Original ArticleChanges in sleep duration in Spanish children aged 2–14 years from 1987 to 2011
Introduction
The importance of sleep in childhood in terms of quality and duration is increasingly coming under scrutiny. Not least because of the short term and long term consequences. Childhood sleep patterns are thought to potentially continue on into adulthood [1]. Sleep in early childhood is important for cognitive, psychological development and growth [2]. Furthermore, short sleep duration in childhood has been associated with obesity, poor academic performance, behavioral problems and affects physical and mental health as well as secondary effects impacting on the family [3], [4], [5].
Sleep duration during childhood and adolescence is determined by a mix of genes and environment, with a higher influence from the shared environment [1], [5]. Sleep duration has a large cultural component [5] and factors found to be associated in previous studies include family environment, demographic factors, health status and parental sleep habits [1], [2]. Understanding cultural and regional variations in sleep duration is important when considering sleep duration norms, and recommendations and defining sleep problems.
International studies report a decreasing trend in sleep duration [6], [7] and little is still known of the long term impact this will have during childhood and adulthood in terms of both physical and mental health. Given the increasing trend in child obesity, sleep duration may be an important modifiable contributing factor and some previous studies have shown an association between the two [2], [8], [9], [10], although this is inconsistent [11]. Despite young children having less control over their food intake, it is still hypothesized that short sleep increases overweight risk via higher energy intake [12]. Other mechanisms including hormonal regulation and decreased energy expenditure due to fatigue have also been proposed [9].
As far as we are aware, no other studies have been published on the trends of sleep duration during childhood and adolescence in Spain. We investigate the sleep duration trends for children in Spain from 1987 to 2011 and associated socio-demographic characteristics.
Section snippets
Study design and population
This study used data collected by the Spanish Ministry of Health and National Institute of Statistics in a series of cross-sectional National Health Surveys in 1987, 1993, 1995, 1997, 2001, 2003/2004, 2006/2007, and 2011 [13]. Data were collected in a multi-stage stratified random sample, with strata based on municipality size. Questionnaires were conducted in person by a trained interviewer. In 2011, computer-assisted personal interviews were used. Our population sample was restricted to
Results
The mean sleep duration by age from 1987 to 2011 is shown in Table 1. The downward trend was found to be statistically significant in each age group: decreasing from 10 hours 40 minutes in 2- to 5-year-olds in 1987 to 10 hours 16 minutes in 2011 (Standard error 4.38 minutes); decreasing by 20 minutes from 9 hours 51 minutes in 1987 for 6- to 9-year-olds to 9 hours 31 minutes in 2011 (Standard error 2.82 minutes), and in 10–14 year olds decreasing from 9 hours 19 minutes in 1987 to 8 hours 52
Discussion
Our study results clearly show a statistically significant decrease in 24-hour sleep duration in children aged 2–14 years over the last two decades. This is consistent with other international studies [7], [19], [20]. With a decrease in average sleep duration of about 20 minutes or more in each age group from 1987 to 2011, this downward trend is slightly higher than the −0.73 minutes per year reported by Matricciani et al. [7] This downward trend is reflected in the increasing percentage of
Conclusion
The downward sleep duration trend in all demographic groups is worrisome, and long-term health outcomes are still unclear. With the association of short sleep duration with many different health outcomes, we should be investigating and considering sleep as a modifiable lifestyle factor and a public health issue. Lack of consistency in cut-offs for age-appropriate ideal sleep in literature is a barrier for international comparison and highlights the need for research in physiological sleep
Conflict of interest
The authors declare no conflicts of interest.
The ICMJE Uniform Disclosure Form for Potential Conflicts of Interest associated with this article can be viewed by clicking on the following link: http://dx.doi.org/10.1016/j.sleep.2015.12.021.
Acknowledgements
These results and this work were undertaken as part of the PhD research of Ingrid de Ruiter. All authors were involved in writing the paper and had final approval of the submitted and published versions.
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