Association between weight gain, obesity, and sleep duration: a large-scale 3-year cohort study
Previous research suggests that sleep duration is associated with obesity and weight gain. However, the majority of these studies are of cross-sectional design, with only a few cohort studies. In order to validate previous findings in a more real-world context, we evaluated the association between sleep duration, obesity, and weight gain in a large, 3-year cohort study.
A retrospective cohort study was conducted involving 21,469 apparently healthy individuals aged 20 years or older who underwent annual health check-ups at the Center for Preventive Medicine, St. Luke’s International Hospital, between 2005 and 2008. The participants were divided into four groups according to their self-reported average nightly sleep duration (≤5, 6, 7, and ≥8 h). We identified individuals with obesity (body mass index ≥25 kg/m2) and weight gain. Multivariate linear regression analysis and logistic regression analysis were used to explore the association between these variables and sleep duration, adjusting for age, gender, alcohol consumption, current smoking, past medical history, and level of physical activity.
Compared with those who slept 7 h, the individuals who slept ≤5 h night were more likely to experience weight gain (β coefficient = 0.03; 95% CI = 0.03–1.1) and to become obese (OR = 1.5; 95% CI = 1.1–2.0). No significant difference was seen between subjects who slept more than 8 h and those sleeping 7 h (OR = 1.3; 95% CI = 0.9–1.8).
Short sleep (≤5 h) is significantly associated with weight gain and obesity in both male and female adults.
KeywordsSleep duration Obesity Japan Weight gain Cohort
The prevalence of obesity is increasing worldwide, especially in developed countries . Prior to 1980, the prevalence was generally below 10% and has doubled or tripled in most of these countries. For example, in almost half of Organisation for Economic Co-operation and Development countries, 50% or more of the population is overweight . Although Japan was an exception in that the prevalence of obesity was only 3.4% in 2008, markedly lower than that of other developed countries, Japan was not immune to the gradual rise .
Obesity is associated with significant morbidity and mortality, most strongly in cardiovascular diseases. For example, it is associated with hypertension , diabetes , dyslipidemia  and coronary vascular disease [6, 7], and mortality . Therefore, preventing obesity is important for all developed countries.
Previous studies have shown an association between obesity and short sleep duration . However, most studies on sleep and weight are cross-sectional and thus are unable to determine causality . Only a few cohort studies were conducted in the past in limited populations such as male Japanese workers [11, 12] or young women .
Given the paucity of data, the association between obesity and sleep duration among men and women in the general adult population remains unclear. Our goal was to explore this association using a large sample of Japanese individuals who underwent annual health check-up over a 3-year period.
We consecutively enrolled all participants seen in the annual health check-up program between 2005 and 2008 at the Center for Preventive Medicine at St. Luke’s International Hospital in Tokyo, Japan. Attracting a large number of apparently healthy individuals, the purpose of this program is to promote public health through early detection of chronic diseases and their risk factors. In our center, around 80% of the participants is an employee of the various companies and local governmental organizations in Tokyo, as well as their dependents. Twenty percent of participants independently registered for the program. St. Luke’s International Hospital Ethics Committee institutional review board approved all aspects of this study.
Pre- and post-examination data were collected from adults (>20 years old) undergoing annual health check-up at our center. For linear analysis, we excluded obese individuals (BMI ≥25 kg/m2) at baseline. Two investigators independently extracted and recorded information using a structured format. A consensus was reached by discussion for any points of disagreement. To preserve patient confidentiality, direct patient identifiers were not collected in the process of creating the dataset.
Annual check-up consisted of self-reported demographic and lifestyle information (pre-exam questionnaire), medical history, initial evaluation (vital signs and laboratory data), and information about comorbidity (diabetes mellitus, hypertension, dyslipidemia) and past medical history (myocardial infarction, cerebral infarction), current medications, and any treatments received. Regular alcohol consumption was defined as drinking any amount of alcohol one or more times per week. Height and body weight were measured as part of annual check-up. Weight gain was defined as body mass index (BMI) increase from 2005 to 2008. In the questionnaire, participants reported their average duration of sleeping time per night at 2005, which was classified into four categories (≤5, 6, 7, and ≥8 h), as well as weekly frequency of physical activity. Based on the Japan Society for the Study of Obesity criteria, obesity was defined as BMI ≥25 kg/m2 , and the prevalence of obesity between 2005 and 2008 was compared for new diagnoses of obesity.
All analyses were conducted using SPSS 15.0J statistical software (SPSS Japan, Tokyo, Japan). Responses were analyzed using descriptive statistics, including mean, variance, standard deviation (SD), and percents. Chi-square or Fisher’s exact tests were used for cross-tabulated data and t tests were used to compare means of continuous data. Ninety-five percent confidence intervals (95% CI) were calculated using normal approximation methods.
Excluding obesity (BMI ≥25 kg/m2) participants in 2005, we constructed multivariate linear regression model for BMI change, calculating adjusted odds ratios (ORs) and 95% CIs. Logistic regression models were constructed to evaluate the adjusted associations between new diagnoses of obesity and duration of sleeping time.
Participants’ baseline characteristics (n = 21,469)
≤5 h (n = 5,045)
6 h (n = 8,678)
7 h (n = 5,658)
≥8 h (n = 2,088)
Total (n = 21,469)
Age, mean, y (SD)
Male, n (%)
Base line BMI
None per week
1–2 days per week
3–5 days per week
Almost all days
Alcohol drinker, n (%)
Past medical history
Weight and BMI change in 3 years (n = 13,820)
Weight change, kg (SD)
BMI change, kg/m2 (SD)
Results of Linear analysis about BMI change (n = 13,820) adjusted for age, gender, baseline BMI, alcohol drinking, exercise, hypertension, dyslipidemia, diabetes, cerebral infarction, and myocardial infarction
Results of logistic analysis about new obesity (n = 11,136) adjusted for age, gender, baseline BMI, alcohol drinking, exercise, hypertension, dyslipidemia, diabetes, cerebral infarction, and myocardial infarction
New obesity, n (%; n = 410)
In our study, short sleep duration was associated with weight gain and obesity over a 3-year period in both male and female apparently healthy adults. This association was held true after adjusting for traditional variables associated with obesity, including age, gender, alcohol consumption, frequency of exercise, hypertension, dyslipidemia, diabetes, cerebral infarction, and myocardial infarction. Those reporting less than 5 h of sleep per night tended to have more weight gain and more new-onset obesity compared with those reporting 7 h of sleep.
Previous cohort studies demonstrated the association between short sleep duration and weight gain and obesity, though these were conducted in limited populations, namely in the population of men  or young adult ; these findings are consistent with our results. Also the study in the population of different race and culture had similar result . From these facts, the relationship between sleep duration and obesity seems independent upon ethnicity and cultural habits.
Previous literature, including cross-sectional studies, has suggested physiologic pathways that include induced energy imbalance, hormonal abnormalities, and metabolic behavioral derangements such as increased hunger and reduced physical activity to explain this association .
In our study, there was no significant difference in weight gain or new-onset obesity between long sleep duration (more than 8 h) and 7 h sleep duration, but has tendency to weight gain or new-onset obesity. It suggests that long sleep also results in decreased weight/BMI, but perhaps not as strongly as 6–8 h sleep. Maybe sleep over 8 h is like a long tail of diminishing returns. There are some hypotheses about the association between long sleep duration and obesity from previous studies. First, the reduction of active time with longer sleep durations may reduce energy expenditure . Second, obstructive sleep apnea syndrome (OSAS), of which obesity is known to be a primary risk factor, was associated with long sleep duration. The production of proinflammatory cytokines, which cause sleepiness, is increased in OSAS patients. They may be a cause of this increased sleep duration . Third, high leptin resistance may cause obesity and weight gain . Individuals with long sleep durations have higher serum leptin levels, suggesting leptin resistance.
We also analyzed participants characteristics; for example, hypertension, diabetes, and dyslipidemia. The prevalence of those in our study was similar with that of Japanese population . In this aspect, our study was representative of the general Japanese population. However, because annual check-up needs payment, our participants might have high income or education status.
There are some limitations in our study. First, out of the 21,469 participants enrolled, even excluding participants with baseline obesity, only 13,820 participants were finally included in the linear regression analysis and logistic regression analysis due to missing data. Reformatting the health exam survey into a multiple choice questionnaire to facilitate patients’ ability to answer questions may be helpful . Second, we did not incorporate data on satisfaction or quality of sleep, nor timing of retiring or awakening, all of which may affect our results . Third, our study was retrospective; large-scale, prospective studies of sufficient duration are needed to further explore the association between sleep duration and obesity. In addition, our data did not include the data of potential confounders such as OSAS. However the prevalence in Japan is about 1%. Moreover those who have OSAS may be eliminated in baseline because of obesity. Therefore it might have small effects for our result.
Short sleep (≤5 h) may facilitate weight gain and the development of obesity in both male and female adults. Optimal sleep duration to mitigate weight gain in adults appears to be around 7 h.
We gratefully acknowledge Dr Toshiko Kawakita for contributing data of the Center for Preventive Medicine at St. Luke’s International Hospital.
Conflict of interest
- 1.Organisation for Economic Co-operation and Development.Obesity and the Economics of Prevention: Fit not Fat. Available at: http://www.oecd.org/document/31/0,3343,en_2649_33929_45999775_1_1_1_1,00.html Accessed Oct 2, 2010.
- 2.The Ministry of Health, Labour and Welfare in Japan. National health and Nutrition surveillance, 2004 Available at: http://www.mhlw.go.jp/houdou/2006/05/h0508-1a.html Accessed June 1, 2010.
- 14.Japan Society for the Study of Obesity. Determination of obesity and diagnostic ciriteria of adiposity. Available at: http://wwwsoc.nii.ac.jp/jasso/message/pdf/message_0901.pdf Accessed Oct 2, 2010.
- 16.Lyytikainen P, Rahkonen O, Lahelma E, Lallukka T.(2010) Association of sleep duration with weight and weight gain: a prospective follow-up study. J Sleep Res; 10.1111/j.1365-2869.Google Scholar
- 20.Japanese Ministry of Health, Labour and Welfare. Total number of patients in common disease 2005. Available at: http://www.mhlw.go.jp/toukei/saikin/hw/kanja/05/05.html Accessed Feb 28, 2011.