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Table 1 Baseline characteristics of the study participants according to difficulty initiating sleep categories, 1999–2004, HIPOP-OHP, Japan

From: Relation between sleep quality and quantity, quality of life, and risk of developing diabetes in healthy workers in Japan: the High-risk and Population Strategy for Occupational Health Promotion (HIPOP-OHP) Study

  Difficulty initiating sleeping
  Non Sometimes Often
No. of subjects (%) 3993 (61.3) 1996 (30.7) 520 (8.0)
Age * 38.4 ± 9.5 38.3 ± 9.5 36.2 ± 9.5
Gender (male, %) 77.7 78.6 83.0
BMI (kg/m2) † ‡ 22.7 ± 0.05 22.7 ± 0.07 22.8 ± 0.14
Physical activity (MET-h/week) † § 5.5 ± 0.17 4.3 ± 0.24 5.1 ± 0.46
History of hypercholesterolemia (%) 7.5 7.8 8.4
History of hypertension (%) 11.8 13.1 13.6
Smoking (%)    
   Never 44.4 37.1 30.0
   Past 15.9 12.6 14.1
   Current 39.7 50.3 55.9
Family history of diabetes (%) 18.2 19.1 17.8
Sleeping time (hours) (%)    
   <6 14.3 16.9 30.3
   6–7 41.9 44.6 42.4
   7–8 34.3 31.6 21.9
   8< 9.5 6.9 5.4
Alcohol intake quartiles (%)    
   1Q (0 mg/week) 44.2 44.6 46.0
   2Q (0.1–2.5 mg/week) 1.4 1.2 1.0
   3Q (2.6–25.0 mg/week) 23.8 23.1 19.0
   4Q (25.1-mg/week) 22.2 21.0 24.5
   Data missing 8.4 10.1 9.5
  1. * Plus-minus values are means ± SD
  2. † Plus-minus values are means ± SE
  3. ‡ BMI denotes body mass index
  4. § MET-h denotes metabolic equivalent hours