ORIGINAL ARTICLE

http://dx.doi.org/10.5546/aap.2016.eng.114

Association between the amount of sleep and obesity in Chilean schoolchildren

 

Samuel Durán Agüero M.D.^a and Pablo Haro Rivera M.Sc.^b

a. Degree of Nutrition and Dietetics. School of Health Sciences. Universidad San Sebastián. Providencia, Chile.
b. Degree of Nutrition and Dietetics. Health School. Universidad Santo Tomás, Vina del Mar, Chile.

E-mail Address: Samuel Durán Agüero M.D.: samuel.duran@uss.cl

Funding: None.

Conflict of interests: None.

Received: 7-1-2015
Accepted: 10-19-2015

 

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ABSTRACT

Introduction. Studies mainly performed in adults have shown an association between the amount of sleep and obesity.
Objective. To determine if there is an association between nocturnal sleep deprivation during the week and the weekend, eating habits, physical activity and nutritional status among Chilean schoolchildren.
Population, Material and Methods. Crosssectional study. An anthropometric assessment was done among 6-11 year-old students; the Pittsburgh Sleep Quality Index (PSQI) was used among parents to measure their children's quality of sleep; they were asked about eating habits and physical activity.
Results. One thousand eight hundred and ten schoolchildren of both sexes, attending public schools in Santiago, were assessed. Out of these schoolchildren, 49.9% slept fewer hours per night than recommended. An association in the crude model (crude OR 1.82; CI 95%: 1.29-2.56), in model 2 adjusted for cola drinks (OR 1.83; CI 95%: 1.30-2.59) and in model 3 adjusted for dinner, cola drink and caffeine beverage consumption and nocturia (OR 1.85; CI 95%: 1.30-2.62) was observed. It was also noticed that exercising was a protective factor against overweight and obesity; however, periodic limb movement during sleep was a risk factor.
Conclusions. This study showed an association between fewer hours of sleep and an increase in the risk of overweight/obesity.

Key words: Obesity; Sleep; Schoolchildren.

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INTRODUCTION

Childhood overweight and obesity are growing at an alarming rate both in developed and developing countries.^1-3 Chile is no exception: obesity in schoolchildren attending the first year of primary school has almost tripled over the last 22 years, increasing from 8.7% in 1989 to 23.1% in 2011.⁴ Childhood obesity is associated with a significant increase in the risk of developing metabolic syndrome in childhood and having chronic health conditions in adulthood, like arterial hypertension, diabetes mellitus, dislipidemia and cardiovascular disease.⁵

The causes of this obesity epidemic cannot be fully explained by changes in traditional lifestyle factors like diet (increase in food intake, serving sizes, sugar consumption, especially sugar-sweetened beverages and sweet snacks) and a decrease in physical activity.⁶

Lately, it has been proposed that a decrease in the amount of sleep can also be one of the causes leading to obesity.⁷

Some of the likely mechanisms are: (a) an alteration of neuroendocrine regulation, appetite and satiety,⁸ (b) an alteration of glucydic metabolism⁹ and (c) a deregulation of the autonomous nervous system.¹⁰

Newborn infants' sleep is considered polycyclic since there are multiple sleep-wake periods within 24 hours. On average, an infant sleeps 15 hours including short wake times.¹¹ This number of hours decreases as they grow older. It is recommended that a schoolchild aged between 5 and 10 should sleep over 10 hours.¹² Sleeping an adequate number of hours is important for the physical and psychosocial development of infants and children. A series of crosssectional and longitudinal studies have associated short sleep duration to the development of obesity.^13,14 These studies have mostly been carried out in developed countries; there is very little information about studies in developing countries.

The objective of the present study is to determine whether there is an association between nocturnal sleep deprivation during the week and the weekend, eating habits and physical activity, and the nutritional status of Chilean schoolchildren.

POPULATION AND METHODS

Cross-sectional study. Schoolchildren of both sexes attending public schools in Santiago de Chile were assessed between March and July, 2014.

The inclusion criterion required participants to be schoolchildren between 6 and 11 years old, and exclusion criteria included those schoolchildren who had not completed the assessments (anthropometric measurement or sleep survey), schoolchildren who had sleep disorders and were under medical treatment and children not living with their parents.

The power of the sample size was calculated at 95%, with a significance level of 5%. The article by Durán et al.¹⁵ was followed, providing a minimum sample of 347 schoolchildren.

The protocol was reviewed and approved by Universidad San Sebastián. Parents were asked to sign an informed consent and schoolchildren gave their assent for the assessment.

Sleep Questionnaire

The Questionnaire used was the Pediatric Sleep Questionnaire (PSQ), which validity, reliability and sensitivity values are higher than 0.80;¹⁶ it has been validated in Spanish.¹⁷ (See Annex)

The survey was conducted among the schoolchildren's parents to determine behavior during their children's sleep.

Anthropometry

The anthropometric outcome measures studied were weight, height and tricipital skinfold thickness. Weight (kg) was measured using a SECA mechanical scale, with 100 g accuracy, previously calibrated with the subject dressed in minimum clothing.¹¹ Height (cm) was obtained by measuring the subject with a portable SECA stadiometer, with 1 mm accuracy. Body mass index (BMI) was estimated by dividing the weight by the square of the height-BMI = weight (kg)/ square of the height (m²).

Nutritional status

It was classified as per the technical standard of the nutritional status assessment of a 6-18 year-old child. A schoolchild between P10 and less than P85 was considered to have a normal weight, a schoolchild between P85 and less than P95 was considered overweight and a schoolchild at P95 or higher was considered obese.

The above-mentioned measures were calculated via a standardization by professional nutritionists (using international techniques).¹⁸

Eating habits

Additionally, parents were asked whether their children had caffeine-containing beverages (coffee, tea or cola drinks) before going to sleep (consumption > 1 cup/glass/day) and if they had dinner after 9 p.m. The consumption of any caffeine-containing beverage was considered to be harmful even when occasional (1-3 times per week), because caffeine affects sleep quantity.

Statistics

Data were entered in an Excel sheet and analyzed using SPSS 22.0. To evaluate the normality of continuous variables (age, weight, height, sleeping hours), the Kolmogorov-Smirnov test was used. Regarding normal variables, the Student's t test was used; for non-normal variables, the Mann-Whitney U test was applied. Moreover, a logistic regression analysis was done to evaluate the association between sleep quantity during the week and the weekend, and the nutritional status, adjusting for cola drinks, caffeine-containing beverages, dinner consumption, nocturia, age, physical activity, limb movement and snoring; 2 adjustment models were chosen: one only with caffeine-containing beverages (this variable was used because Chileans are among the main consumers of cola drinks in the world) and the second by adding other variables. In all cases, a p value < 0.05 was considered significant.

RESULTS

One thousand eight hundred and ten schoolchildren were evaluated; 25 were excluded because their parents did not sign the informed consent, and 2 of them were under medical treatment. Out of the 25 schoolchildren, 44.5% were female; average age: 7.7 ± 1.2 years old; weight: 30.2 ± 9.4 kg; height: 129.9 ± 45.6 cm; BMI: 18.7 ± 3.1 kg/m²; hours of sleep during the week: 9.8 ± 1.0 hours; and during the weekend: 10.8 ± 1.1 hours.

Table 1 shows the anthropometric variables and hours of sleep during the week and the weekend.

Table 1. General characteristics of the sample (n: 1810)

Out of all the participants, 49.9% of sleep fewer hours than recommended during the week; this amount decreases to 16.7% during the weekend. Additionally, 51.1% of these schoolchildren have cola drinks in the afternoon-evening; 63.2% have coffee or tea before going to sleep.

The number and percentage of schoolchildren sleeping fewer hours than recommended for their age is shown in Table 2. It can be seen that sleep restriction is higher during the week than during the weekend, and that the older the age the higher the percentage of schoolchildren sleeping fewer hours than recommended; this number doubles in children aged 6 to 10.

Table 2. Number and percentage of schoolchildren sleeping fewer hours than recommended during the week and the weekend according to age

Table 3 shows data corresponding to weekdays with OR models obtained from the univariate analysis and then adjusted for cola drinks in model 2 and for dinner, cola drinks, coffee, tea and nocturia in model 3. An association in crude models as well as in model 2 and model 3 is observed between fewer sleeping hours during the week and the risk of overweight/obesity (crude OR 1.82; CI 95%: 1.29-2.56, adjusted model 2 OR 1.83; CI 95%: 1.30-2.59 and model 3 OR 1.85; CI 95%: 1.30-2.62).

Table 3. Factors associated to short sleep over the week

In the latest model, there are other factors that are positively correlated like being female (OR 1.28; CI 95%: 1.00-1.65) and experiencing limb movement during sleep (OR 1.57; CI 95%: 1.212.03), and negatively correlated, like exercising (OR 0.72; IC 95%: 0.54-0.97).

Table 4 shows data corresponding to weekends with OR models obtained from the univariate analysis and then adjusted for cola drinks in model 2 and dinner, cola drinks, coffee and tea, and nocturia in model 3. No association is observed in crude models, model 2 and model 3, and between fewer sleeping hours during the weekend and the risk of overweight/ obesity. In these latter model 2 and model 3, there are other factors positively correlated to overweight/obesity, like snoring (OR 1.42; CI 95%: 1.17-1.74), experiencing limb movement during sleep (OR 1.31; CI 95%: 1.08-1.59), having cola drinks (OR 1.45; CI 95%: 1.19-1.76), and negatively correlated like exercising (OR 0.87; CI 95%: 0.74-0.99).

Table 4. Factors associated with short sleep over the weekend

DISCUSSION

The main result of the present article is that there is an association between fewer sleeping hours during the weekend and an increase in overweight/obesity risk.

Many countries report a high incidence of sleep disorders in youth¹⁹ and, specifically in children, who, given the characteristics of present-day living, are unlikely to be able to sleep regularly or the appropriate number of hours. Health problems associated to lack of sleep, as well as the possible mechanisms of this association have also been documented.^20,21

In general, it has been described that both children and adolescents do not get enough sleep at night. Our study found that half of the schoolchildren slept less than is recommended and, therefore, were more prone to experiencing consequences the day after (for instance, feel too tired or sleepy the day after, falling asleep at school or experiencing mood disorders).²²

Additionally, both laboratory studies and epidemiological evidence point out that sleep deprivation seems to be a significant risk factor for cardiovascular and metabolic disease in adults, like obesity, type 2 diabetes and arterial hypertension, which have a negative impact on public health.^23,24

Specifically in pediatric patients, crosssectional studies from around the world show an increase in the continuous risk of obesity among children with a short duration of sleep.²⁵

A review of 22 longitudinal studies suggested a reverse association between sleep duration and the BMI among children and adolescents. A meta analysis of 11 longitudinal studies involving 24 821 participants revealed that subjects whose sleeping was within the short duration range had twice as much risk of becoming overweight or obese compared to subjects who slept for long periods (OR 2.15; CI 95%: 1.64-2.81).²⁶

Additionally, there are studies suggesting that the chronic lack of sleep from childhood up to school age in children it is associated to a higher metabolic risk²⁷ and that sleep duration reversely predicts cardiometabolic risk among obese adolescents.²⁸

The significant role of sleep in modulating hormonal release could explain the association between fewer sleeping hours and obesity. The greater risk of obesity is possibly related to the effect of decreased sleep on hormones associated to appetite control and energy expenditure, specifically, the decrease of leptin plasma levels and the concomitant increase of grelin plasma levels in subjects with sleep restriction with the consequent increase of subjective appetite.^8,29,30 Furthermore, an association between sleep restriction and the different metabolic and endocrine alterations has been suggested, including insulin resistance without a compensatory increase in insulin secretion which results in impaired glucose tolerance and an increase in the risk of type 2 diabetes.^31,32

In short, evidence suggests that chronic sleep restriction likely contributes to the present epidemic of obesity and type 2 diabetes in the population.

Chile ranks ninth among countries with the most obese children worldwide. This is mainly associated to changes in demographics, socioeconomic eating habits and physical activity;³³ however, it is necessary to consider other factors that might be contributing to this high prevalence in obesity in Chile.

In the study, it is observed that cola drink consumption in the afternoon/evening is associated to a higher risk of overweight/obesity. It is possible that, through different mechanisms, because of their caffeine content, these drinks could alter sleep patterns,³⁴ and because of sugar-sweetened beverage consumption (regardless of whether they are cola beverages or not), there is an association between this and an increase in the risk of obesity.³⁵ Cola drink consumption before sleeping is present in 96.7% of schoolchildren; Chile is one of the countries worldwide with the higher consumption of this kind of beverages, being only surpassed by Mexico and the USA.

Among the strengths of this study, we can mention that an internationally validated survey was used and that anthropometry measurements were taken to each schoolchildren; among weaknesses we can say that it is a cross-sectional study therefore, we cannot say there is causality.

It is necessary to conduct longitudinal and intervention studies that could show the effect on an improvement of the nutritional status when there is an adequate sleep hygiene, considering the insufficient sleep quantity at night described among children and adolescents.

CONCLUSIONS

In our study an association was found between fewer sleeping hours and an increase in the risk of overweight/obesity. Being female and experiencing limb movement during sleep are associated to short duration of sleep; however, exercising seems to have a protective effect.

Annex.Pediatric Sleep Questionnaire

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