Original ArticleLonger habitual afternoon napping is associated with a higher risk for impaired fasting plasma glucose and diabetes mellitus in older adults: results from the Dongfeng–Tongji cohort of retired workers
Introduction
Diabetes mellitus (DM) is a critical public health concern in both developing and developed countries. It is closely related to premature mortality and hospitalization for conditions such as cardiovascular and kidney disease [1]. Besides traditional lifestyle risk factors such as high-calorie diets and sedentary behavior, other nontraditional behavioral and environmental factors may contribute to the DM epidemic. Recent studies have revealed a U-shaped relationship between nocturnal sleep duration and DM, with both short and long sleep durations being significantly associated with the disease [2], [3], [4], [5], [6]. Xu et al. [7] reported that the risk for incident DM was not only associated with short nighttime sleeping but also with daytime napping.
Afternoon napping or the “siesta” is a common practice in many parts of the world, particularly in many Mediterranean and Latin American countries. A significant proportion of older adults report napping and the prevalence of napping increases with age [8]. Afternoon napping also is a popular habit in China, especially among older adults, and is regarded as a healthy habit in their culture. The prevalence of habitual afternoon napping among Chinese individuals ages 60 or older has been reported as 61.7% in men and 46.8% in women [9]. However, the health consequences of napping are poorly understood. Some studies have demonstrated that daytime napping is associated with a higher risk for all-cause mortality among older adults, with mortality associated with cardiovascular or cerebrovascular morbidity [10], [11], [12], [13], [14], [15]. Recent studies have reported that daytime napping is a risk factor for DM. A few epidemiologic studies, summarized in Table 1, have explored the relationship between daytime napping and DM [7], [16], [17], [18]. Evidence from the Guangzhou Biobank cohort suggested that frequency of napping was positively associated with an increased risk for type 2 DM among residents aged 50 years or older in southern China [16].
Previous studies on the association between napping and DM have not distinguished between napping caused by poor nighttime sleep resulting daytime sleepiness compared with napping as a regular routine practice. In the Chinese context, most elderly individuals take afternoon naps as a habit and as part of a lifestyle to promote better health. Given the high prevalence of DM and habitual afternoon napping among the elderly Chinese population, we sought to investigate habitual afternoon napping using data from the Dongfeng–Tongji cohort, evaluating the duration of habitual afternoon napping and the risk for DM.
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Study participants
Our research was conducted from the Dongfeng–Tongji cohort of retired workers, which collaborated between Tongji Medical College, Huazhong University of Science and Technology, and Dongfeng Motor Corporation (DMC). The DMC was founded in 1969 and is one of the three largest automobile manufacturers in China. The rationale, design, and methods of the Dongfeng–Tongji cohort have previously been described in detail [19]. Briefly, 87% (27,009/31,000) of retired employees older than 45 years (mean
Results
Of the 27,009 participants, 18,515 older adults (68.6%) reported regularly taking afternoon naps. The average duration of naps was 46 min for the nappers. Table 2 presents the characteristics of the study participants according to whether or not they took naps. Compared with the participants who reported no napping, nappers were more likely to report physician-diagnosed hypertension, coronary heart disease, DM, stroke, myocardial infarction, and hyperlipidemia. In addition more participants were
Discussion
In our cross-sectional study with a large sample size, we found that participants had a higher prevalence of habitual afternoon napping when compared with other studies [9], [16]. Longer habitual napping duration was associated with the risk for IFG and DM among this older Chinese population, while a shorter nap duration of less than 30 min had no impact on the risk for IFG and DM. After adjustment for possible confounders, including age, sex, marital status, education, chronic disease, alcohol
Funding sources
This research was funded by a grant support from National Natural Science Foundation of China, Project No. 81273083, and NECT Program 07-0333.
Conflict 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.2013.04.015.
Acknowledgments
We thank the Dongfeng–Tongji cohort participants and the staff at Dongfeng Motor Corporation in Dongfeng General Hospital for the data collection.
References (32)
- et al.
National, regional, and global trends in fasting plasma glucose and diabetes prevalence since 1980: systematic analysis of health examination surveys and epidemiological studies with 370 country-years and 2.7 million participants
Lancet
(2011) - et al.
Sleep duration as a risk factor for incident type 2 diabetes in a multiethnic cohort
Ann Epidemiol
(2009) - et al.
Frequent napping is associated with excessive daytime sleepiness, depression, pain, and nocturia in older adults: findings from the National Sleep Foundation ’2003 Sleep in America’ Poll
Am J Geriatr Psychiatry
(2007) - et al.
Sleep duration as a risk factor for the development of type 2 diabetes
Diabetes Care
(2006) - et al.
Sleep duration as a risk factor for diabetes incidence in a large U.S. sample
Sleep
(2007) - et al.
Role of sleep duration and quality in the risk and severity of type 2 diabetes mellitus
Arch Intern Med
(2006) - et al.
A prospective study of sleep duration and mortality risk in women
Sleep
(2004) - et al.
Day napping and short night sleeping are associated with higher risk of diabetes in older adults
Diabetes Care
(2010) - et al.
Sleep behavior of the urban elderly: a cross-sectional study
Chin J Behav Med Sci
(2002) - et al.
Daily siesta, cardiovascular risk factors, and measures of subclinical atherosclerosis: results of the Heinz Nixdorf Recall Study
Sleep
(2007)