Nature exposure is not associated with parent-reported or objectively measured sleep quality in 6-year-old children : a study in Finland

This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details. Author(s): Title: Year: Version: Copyright: Rights: Rights url: Please cite the original version: CC BY 4.0 https://creativecommons.org/licenses/by/4.0/ Nature exposure is not associated with parent-reported or objectively measured sleep quality in 6-year-old children : a study in Finland © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group Published version Savolainen, Katri Savolainen, K. (2023). Nature exposure is not associated with parent-reported or objectively measured sleep quality in 6-year-old children : a study in Finland. International Journal of Environmental Studies, Early online. https://doi.org/10.1080/00207233.2023.2222611 2023 Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=genv20 International Journal of Environmental Studies ISSN: (Print) (Online) Journal homepage: https://www.tandfonline.com/loi/genv20 Nature exposure is not associated with parentreported or objectively measured sleep quality in 6-year-old children – a study in Finland Katri Savolainen To cite this article: Katri Savolainen (2023): Nature exposure is not associated with parentreported or objectively measured sleep quality in 6-year-old children – a study in Finland, International Journal of Environmental Studies, DOI: 10.1080/00207233.2023.2222611 To link to this article: https://doi.org/10.1080/00207233.2023.2222611 © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. Published online: 14 Jun 2023. Submit your article to this journal View related articles View Crossmark data Nature exposure is not associated with parent-reported or objectively measured sleep quality in 6-year-old children – a study in Finland Katri Savolainen Department of Psychology, University of Jyväskylä, Jyväskylä, Finland ABSTRACT Exposure to green environments has been associated with better sleep quality in adults. This study examined whether nature exposure is associated with parent-reported or actigraphy measured sleep quality in children. Against the hypotheses, no differences in sleep quality between the case and control groups or a moderating effect of socioeconomic status or sex were found. Green environment exposure may not serve as an environmental intervention to increase sleep quality in children. KEYWORDS Nature; environment; objective; actigraphy; sleep; children Introduction Insufficient sleep and poor sleep quality are associated with a wide range of physical and mental health problems. They have been shown to have direct or bi-directional associations with, e.g. stress levels, depression, anxiety, cognitive functioning, chronic diseases, and obesity both in adults and children [1–3]. Poor sleep not only has impacts on individual level but also has major financial costs for societies [4]. It has been estimated that in the United States alone, a financial loss of $411 billion or 2.28% of the GDP in 2015, was associated with insufficient sleep [5]. Finding effective ways to improve the quality and quantity of sleep at the population-level would, thus, have an impact on both subjective well-being and financial costs at the societal level. There has been promising evidence indicating that exposure to green environments may hold potential for prevention of insufficient sleep. Exposure to green environments has been associated with very similar health and well-being effects that have been linked to better sleep quality. Exposure to greenery has been shown to buffer the adverse health effects of urban living, provide better mental and physical health, and to be associated with higher cognitive capacity and memory, and lower stress levels, both in adults and children [6–12]. And thus, it is not surprising that exposure to a green environment has also been associated with better sleep quality in most of the studies conducted [13]. The recent and the first systematic review on green space exposure and sleep quality found 13 studies on the subject matter [13]; out of which 11 studies concluded that green space exposure was associated with improvement in sleep quality [13]. These findings led to a CONTACT Katri Savolainen [email protected] Mattilanniemi 6, Jyväskylä 40100, Finland INTERNATIONAL JOURNAL OF ENVIRONMENTAL STUDIES https://doi.org/10.1080/00207233.2023.2222611 © 2023 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/ licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The terms on which this article has been published allow the posting of the Accepted Manuscript in a repository by the author(s) or with their consent. Published online 14 Jun 2023 suggestion that building green spaces and leaving unmodified nature areas in urban environments, may serve as a potential environmental intervention to increase the sleep quality at the population level. Nevertheless, remarkably little is known about how the green environment affects children’s sleep quality and quantity. As children’s overall stage in development, sleep architecture, and need for sleep are different from teenagers and adults [14,15], the results from studies in adults or youth cannot be generalised into younger children. In the systematic review by Shin et al. on green environment and sleep, 12 out of 13 studies included only adults [13] and the sole study including also children had grouped both younger and older children, aged between 6 and 17 years, in the same analyses [16]. In addition to the literature search made by Shin et al., only three recent studies researching green environment and sleep concerning children were found. Two of the studies included only older pre-teens or teenagers, aged between 10 and 15 years [17] and 12 and 17 years [18] and only one study by Reuben et al. has explored the effects on younger children of a green environment [19]. Reuben et al. showed that having parks around the home address was associated significantly more often with parent-reported inadequate amount of sleep for children aged between 0 and 5 and 6 and 12 years but not for children of 13–17 years old [19]. As the study by Reuben et al. is based on just one parent-reported question on sleep quantity [19], the current literature on green exposure, and children’s sleep quality is very limited. There is an urgent need for better understanding on the effects that green exposure has on younger children’s sleep. In addition to mixing younger children and teens in the same analyses, previous studies on green exposure and sleep quality in youth have two other methodological difficulties that complicate drawing strong conclusions from the results. First, using the green space around home as a marker of a nature exposure is problematic, as children like adults have become more sedentary. Children are spending more and more time indoors, with organised hobbies and institutions. The existence of the green places does not reliably reflect the actual time spent in greenery [20]. It is therefore suggested that actual visits to places outdoors where greenery is abundant, rather than greenery around the home, should be used when studying the effect of a green environment on well-being [21]. All the previous studies on the green environment and youth’s sleep quality have used the existence of parks and green areas near the home as indicator of green space exposure [16,18,19,22]. Second, in three out of four studies on green space and sleep in youth, the evaluation of sleep quality was based on just one [16,19] or two [17] parentreported questions on sleep quality. Although parents have been shown to report relatively accurately sleep-schedule measures, e.g. sleep onset and sleep duration, they are less accurate in assessing sleep quality measures and are overestimating the time that children spent in actual sleep and underestimating the number of awakenings during the night [23]. Therefore, it is often suggested that subjective and objective measures should play a complementary role in sleep evaluation in childhood. Study aims and hypotheses In general, the current literature lacks studies on the effect of objectively measured exposure to green environment and sleep quality in younger children. Thus, the first aim of the present study was to fill the gap in the literature and study 2K. SAVOLAINEN whether continuous and objectively measured nature exposure is associated with both subjectively and objectively measured sleep quality in 6-year-old children. The study hypothesis was that nature exposure may associate with better sleep quality. As the recent study by Jimenez et al. reported preliminary findings showing that socioeconomic status (SES) can modify the association between greenery and sleep quality in teenagers [18], the second aim of the present study was to analyse whether the moderating effect of SES can be replicated in the younger sample. Based on the previous findings [18], the hypothesis was that green space exposure may have more beneficial effects on children’s sleep in the higher SES group. The moderating effect of sex (girl/boy) was also explored. Methods Study design and participants In Finland, the municipalities have the responsibility of organising free preschool education of 4 h per working day (20 h/week) for all children living in the area. The curriculum of education is fixed, but municipalities have the right and freedom to organise education in different ways. Most commonly, the preschools organise their activities inside the day care centre or school, and the daily outdoor activities are carried out in a built playground area around the centre. These typical types of preschools make field trips to unspoilt natural sites only every now and then. There are also some preschool groups, called the nature-preschools, which devote a significant amount of time or all of it (up to a full 20 h/week) to preschool activities regularly in unspoilt natural sites, typically in nearby forest. Typically, children attend a preschool near their home, which can be either a nature-preschool or a typical preschool. Nature-preschools offer a desirable method to study the effects of nature exposure in preschool-age children. The study includes 14 nature-preschool groups around Finland and 13 typical preschool groups in the same municipality areas. All the 27 preschool groups invited to the study were willing to attend. A total of 380 families were invited to the study, and of them, 150 (39.5%) participated. Data collection was performed after the children had been in the preschool on average 4.5 (range = 2.3–8.4, SD = 1.8) months. These 150 participants form the study population for the subjective sleep quality analyses. The study population is described previously in more detail [24]. From the 150 preschool-age children, N = 50 randomly selected children (N = 30 attending nature-preschools and N = 20 attending typical preschools) attended 48 h actigraphy measurement and form the study population for the objective sleep quality analyses. The actigraphy measurements were performed during a typical preschool week. It was ascertained from the parents that during the recording days the children in nature-preschool were taking part in typical teaching days in nature and children in typical preschools were attending preschool activities indoors and at the day care centres’ playgrounds. If the children were sick at the time of the planned recording days, the days were changed. The measurement was started without delay after awakening on the first recording day and ended after awakening after the second recording night. INTERNATIONAL JOURNAL OF ENVIRONMENTAL STUDIES 3 Ethics statement The study is run under the ethical rules of the Ethics Committee of the University of Jyväskylä (Finland), which follows the Finnish nationwide ethical guidelines of the Finnish Advisory Board on Research Integrity (TENK). According to TENK guidelines, the study protocol did not present any risk of harm that would have caused further ethics committee evaluation (see Appendix 1). Written research permission was obtained from all the attending municipalities. All guardians of the study participants gave their written informed consent before the children attended the study. Objective nature exposure All the children attending the study were attending municipality-organised preschool. The objective time spent in nature during the typical preschool day was obtained from preschool managers. Nature-preschool groups spent on average 13.1 (SD = 3.55) h/week in nature and typical preschool groups on average 1.7 (SD = 0.88) h/week in nature. The children attending nature-preschool are referred to hereafter as children with objective nature exposure and children attending typical preschool as children without objective nature exposure. Parent-reported sleep quality A short version of Children’s Sleep Habit Questionnaire (CSHQ) was used to evaluate the parent-reported sleep quality. CSHQ is a retrospective parent-reported questionnaire that has been developed for children aged 4–10 years of age for screening childhood sleep disorders over a typical week [25]. A version of CSHQ, with 31 items, was used in the present study. And thus, compared to the original questionnaire [25] the daytime sleepiness subscale is calculated with six items, instead of eight. There are several previous studies that have shown that shorter versions of CSHQ can be used to evaluate sleep quality in children [26–28]. Versions of 24 items [28], 23 items [26] and 19 items [27] have been used. Questions in the CSHQ are rated on a 3-point Likert-type scale (rarely/0–1 times per week = 1, sometimes/2–4 times per week = 2, usually/5–7 times per week = 3), assessing the frequency of sleep disturbances [25]. CSHQ provides a total sum score (range = 31– 93 in this study). A higher value indicates more sleep problems. CSHQ includes the following subscales: bedtime resistance (range = 8–24), sleep onset delay (range = 1–3), sleep duration (range = 3–9), sleep anxiety (range = 4–12), night wakings (range = 3–9), parasomnias (range = 7–21), sleep-disordered breathing (range = 3–9), and daytime sleepiness (range = 6–18 in this study) [25]. The internal reliability (Cronbach’s α) of 31-item short version of CSHQ in this study was 0.70. Objective sleep quality Objective sleep quality was measured using accelerometer ActiGraph GT3X+ (ActiGraph, Pensacola, USA). Children wore actigraphy on the non-dominant wrist for 48 h, including two overnight periods during a typical preschool week. ActiGraph 4K. SAVOLAINEN GT3X+ worn at the wrist has been shown to be a good movement-based measurement tool for sleep quality metrics in 5to 8-year-old children [29]. The devices were initialised using 10 s epochs and processed with the normal frequency filter. For sleep parameter calculations, 60 s epoch data was reintegrated from the original 10 s epochs. Sadeh algorithm [30] was used for assessing sleep quality parameters. Sadeh algorithm is a commonly used algorithm in children and is has been well validated also in children against polysomnography [30–32]. The following parameters were gathered from the data: sleep latency, total sleep time, wake after sleep onset, efficiency, number of awakenings (>1 min), duration of >15 min awakenings, and fragmentation index. A minimum of 22 h measurement across 24 h measurement period was the chosen wear time criteria used for the subsequent analysis. All the data fulfilled the criteria. Actigraphs were initialised, data saved, and sleep parameters calculated using Actilife (V 6.13.3) software. Socioeconomic status (SES) SES was operationalised from a question on the parent’s self-reported highest attained education. Parent was asked to report their own and their spouses highest attained education using four categories. If both the parent’s highest attained education was either basic education or vocational school, the variables were recoded into value 0 (N = 45, 30.2%) representing the lower SES category. If either of the parent’s highest attained education was bachelor’s degree or higher university degree, the variables were recoded into value 1 (N = 104, 69.8%) representing higher SES category. Frequency of visiting nature in free time Frequency that the child typically visits nature during free time was collected from the parent. The parents were asked: ‘“When your child is outdoors, how often he/she spends time in the forest or other unspoilt natural sites (after the day care or during a day off)?”’ using six categories (rarely, less frequently than weekly, once a week, twice a week, three to four times a week, and five to seven times a week). In all the analyses, the variable was recoded into a dummy variable where value 0 (N = 55, 36.9%) represents spending time in nature less frequently than weekly and value 1 (N = 94, 63.1%) spending time in nature at least once a week. Statistical analyses Linear regression analysis was used to examine the associations between objective nature exposure and continuous sleep quality variables and logistic regression to analyse the categorical sleep variables. Subjective and objective sleep quality variables were used as dependent variables. All the main effect analyses were run using both dummy coded and continuous nature exposure variables. Dummy coded `nature exposure status´ variable divided children into two categories; children who attended nature-preschool and thus experienced objective nature exposure (value 1) vs. children who were attending typical preschool INTERNATIONAL JOURNAL OF ENVIRONMENTAL STUDIES 5 and thus did not experience objective nature exposure (value 0). Average time (hours) spent in nature during preschool week was used as continuous nature exposure variable. Sum scores for CSHQ and its subscales were calculated. Six questions in CSHQ are asked in reverse form [25] and thus were reversed before calculating the continuous sum scores. Seven out of eight CSHQ subscale sum scores (bedtime resistance, sleep onset delay, sleep duration, sleep anxiety, night wakings, parasomnias, sleep-disordered breathing) were skewed to the right and thus, were natural log (ln) transformed prior to the statistical analyses. For more detailed analyses, the CSHQ sum score and all its eight subscales were dummy coded into categorical variables. Dummy coded CSHQ variables were calculated by dividing the continuous variables into two groups split from the median, where value 0 represents fewer sleep problems and value 1 more sleep problems. The median split for CSHQ sum score was used, instead of the original cut-off score 41 reported by Owens [25] because of its low threshold level documented in the previous studies. It has been shown that the original cut-off score can generate up to 96% of children to be categorised with possible sleep disturbances [33]. Objective sleep quality variables extracted from actigraphy for the two measurement nights were averaged into a mean for the analyses. Aggregated natural sleep pattern variables have been shown to be reliable when using shorter overall measurement period [34]. One Actigraph-measured objective sleep quality variable, duration of >15 min awakenings, was skewed to the right and was natural log (ln) transformed prior to the statistical analyses. The sleep latency of one child was 117 min, where for the rest of the children, the latency was less than 47 min. The sleep latency analyses were thus run both with and without the outlier value. None of the non-significant results became significant when the participant was excluded from the analyses. Interaction effects of `SES x nature exposure status´ and `sex x nature exposure status´ were run with CSHQ sum score and objectively measured sleep variables. The interaction terms were calculated and added into the linear regression model together with the main effects. Both unadjusted and covariate adjusted analyses were run. All the analyses first run without covariate adjustment are referred to as Model 1 analyses. All the significant results from Model 1 analyses were re-run with the following Model 2 covariates: sex, age, SES, frequency of visiting nature in free time. All the statistical analyses were carried out using SPSS 26 for Windows. Results The participants (N = 150) were on average 6.5 (SD = 0.3) years old at the time of the measurement and 73 (48.7%) of them were girls. Objectively measured sleep latency for all the children was on average 17.9 (SD = 17.9) min and objectively measured average quantity sleep for all the children time 8 h and 27 min (SD = 27.9 min). There was no difference in SES, age, sex, or time spent in nature during free time between the children with and without objective nature exposure (Model 1 p-values >0.093 See Table 1). Children with objective nature exposure spent significantly more time in nature during preschool than children without objective nature exposure (Model 1 p < 0.001, see Table 1, Model 2 p < 0.001). Children with objective nature exposure spent on average 6K. SAVOLAINEN 13.1 (SD = 3.55) h/week in nature and children without objective nature exposure on average 1.7 (SD = 0.88) h/week in nature. None of the background characteristics, including age, sex, SES, and frequency of visiting nature in free time, were associated with SCHQ sum score (Model 1 p-values >0.149). From the background characteristics, the age of the children was associated with objectively measured duration of >15 min awakenings during the night (Model 1 p = 0.018, 95% CI = −1.428, −0.145; Model 2 p = 0.009, 95% CI = −1.607, −0.251), so that older children had less 15 min or longer awake periods during the night than younger children. None of the other background characteristics were associated with objectively measured sleep variables: sleep latency, total sleep time, wake after sleep onset, sleep efficiency, number of awakenings (>1 min), fragmentation index, or duration of >15 min awakenings (Model 1 p-values >0.055). Nature exposure and subjective sleep quality (N = 150) There were no differences in parent-reported CSHQ sum score or any of its subscales between the children with and without objective nature exposure when CSHQ was used as continuous (Model 1 p-values >0.149) or binary (Model 1 p-values >0.168) variables (see Table 2). Average time spent in nature during preschool week was not associated Table 1. Background characteristics of study population (N = 150) divided between children with objective nature exposure and children without objective nature exposure. Children with objective nature exposure (N = 85) N (%), Mean (SD) Children without objective nature exposure (N = 65) N (%), Mean (SD) p Time spent in nature during preschool (h/week) 13.1 (SD = 3.5) 1.7 (SD = .9) <.001* Frequency of visiting nature in free time (weekly) 55 (65%) 39 (61%) .640 Age (years) 6.5 (SD = .3) 6.5 (SD = .3) .730 Sex (girl) 39 (46%) 34 (52%) .439 Socioeconomic status (higher) 64 (75%) 40 (62%) .093 N = Number of cases, SD=standard deviation, * = p < 0.05 in Model 1 analyses. Table 2. Unadjusted (Model 1) differences in parent-reported CSHQ sleep variables (N = 150) between children with and without objective nature exposure during preschool using continuous and binary sleep variables. CSHQ continuous binary 1 95% CI p Exp(B) p Sum score −0.044, 0.062 .734 .961 .904 Subscales Bedtime resistance −0.090, 0.051 .586 .910 .788 Sleep onset delay −0.138, 0.049 .346 .589 .254 Sleep duration −0.020, 0.124 .158 1.500 .244 Sleep anxiety −0.091, 0.060 .685 .873 .690 Night wakings −0.122, 0.050 .405 .630 .168 Parasomnias −0.047, 0.070 .699 1.087 .800 Sleep-disordered breathing −0.028. 0.104 .258 1.634 .322 Daytime sleepiness −0.117, 0.136 .883 1.176 .631 CSHQ= Child Sleep Habit Questionnaire. 1=two groups split from median value, 95% CI = 95% confidence interval, Exp(B)= Exponentiation of the B coefficient. INTERNATIONAL JOURNAL OF ENVIRONMENTAL STUDIES 7 [17] Feng, X., Flexeder, C., Markevych, I., Standl, M., Heinrich, J., Schikowski, T., Koletzko, S., Herberth, G., Bauer, C.-P., von Berg, A., Berdel, D., Astell-Burt, T., et al., 2020, Impact of residential green space on sleep quality and sufficiency in children and adolescents residing in Australia and Germany. 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