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The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study
ORCP-595; No. of Pages 7
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Obesity Research & Clinical Practice (2016) xxx, xxx—xxx
ORIGINAL ARTICLE
The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study Chia-Ling Lin a, Chun-Ping Lin b, Shu-Wen Chen a, Hsueh-Ching Wu c, Yu-Hsia Tsai d,e,∗ a
Department of Nursing, Chang Gung University of Science and Technology, Taoyuan, Taiwan b Department of Nursing, Shu-Zen Junior College of Medicine and Management, Kaohsiung, Taiwan c Department of Nursing, Hsin Sheng College of Medical Care and Management, Taoyuan, Taiwan d Department of Nursing, College of Medicine, Chang Gung University, Taoyuan, Taiwan e Department of Cardiovascular Medicine, Chang Gung Memorial Hospital, Taoyuan, Taiwan Received 19 December 2015 ; received in revised form 20 July 2016; accepted 25 July 2016
KEYWORDS Sleep duration; Overweight; Obesity; Body mass index; Adults
Summary Background/objective: The effect of eating habits and sedentary lifestyle on obesity has been extensively examined and supported; however, few studies have examined the association of sleep duration with obesity in Taiwan. To redress this gap, this study investigated the association of sleep duration with overweight and obesity in community-dwelling Taiwanese adults. Methods: A cross-sectional study was performed using the 2005—2008 Nutrition and Health Survey in Taiwan (NAHSIT). A logistic regression model was used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) of the association of sleep duration with overweight and obesity. Nightly sleep duration was divided into three groups: >6 to <9 h (normal), ≤6 h (short), and ≥9 h (long). Results: A total of 1548 adults aged 20—64 years were examined in this study. The adjusted ORs of obesity for short and long sleep duration relative to a normal sleep duration were 1.31 (95% CI 1.01, 1.76) and 1.64 (95% CI 1.04, 2.61), respectively. No significant association of sleep duration with overweight was observed.
∗ Corresponding author at: Department of Nursing, College of Medicine, Chang Gung University, Taoyuan, Taiwan; Department of Cardiovascular Medicine, Chang Gung Memorial Hospital, Taoyuan, Taiwan; No. 259, Wenhua 1st Rd., Guishan Dist., Taoyuan 33302, Taiwan. Tel.: +886 3 2118800 ext 5184. E-mail address: [email protected] (Y.-H. Tsai).
http://dx.doi.org/10.1016/j.orcp.2016.07.005 1871-403X/© 2016 Asia Oceania Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Lin C-L, et al. The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study. Obes Res Clin Pract (2016), http://dx.doi.org/10.1016/j.orcp.2016.07.005
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C.-L. Lin et al. Conclusions: The present study suggests that both short and long sleep duration are associated with obesity risk. © 2016 Asia Oceania Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.
Introduction
Methods
Over the few decades, obesity has become a common epidemic disease [1]. Evidence has indicated that obesity negatively affects health outcomes and increases health care costs. Moreover, obesity prevention has become a critical health concern and has been addressed in several countries [2]. A study reported that obesity results from complex multifactorial interactions, such as those involving genes, eating habits, sedentary lifestyle, and environment [3]. Studies have reported an association of short sleep duration with obesity risk [4—6]. Moreover, experimental studies have indicated that a decrease in sleep duration is associated with changes in orexins, including increased ghrelin and decreased leptin [7—9]. By contrast, other studies have reported that no significant association of sleep duration with body mass index (BMI) [10,11]. This contradiction indicates the necessity of further research to verify the relationship between these two factors. Prior study indicated that the association of sleep duration with obesity may be affected by racial disparities [12]. For instance, African Americans are more susceptible to the curtailment of sleep duration and have a higher risk of obesity than Caucasians [13]. Compared to the Western society or other Asian countries, both sleep duration and obesity have been extensively surveyed [4—6,14,15]. In Taiwan, one study reported that adolescents who frequently obtained 6—8 h per night had a decreased probability of becoming overweight [16]. In addition, the paucity of studies addresses the correlation between sleep duration and weight abnormality in Taiwanese adults. Therefore, this study investigated the association of varying sleep durations with overweight and obesity in Taiwanese adults aged 20—64 years based on the 2005—2008 Nutrition and Health Survey in Taiwan (NAHSIT).
Data sources We performed a secondary database analysis using data from the 2005—2008 NAHSIT a populationbased cross-sectional study performed using a stratified multistage cluster sampling method. The details of the sampling method have been reported in previous studies [17,18].
Inclusion criteria for participation The study population included community-dwelling adults aged 20—64 years who participated in the 2005—2008 NAHSIT. In total, 1548 participants who completed both the physical examination and questionnaire form were included in the current analysis.
Definitions of sleep duration, overweight, obesity, waist circumference, hypertension, and type 2 diabetes The participants described their sleep duration during weeknights (Sunday—Thursday) and weekends (Friday and Saturday) in the previous week. We used the following formula described by Hall et al. to determine sleep duration: ((5 × weekday standard deviation (SD)) + (2 × weekend (SD))/7) [19]. Furthermore, we divided nightly sleep duration into the following three groups according to a previous study [20]: short (≤6 h per night), normal (>6 to <9 h per night), and long (≥9 h per night). Overweight/obesity: BMI was calculated as weight (kg) divided by height (m2 ) [21]. Height and weight were measured to the nearest 0.1 cm and 0.1 kg, respectively [18]. Overweight and obesity were defined as BMI 24—26.9 and BMI ≥ 27, respectively, in accordance with criteria for Taiwanese adults defined by the Ministry of Health and
Please cite this article in press as: Lin C-L, et al. The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study. Obes Res Clin Pract (2016), http://dx.doi.org/10.1016/j.orcp.2016.07.005
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Sleep duration and overweight or obesity Welfare, Taiwan. Waist circumference (WC): WC was measured at the midpoint between the lower border of the rib cage and the top of the iliac crest [22]. Hypertension was defined on the basis of the selfreported previous history of hypertension or the present use of antihypertensive drugs. Type 2 diabetes was defined on the basis of the participants’ fasting plasma glucose level of ≥126 mg/dL or the present use of antidiabetic drugs.
Ethical approval This study was approved by the Research Ethics Committee of National Taiwan University Hospital (201503123W).
Statistical analysis All statistical analyses were performed using the SPSS software (Version 21; SPSS Inc., Chicago, IL, USA). For descriptive statistics, basic information was expressed as percentages, means, and SDs. For inferential statistics, a one-way ANOVA was performed to examine the distribution and difference of continuous variables with varying SDs. The Chi-square test was used to calculate the odds ratio (OR) and 95% confidence interval (CI) of the dependent variable for each independent variable. Furthermore, a multiple logistic regression was used to calculate the OR value of the dependent variable in the multivariate analysis after adjustment for confounders. A significance level of ˛ = 0.05 was used.
Results In total, we included 1548 adults aged 20—64 years (739 men and 809 women), with average age of 43.5 years (SD = 12.1). The proportion of women was higher than that of men and accounted for more than half of the participants. The mean BMI of the participants was 24.4 kg/m2 (SD = 4.1), and the mean sleep duration was 7.0 h (SD = 1.3) (Table 1). Table 2 shows that after adjustment for confounders, the ORs of obesity for short and long sleep durations relative to normal sleep duration were 1.31 (95% CI 1.01, 1.76) and 1.64 (95% CI 1.04, 2.61) (P < 0.05), respectively. No significant association was observed between sleep duration and overweight risk. Sleep duration was significantly associated with BMI in the participants aged <45 years (P < 0.05). In particular, BMI was significantly higher in the par-
3 ticipants who slept for a long duration than in those who slept for a normal duration. No significant difference was observed in BMI distributed according to sleep duration in the participants aged ≥45 years (Fig. 1).
Discussion Our study results revealed a both short and long sleep duration association with obesity risk in adults, consistent with the results of previous studies [4,23]. However, no significant association of sleep duration with overweight was observed. Studies have indicated that the shortening of sleep duration by 1 h increases BMI by 0.35 units [24] to 0.42 units [25]. For a 170-cm tall adult, the shortening of sleep duration by 1 h increases total body weight by approximately 1.01—1.21 kg. Although the magnitude of weight gain is not substantial, a slight but persistent change in sleep duration may negatively affect body weight, which should not be overlooked [26]. Obesity is caused by the interaction of complex multiple risk factors. The pathogenesis of obesity is complicated; thus, investigating the contribution of only a single risk factor to obesity is difficult. A study indicated that 3—5% of obesity in adults can be attributed to short sleep duration, highlighting the crucial role of inadequate sleep in the prevalence of obesity [27]. The physiological mechanism underlying the association of sleep duration with obesity remains unclear, and inferences from previous studies may provide some explanation. First, the shortening of sleep duration is associated with appetiteregulating hormone changes, which can increase the appetite and food intake, leading to weight gain [28]. Second, a short sleep duration increases fatigue or reduces activity during the daytime, which results in more sedentary time without adequate energy expenditure, thus negatively affecting weight stability [29]. Third, studies have indicated that a decrease in sleep duration is often accompanied by irregular eating habits and increased caloric intake. In particular, the preferential intake of fat-containing, high-carbohydrate, and energy-dense food is significantly increased. Although the caloric intake is increased, the daytime energy expenditure remains unchanged; leading to weight gain [30]. These biological evidence could convince us the current findings that short sleep time association with abnormal weight. Sleep has a major role in the regulation of glucose metabolism and neuroendocrine function in adults. Sleep deprivation is associated with
Please cite this article in press as: Lin C-L, et al. The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study. Obes Res Clin Pract (2016), http://dx.doi.org/10.1016/j.orcp.2016.07.005
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C.-L. Lin et al. Table 1
Characteristics of the study participants (n = 1548).
Characteristic
No. of individuals (%) Age, mean ± SD <45 years (no., %) ≥45 years (no., %) Female (no., %) FPG, mean ± SD TC, mean ± SD WC, mean ± SD BMI, mean ± SD Hypertension (no., %) DM (no., %) BW category Normal (no., %) Overweight (no., %) Obesity (no., %)
Sleep duration, h ≤6 h (g1)
>6 to <9 h (g2)
≥9 h (g3)
449 (29) 46.0 ± 11.2 172 (23.1) 277 (34.5) 228 (28.2) 111.2 ± 39.8 192.3 ± 39.4 82.5 ± 11.1 24.7 ± 4.2 87 (37.3) 62 (43.1)
962 (62.2) 42.2 ± 11.8 494 (66.4) 468 (58.2) 499 (61.7) 104.1 ± 28.4 187.0 ± 33.3 80.7 ± 10.5 24.0 ± 3.9 122 (52.4) 70 (48.6)
137 (8.8) 41.0 ± 13.1 78 (10.5) 59 (7.3) 82 (10.1) 103.9 ± 26.0 186.5 ± 44.9 81.8 ± 10.5 24.8 ± 4.9 24 (10.3) 12 (8.3)
210 (26.8) 110 (27.0) 129 (36.0)
509 (65.0) 262 (64.4) 191 (53.4)
64 (8.2) 35 (8.6) 38 (10.6)
2 /F
Scheffe’s test
NA 17.44***
g1 > g2, g3
3.62 7.88** 3.58* 4.28* 6.02** 11.45** 15.53*** 15.44***
g1 > g2 g1 > g2 g1 > g2 g1 > g2
2 , Chi-square test was executed to test categorical variables between groups. F, One-way ANOVA (Scheffe’s test) was executed to test continuous variables among three groups. Abbreviations: FPG, fasting plasma glucose; TC, total cholesterol; WC, waist circumference; BMI, body mass index; DM, type 2 diabetes; BW, body weight; No, number of individuals; NA, data not applicable; g, group. * p < 0.05. ** p < 0.01. *** p < 0.001.
Table 2
Prognostic effects of the association of sleep duration with overweight and obesity. Model 1
Model 2
Model 3
SD
Overweight
Obesity
Overweight
Obesity
Overweight
Obesity
≤6 h
1.01 (0.77—1.33) 1 1.06 (0.68—1.64)
1.64** (1.24—2.16) 1 1.59* (1.09—2.65)
0.90 (0.68—1.19) 1 1.19 (0.76—1.88)
1.47* (1.11—1.94) 1 1.73* (1.11—2.71)
0.86 (0.64—1.15) 1 1.19 (0.75—1.88)
1.31* (1.01—1.76) 1 1.64* (1.04—2.61)
>6 to <9 h (reference) ≥9 h
Abbreviation: SD, sleep duration. Model 1: unadjusted OR and 95% CI. Model 2: adjusted for age and sex. Model 3: adjusted for age, sex, FPG, TC, WC, hypertension, and DM. * p < 0.05. ** p < 0.01.
chronic diseases [7,9] for example; both short and long sleep durations are markers of cardiovascular outcomes [31]. Another study indicated that the quantity and quality of sleep consistently and significantly increases the risk of type 2 diabetes [32]. Inadequate sleep duration can be regarded as a potentially modifiable risk factor [33,34]. When sleep duration increases from 2—4 to 6 h, BMI follows a decreasing trend; however, when sleep duration is >6 h, BMI remains unchanged [33]. In this study, sleep duration of ≥9 h per night was associated with an increased risk of obesity; this
result is consistent with those of previous studies [23,35]. However, we could not confirm the actual mechanism underlying this association. Nevertheless, studies have reported that sleep-disordered breathing, mental status, and medication side effects simultaneously increase sleep duration and obesity risk [20,33]. Health care workers should be vigilant regarding the high concurrence of long sleep duration with other health problems and should further evaluate the cause of long sleep duration to provide appropriate management.
Please cite this article in press as: Lin C-L, et al. The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study. Obes Res Clin Pract (2016), http://dx.doi.org/10.1016/j.orcp.2016.07.005
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Figure 1 Association of sleep duration with body mass index distribution among two age populations.
This study demonstrated that among participants aged <45 years, BMI was significantly higher in those who slept for a long duration than in those who slept for a normal duration. However, no significant association was observed between sleep duration and BMI in participants aged ≥45 years. A previous study suggested that the association of sleep duration with obesity weakens with increasing age [34]. The relationship between these two factors may relate to the aging process and sleep architecture changes. Hence, the association of sleep duration with obesity is mediated by the age effect [36]. Furthermore, obstructive sleep apnea (OSA) often occurs in the younger population and is a common cause of inadequate sleep in young adults. Because the association of OSA with obesity is high [11,37], we could not exclude the possibility that the association of sleep duration with obesity is affected by OSA in the young population. Ethnic differences have been associated with different sleep behaviors and sleep durations [38]. Patel and Hu inferred that ethnic differences may be associated with susceptibility to sleep loss, and affected both sleep and obesity [12,13]. In Asian population, Itani et al. demonstrated that short sleep duration increases the morbidity risk for obesity among Japanese working adults. In addition,
Ko et al. found obesity is associated with reduced sleep duration in men among Hong Kong population [15]. In the current study, both short and long sleep duration were associated with a higher prevalence of obesity among adults in Taiwan. Future studies are required to evaluate whether inadequate sleep duration increases obesity risk in various demographic populations, in conjunction with other modifiable risk factors such as diet pattern and exercise. Despite adjustment for confounding factors, some unmeasured or unknown biases may exist. Our study has several limitations. First, self-reported sleep duration might have a potential bias; thus, future research should use objective sleep measurements (e.g., a sleep log and actigraphy) to improve the validity of sleep duration data. Second, the cross-sectional study design could not establish a cause relationship between sleep duration and obesity. Third, because the participants were community-dwelling adults aged 19—64 years, the obtained results could not be generalised to other age populations such as children and older people. Fourth, obesity involves a complex combination of genetic, environmental, and lifestyle factors. A family history of obesity is considered a crucial risk factor for obesity. However, this information was
Please cite this article in press as: Lin C-L, et al. The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study. Obes Res Clin Pract (2016), http://dx.doi.org/10.1016/j.orcp.2016.07.005
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C.-L. Lin et al.
not available in our dataset; this limitation might have influenced our study results.
Conclusions In conclusion, sleep has a crucial role in the regulation of neuroendocrine function in adults. The study demonstrated that normal sleep duration has less risk of obesity than short or long sleep duration. Clinical practitioners should comprehensively assess whether novel risks related to obesity are overlooked. In addition to reducing conventional risks related to diet and exercise, paying more attention to sleep problems and abnormal weight gain risk is crucial.
Authors’ contributions Chia-Ling Lin and Yu-Hsia Tsai conceptualised and designed the study. All authors collected, assembled, analysed, and interpreted the data. All authors wrote and gave final approval to the manuscript.
Conflicts of interest None declared.
Acknowledgements The authors thank all the dedicated field workers involved in NAHSIT 2005—2008, and all the people who participated in the survey.
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Please cite this article in press as: Lin C-L, et al. The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study. Obes Res Clin Pract (2016), http://dx.doi.org/10.1016/j.orcp.2016.07.005
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Obesity Research & Clinical Practice (2016) xxx, xxx—xxx
ORIGINAL ARTICLE
The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study Chia-Ling Lin a, Chun-Ping Lin b, Shu-Wen Chen a, Hsueh-Ching Wu c, Yu-Hsia Tsai d,e,∗ a
Department of Nursing, Chang Gung University of Science and Technology, Taoyuan, Taiwan b Department of Nursing, Shu-Zen Junior College of Medicine and Management, Kaohsiung, Taiwan c Department of Nursing, Hsin Sheng College of Medical Care and Management, Taoyuan, Taiwan d Department of Nursing, College of Medicine, Chang Gung University, Taoyuan, Taiwan e Department of Cardiovascular Medicine, Chang Gung Memorial Hospital, Taoyuan, Taiwan Received 19 December 2015 ; received in revised form 20 July 2016; accepted 25 July 2016
KEYWORDS Sleep duration; Overweight; Obesity; Body mass index; Adults
Summary Background/objective: The effect of eating habits and sedentary lifestyle on obesity has been extensively examined and supported; however, few studies have examined the association of sleep duration with obesity in Taiwan. To redress this gap, this study investigated the association of sleep duration with overweight and obesity in community-dwelling Taiwanese adults. Methods: A cross-sectional study was performed using the 2005—2008 Nutrition and Health Survey in Taiwan (NAHSIT). A logistic regression model was used to calculate the odds ratios (ORs) and 95% confidence intervals (CIs) of the association of sleep duration with overweight and obesity. Nightly sleep duration was divided into three groups: >6 to <9 h (normal), ≤6 h (short), and ≥9 h (long). Results: A total of 1548 adults aged 20—64 years were examined in this study. The adjusted ORs of obesity for short and long sleep duration relative to a normal sleep duration were 1.31 (95% CI 1.01, 1.76) and 1.64 (95% CI 1.04, 2.61), respectively. No significant association of sleep duration with overweight was observed.
∗ Corresponding author at: Department of Nursing, College of Medicine, Chang Gung University, Taoyuan, Taiwan; Department of Cardiovascular Medicine, Chang Gung Memorial Hospital, Taoyuan, Taiwan; No. 259, Wenhua 1st Rd., Guishan Dist., Taoyuan 33302, Taiwan. Tel.: +886 3 2118800 ext 5184. E-mail address: [email protected] (Y.-H. Tsai).
http://dx.doi.org/10.1016/j.orcp.2016.07.005 1871-403X/© 2016 Asia Oceania Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Lin C-L, et al. The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study. Obes Res Clin Pract (2016), http://dx.doi.org/10.1016/j.orcp.2016.07.005
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C.-L. Lin et al. Conclusions: The present study suggests that both short and long sleep duration are associated with obesity risk. © 2016 Asia Oceania Association for the Study of Obesity. Published by Elsevier Ltd. All rights reserved.
Introduction
Methods
Over the few decades, obesity has become a common epidemic disease [1]. Evidence has indicated that obesity negatively affects health outcomes and increases health care costs. Moreover, obesity prevention has become a critical health concern and has been addressed in several countries [2]. A study reported that obesity results from complex multifactorial interactions, such as those involving genes, eating habits, sedentary lifestyle, and environment [3]. Studies have reported an association of short sleep duration with obesity risk [4—6]. Moreover, experimental studies have indicated that a decrease in sleep duration is associated with changes in orexins, including increased ghrelin and decreased leptin [7—9]. By contrast, other studies have reported that no significant association of sleep duration with body mass index (BMI) [10,11]. This contradiction indicates the necessity of further research to verify the relationship between these two factors. Prior study indicated that the association of sleep duration with obesity may be affected by racial disparities [12]. For instance, African Americans are more susceptible to the curtailment of sleep duration and have a higher risk of obesity than Caucasians [13]. Compared to the Western society or other Asian countries, both sleep duration and obesity have been extensively surveyed [4—6,14,15]. In Taiwan, one study reported that adolescents who frequently obtained 6—8 h per night had a decreased probability of becoming overweight [16]. In addition, the paucity of studies addresses the correlation between sleep duration and weight abnormality in Taiwanese adults. Therefore, this study investigated the association of varying sleep durations with overweight and obesity in Taiwanese adults aged 20—64 years based on the 2005—2008 Nutrition and Health Survey in Taiwan (NAHSIT).
Data sources We performed a secondary database analysis using data from the 2005—2008 NAHSIT a populationbased cross-sectional study performed using a stratified multistage cluster sampling method. The details of the sampling method have been reported in previous studies [17,18].
Inclusion criteria for participation The study population included community-dwelling adults aged 20—64 years who participated in the 2005—2008 NAHSIT. In total, 1548 participants who completed both the physical examination and questionnaire form were included in the current analysis.
Definitions of sleep duration, overweight, obesity, waist circumference, hypertension, and type 2 diabetes The participants described their sleep duration during weeknights (Sunday—Thursday) and weekends (Friday and Saturday) in the previous week. We used the following formula described by Hall et al. to determine sleep duration: ((5 × weekday standard deviation (SD)) + (2 × weekend (SD))/7) [19]. Furthermore, we divided nightly sleep duration into the following three groups according to a previous study [20]: short (≤6 h per night), normal (>6 to <9 h per night), and long (≥9 h per night). Overweight/obesity: BMI was calculated as weight (kg) divided by height (m2 ) [21]. Height and weight were measured to the nearest 0.1 cm and 0.1 kg, respectively [18]. Overweight and obesity were defined as BMI 24—26.9 and BMI ≥ 27, respectively, in accordance with criteria for Taiwanese adults defined by the Ministry of Health and
Please cite this article in press as: Lin C-L, et al. The association between sleep duration and overweight or obesity in Taiwanese adults: A cross-sectional study. Obes Res Clin Pract (2016), http://dx.doi.org/10.1016/j.orcp.2016.07.005
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Sleep duration and overweight or obesity Welfare, Taiwan. Waist circumference (WC): WC was measured at the midpoint between the lower border of the rib cage and the top of the iliac crest [22]. Hypertension was defined on the basis of the selfreported previous history of hypertension or the present use of antihypertensive drugs. Type 2 diabetes was defined on the basis of the participants’ fasting plasma glucose level of ≥126 mg/dL or the present use of antidiabetic drugs.
Ethical approval This study was approved by the Research Ethics Committee of National Taiwan University Hospital (201503123W).
Statistical analysis All statistical analyses were performed using the SPSS software (Version 21; SPSS Inc., Chicago, IL, USA). For descriptive statistics, basic information was expressed as percentages, means, and SDs. For inferential statistics, a one-way ANOVA was performed to examine the distribution and difference of continuous variables with varying SDs. The Chi-square test was used to calculate the odds ratio (OR) and 95% confidence interval (CI) of the dependent variable for each independent variable. Furthermore, a multiple logistic regression was used to calculate the OR value of the dependent variable in the multivariate analysis after adjustment for confounders. A significance level of ˛ = 0.05 was used.
Results In total, we included 1548 adults aged 20—64 years (739 men and 809 women), with average age of 43.5 years (SD = 12.1). The proportion of women was higher than that of men and accounted for more than half of the participants. The mean BMI of the participants was 24.4 kg/m2 (SD = 4.1), and the mean sleep duration was 7.0 h (SD = 1.3) (Table 1). Table 2 shows that after adjustment for confounders, the ORs of obesity for short and long sleep durations relative to normal sleep duration were 1.31 (95% CI 1.01, 1.76) and 1.64 (95% CI 1.04, 2.61) (P < 0.05), respectively. No significant association was observed between sleep duration and overweight risk. Sleep duration was significantly associated with BMI in the participants aged <45 years (P < 0.05). In particular, BMI was significantly higher in the par-
3 ticipants who slept for a long duration than in those who slept for a normal duration. No significant difference was observed in BMI distributed according to sleep duration in the participants aged ≥45 years (Fig. 1).
Discussion Our study results revealed a both short and long sleep duration association with obesity risk in adults, consistent with the results of previous studies [4,23]. However, no significant association of sleep duration with overweight was observed. Studies have indicated that the shortening of sleep duration by 1 h increases BMI by 0.35 units [24] to 0.42 units [25]. For a 170-cm tall adult, the shortening of sleep duration by 1 h increases total body weight by approximately 1.01—1.21 kg. Although the magnitude of weight gain is not substantial, a slight but persistent change in sleep duration may negatively affect body weight, which should not be overlooked [26]. Obesity is caused by the interaction of complex multiple risk factors. The pathogenesis of obesity is complicated; thus, investigating the contribution of only a single risk factor to obesity is difficult. A study indicated that 3—5% of obesity in adults can be attributed to short sleep duration, highlighting the crucial role of inadequate sleep in the prevalence of obesity [27]. The physiological mechanism underlying the association of sleep duration with obesity remains unclear, and inferences from previous studies may provide some explanation. First, the shortening of sleep duration is associated with appetiteregulating hormone changes, which can increase the appetite and food intake, leading to weight gain [28]. Second, a short sleep duration increases fatigue or reduces activity during the daytime, which results in more sedentary time without adequate energy expenditure, thus negatively affecting weight stability [29]. Third, studies have indicated that a decrease in sleep duration is often accompanied by irregular eating habits and increased caloric intake. In particular, the preferential intake of fat-containing, high-carbohydrate, and energy-dense food is significantly increased. Although the caloric intake is increased, the daytime energy expenditure remains unchanged; leading to weight gain [30]. These biological evidence could convince us the current findings that short sleep time association with abnormal weight. Sleep has a major role in the regulation of glucose metabolism and neuroendocrine function in adults. Sleep deprivation is associated with
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C.-L. Lin et al. Table 1
Characteristics of the study participants (n = 1548).
Characteristic
No. of individuals (%) Age, mean ± SD <45 years (no., %) ≥45 years (no., %) Female (no., %) FPG, mean ± SD TC, mean ± SD WC, mean ± SD BMI, mean ± SD Hypertension (no., %) DM (no., %) BW category Normal (no., %) Overweight (no., %) Obesity (no., %)
Sleep duration, h ≤6 h (g1)
>6 to <9 h (g2)
≥9 h (g3)
449 (29) 46.0 ± 11.2 172 (23.1) 277 (34.5) 228 (28.2) 111.2 ± 39.8 192.3 ± 39.4 82.5 ± 11.1 24.7 ± 4.2 87 (37.3) 62 (43.1)
962 (62.2) 42.2 ± 11.8 494 (66.4) 468 (58.2) 499 (61.7) 104.1 ± 28.4 187.0 ± 33.3 80.7 ± 10.5 24.0 ± 3.9 122 (52.4) 70 (48.6)
137 (8.8) 41.0 ± 13.1 78 (10.5) 59 (7.3) 82 (10.1) 103.9 ± 26.0 186.5 ± 44.9 81.8 ± 10.5 24.8 ± 4.9 24 (10.3) 12 (8.3)
210 (26.8) 110 (27.0) 129 (36.0)
509 (65.0) 262 (64.4) 191 (53.4)
64 (8.2) 35 (8.6) 38 (10.6)
2 /F
Scheffe’s test
NA 17.44***
g1 > g2, g3
3.62 7.88** 3.58* 4.28* 6.02** 11.45** 15.53*** 15.44***
g1 > g2 g1 > g2 g1 > g2 g1 > g2
2 , Chi-square test was executed to test categorical variables between groups. F, One-way ANOVA (Scheffe’s test) was executed to test continuous variables among three groups. Abbreviations: FPG, fasting plasma glucose; TC, total cholesterol; WC, waist circumference; BMI, body mass index; DM, type 2 diabetes; BW, body weight; No, number of individuals; NA, data not applicable; g, group. * p < 0.05. ** p < 0.01. *** p < 0.001.
Table 2
Prognostic effects of the association of sleep duration with overweight and obesity. Model 1
Model 2
Model 3
SD
Overweight
Obesity
Overweight
Obesity
Overweight
Obesity
≤6 h
1.01 (0.77—1.33) 1 1.06 (0.68—1.64)
1.64** (1.24—2.16) 1 1.59* (1.09—2.65)
0.90 (0.68—1.19) 1 1.19 (0.76—1.88)
1.47* (1.11—1.94) 1 1.73* (1.11—2.71)
0.86 (0.64—1.15) 1 1.19 (0.75—1.88)
1.31* (1.01—1.76) 1 1.64* (1.04—2.61)
>6 to <9 h (reference) ≥9 h
Abbreviation: SD, sleep duration. Model 1: unadjusted OR and 95% CI. Model 2: adjusted for age and sex. Model 3: adjusted for age, sex, FPG, TC, WC, hypertension, and DM. * p < 0.05. ** p < 0.01.
chronic diseases [7,9] for example; both short and long sleep durations are markers of cardiovascular outcomes [31]. Another study indicated that the quantity and quality of sleep consistently and significantly increases the risk of type 2 diabetes [32]. Inadequate sleep duration can be regarded as a potentially modifiable risk factor [33,34]. When sleep duration increases from 2—4 to 6 h, BMI follows a decreasing trend; however, when sleep duration is >6 h, BMI remains unchanged [33]. In this study, sleep duration of ≥9 h per night was associated with an increased risk of obesity; this
result is consistent with those of previous studies [23,35]. However, we could not confirm the actual mechanism underlying this association. Nevertheless, studies have reported that sleep-disordered breathing, mental status, and medication side effects simultaneously increase sleep duration and obesity risk [20,33]. Health care workers should be vigilant regarding the high concurrence of long sleep duration with other health problems and should further evaluate the cause of long sleep duration to provide appropriate management.
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Figure 1 Association of sleep duration with body mass index distribution among two age populations.
This study demonstrated that among participants aged <45 years, BMI was significantly higher in those who slept for a long duration than in those who slept for a normal duration. However, no significant association was observed between sleep duration and BMI in participants aged ≥45 years. A previous study suggested that the association of sleep duration with obesity weakens with increasing age [34]. The relationship between these two factors may relate to the aging process and sleep architecture changes. Hence, the association of sleep duration with obesity is mediated by the age effect [36]. Furthermore, obstructive sleep apnea (OSA) often occurs in the younger population and is a common cause of inadequate sleep in young adults. Because the association of OSA with obesity is high [11,37], we could not exclude the possibility that the association of sleep duration with obesity is affected by OSA in the young population. Ethnic differences have been associated with different sleep behaviors and sleep durations [38]. Patel and Hu inferred that ethnic differences may be associated with susceptibility to sleep loss, and affected both sleep and obesity [12,13]. In Asian population, Itani et al. demonstrated that short sleep duration increases the morbidity risk for obesity among Japanese working adults. In addition,
Ko et al. found obesity is associated with reduced sleep duration in men among Hong Kong population [15]. In the current study, both short and long sleep duration were associated with a higher prevalence of obesity among adults in Taiwan. Future studies are required to evaluate whether inadequate sleep duration increases obesity risk in various demographic populations, in conjunction with other modifiable risk factors such as diet pattern and exercise. Despite adjustment for confounding factors, some unmeasured or unknown biases may exist. Our study has several limitations. First, self-reported sleep duration might have a potential bias; thus, future research should use objective sleep measurements (e.g., a sleep log and actigraphy) to improve the validity of sleep duration data. Second, the cross-sectional study design could not establish a cause relationship between sleep duration and obesity. Third, because the participants were community-dwelling adults aged 19—64 years, the obtained results could not be generalised to other age populations such as children and older people. Fourth, obesity involves a complex combination of genetic, environmental, and lifestyle factors. A family history of obesity is considered a crucial risk factor for obesity. However, this information was
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not available in our dataset; this limitation might have influenced our study results.
Conclusions In conclusion, sleep has a crucial role in the regulation of neuroendocrine function in adults. The study demonstrated that normal sleep duration has less risk of obesity than short or long sleep duration. Clinical practitioners should comprehensively assess whether novel risks related to obesity are overlooked. In addition to reducing conventional risks related to diet and exercise, paying more attention to sleep problems and abnormal weight gain risk is crucial.
Authors’ contributions Chia-Ling Lin and Yu-Hsia Tsai conceptualised and designed the study. All authors collected, assembled, analysed, and interpreted the data. All authors wrote and gave final approval to the manuscript.
Conflicts of interest None declared.
Acknowledgements The authors thank all the dedicated field workers involved in NAHSIT 2005—2008, and all the people who participated in the survey.
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