had higher BMI z-scores (median: 0.39; interquartile range: − 0.27, 0.99) than the UH (− 0.38; − 0.88, 0.11) and RL (− 0.08; − 0.83, 0.53) children (p = 0.001). The UL children had later bedtimes (p < 0.001) and wake-up times (p < 0.001) and shorter 24 h (p < 0.001) and nocturnal (p < 0.001) sleep durations than the RL and UH children. After adjusting for age, sex, setting, SB and PA, for every hour less sleep obtained (24 h and nocturnal), children were 2.28 (95% CI: 1.28–4.35) and 2.22 (95% CI: 1.27–3.85) more likely, respectively, to belong to a higher BMI z-score quartile.ConclusionsShorter sleep is associated with a higher BMI z-score in South African preschoolers, despite high levels of PA, with UL children appearing to be particularly vulnerable.

Highlights

The extent to which income setting or rural and urban environments modify the association between sleep and obesity in young children is unclear
Shorter sleep is associated with a higher body mass index (BMI) z-score in South African preschoolers, despite high levels of physical activity (PA), with urban lowincome (UL) children appearing to be vulnerable
The rural low-income (RL) children engaged in less sedentary behavior than the UL (p < 0.001) and urban high-income (UH) (p = 0.006) children, while the UH children accumulate less LPA and Light- to vigorous-intensity physical activity (LMVPA) compared to the UL (LPA: p < 0.001, LMVPA: p < 0.001) and RL (LPA: p < 0.001, LMVPA: p < 0.001) children

Summary

Introduction

The extent to which income setting or rural and urban environments modify the association between sleep and obesity in young children is unclear. South Africa (SA) is an upper middle-income country characterised by large discrepancies in socioeconomic status (SES) with nearly half of the population (49.2%) living in poverty [11] in both rural and urban settings It is undergoing an epidemiological transition; obesity is on the rise across all age groups [12] and noncommunicable diseases are responsible for more deaths annually than infectious diseases [13]. This study observed short nocturnal sleep (9.3 ± 0.8 h) in preschool-aged children in an urban, low-income setting in SA, where even after the inclusion of daytime naps, 24 h sleep duration was less than 10 h in 38% of the children [19] Whether or not this observation of shorter sleep is present in the rural setting or is a consequence of income status has not been established in this age group. The aims of this study were to (i) describe and compare sleep in preschool-aged South African children from rural lowincome, urban low-income and urban high-income settings and (ii) test for associations between sleep and body mass index

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Results

Discussion

Conclusion