Elsevier

Sleep Medicine

Volume 14, Issue 10, October 2013, Pages 950-954
Sleep Medicine

Original Article
Longer 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

https://doi.org/10.1016/j.sleep.2013.04.015Get rights and content

Abstract

Objectives

Afternoon napping is a common habit in China. We used data obtained from the Dongfeng–Tongji cohort to examine if duration of habitual afternoon napping was associated with risks for impaired fasting plasma glucose (IFG) and diabetes mellitus (DM) in a Chinese elderly population.

Methods

A total of 27,009 participants underwent a physical examination, laboratory tests, and face-to-face interview. They were categorized into four groups according to nap duration (no napping, <30, 30 to <60, 60 to <90, and ⩾90 min). Logistic regression models were used to examine the odds ratios (ORs) of napping duration with IFG and DM.

Results

Of the participants, 18,515 (68.6%) reported regularly taking afternoon naps. Those with longer nap duration had considerably higher prevalence of IFG and DM. Napping duration was associated in a dose-dependent manner with IFG and DM (P < .001). After adjusting for possible confounders, longer nap duration (>60 min; all P < .05) was still significantly associated with increased risk for IFG, and longer nap duration (>30 min) was associated with increased risk for DM; however, this finding was not significant in the group with a nap duration of 60–90 min.

Conclusions

Longer habitual afternoon napping was associated with a moderate increase for DM risk, independent of several covariates. This finding suggests that longer nap duration may represent a novel risk factor for DM and higher blood glucose levels.

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.

Section snippets

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.

. ICMJE Form for Disclosure of Potential Conflicts of Interest form.

Acknowledgments

We thank the Dongfeng–Tongji cohort participants and the staff at Dongfeng Motor Corporation in Dongfeng General Hospital for the data collection.

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