Table 1. Summary of cohort studies evaluating the association between napping and type 2 diabetes.
| Author, year of publication | Study participants location, subject source, and response rate | Assessment of exposure | Analysis by sex | Prevalence of napping (EDS) (%) |
|---|---|---|---|---|
| Diabetes and Daytime Napping | ||||
| Stang et al.15 a | Total = 4,458; diabetes = 355 (8.0%); 52% female; age 45–75 years; BMI not available; Germany; Participants were local residents of industrial cities in the Ruhr region of Germany. The response rate was 56%. | Structured interview | Yes | Male 17%, female 15% |
| Xu et al.16 b | Total = 174,020; diabetes = 10,100 (5.8%); 43% female; age 62.4 years; BMI 26.5 kg/m2; USA; Participants were members of the American Association of Retired Persons from six states and two metropolitan areas of the USA. The response rate was 56%. | Self-completed questionnaire | No | 46% |
| Fang et al.17 c | Total = 27,009; diabetes = 4,772 (17.7%); 55% female; age 63.6 years; BMI 24.5 kg/m2; China; Participants were retired employees of Dongfeng Motor Corporation, an automobile manufacturer in China. The response rate was 87%. | Self-completed questionnaire | No | 69% |
| Lam et al.18 d | Total = 19,567 (subsample 3.822); diabetes = 2,642 (13.5%); 71% female; age 62.2 years; BMI not available; China; Participants were members of the Guangzhou Health and Happiness Association for Respectable Elders, a community social and welfare association. The response rate was 90% for men and 99% for women. | Structured interview | No | 67% |
| Diabetes and Excessive Daytime Sleepiness | ||||
| Lindberg et al.21 e,f | Total = 6,779; diabetes = not available; 100% female; age 44.7 years; BMI 24.1 kg/m2; Sweden; Participants were a random sample of women living in the city of Uppsala, Sweden, drawn from the population registry. The response rate was 68.9%. | Self-completed questionnaire | No (female only) | 13% |
| Bixer et al.22 g | Total = 16,583; diabetes = 2,156 (13%); 74% female; age 46.5 years; BMI 26.3 kg/m2; Spain; Participants were a random sample of 16,583 men and women from central Pennsylvania. The response rate was 73.5% (men) and 74.1% (women). | Structured interview | No | 8.7% |
| Renko et al.23 h | Total = 593; diabetes = 84 (14.3%); 59% female; age 60 years; BMI not available; Finland; Participants were living in the City of Oulu in northern Finland. The response rate was 71%. | Self-completed questionnaire | No | 19.6% |
| Asplund.24 i | Total = 6,143; diabetes = not available; 61% female; age 73 years; BMI not available; Sweden; Participants were members of the National Swedish Pensioners’ Association. The response rate was 61%. | Self-completed questionnaire | Yes | Male 14%, female 14% |
| Metabolic Syndrome and Daytime Napping | ||||
| Wu et al.19 j | Total = 25,184; metabolic syndrome = 8,046 (31.9%); 55% female; age 63.6 years; BMI 25.8 kg/m2; China; Participants were retired employees of Dongfeng Motor Corporation in Shiyan City, Hubei Province, China. The response rate was 87%. | Self-completed questionnaire | Yes | Male 73%, female 65% |
| Lin et al.20 k | Total = 8,547; metabolic syndrome = 3,176 (37.2%); 28.2% female; age 56.0 years; BMI 23.7 kg/m2; China; Participants were from a community in Guangzhou, China. The response rate was 98.1%. | Self-completed questionnaire | Yes | Male 56%, female 48% |
Among these studies, one study (16) was a cohort study with a mean follow-up period of 7–10 years. All of the other studies were cross-sectional studies.
aAnalysis was adjusted for age, hypertension, smoking status, dyslipidemia, BMI, waist circumstance, CRP, Agatston score, and ABI.
bAnalysis was adjusted for age, sex, race, education, marital status, smoking, coffee and alcohol consumption, calorie intake, family history of diabetes, general health status, nocturnal sleep duration, physical activity, and BMI.
cAnalysis was adjusted for age, sex, marriage, education, smoking status, alcohol intake, hypertension, coronary heart disease, stroke, nocturnal sleep duration, BMI, and physical activity.
dAnalysis was adjusted for age, sex, educational level, occupation, smoking, alcohol intake, physical activity, health status (self-rated health, hospitalization, hypertension, cardiovascular disease, and family history of diabetes), adiposity and metabolic markers (waist circumference, triglycerides, and total cholesterol), and sleep variables (total sleep duration, insomnia, daytime sleepiness, and snoring). The estimate for the relation between a short nap time and diabetes was calculated from a subsample (n = 3,822) of the much larger study population (n = 19,567).
eAnalysis was stratified by presence of snoring.
fAnalysis was adjusted for age, BMI, alcohol dependency, level of physical activity, and smoking status.
gAnalysis was adjusted for age, sex, BMI, depression, smoking, alcohol use, allergy, asthma, hypertension, thyroid function, night time sleep duration, and objective polysomnographic data.
hAnalysis was adjusted for sex, depression, use of sleeping medication, smoking, and BMI.
iAnalysis was adjusted for age, general health, frequent awakening, ability to fall asleep again after nocturnal awakening, and hypnotic medication.
jAnalysis was adjusted for age, marriage, education, smoking status, drinking status, physical activity, coronary heart disease, myocardial infarction, stroke, family history of hypertension and diabetes, BMI, and nighttime sleep duration.
kAnalysis was adjusted for age, BMI, current smoking, drinking status, physical activity, and sleeping hours (total nocturnal sleeping hours).