Age-dependent changes in the association between sleep duration and impaired glucose metabolism

Table 1 Characteristics of younger subjects classified by sleep duration

Sleep duration	≤ 5 h	6 h	7 h	≥ 8 h	P values
n (%)	4110 (12.5)	16265 (49.4)	9377 (28.5)	3177 (9.6)
Male, n (%)	2865 (69.7)	11121 (68.4)	6349 (67.7)	2026 (63.8)	< 0.0001
Age (yr)	30.5 ± 5.5	30.4 ± 5.3	30.7 ± 5.3	31.1 ± 5.3	< 0.0001
BMI (kg/m2)	23.4 ± 3.9	23.1 ± 3.7	22.8 ± 3.6	23.0 ± 3.8	< 0.0001
Systolic blood pressure (mmHg)	118 ± 14.3	118 ± 14.5	118 ± 14.6	119 ± 14.8	0.58
White blood cell count (× 109/L)	6.67 ± 1.8	6.48 ± 1.7	6.46 ± 1.7	6.48 ± 1.9	< 0.0001
Serum triglycerides (mmol/L)	0.9 (0.6-1.5)	0.9 (0.6-1.4)	0.9 (0.6-1.5)	0.9 (0.6-1.5)	0.46
Serum HDL-cholesterol (mmol/L)	1.6 ± 0.4	1.6 ± 0.4	1.6 ± 0.4	1.6 ± 0.4	0.04
HbA1c (NGSP, %)	5.35 ± 0.5	5.32 ± 0.5	5.30 ± 0.4	5.29 ± 0.5	< 0.0001
Work duration (h/d)	9.4 ± 1.5	9.0 ± 1.4	8.6 ± 1.3	8.1 ± 1.4	< 0.0001
Pharmacotherapy for
Hypertension, n (%)	25 (0.6)	73 (0.4)	38 (0.4)	19 (0.6)	0.29
Diabetes, n (%)	13 (0.3)	39 (0.2)	22 (0.2)	11 (0.3)	0.83
Dyslipidemia, n (%)	11 (0.3)	46 (0.3)	24 (0.3)	22 (0.7)	0.0001
Current smokers, n (%)	1791 (43.6)	5980 (36.8)	3221 (34.4)	964 (30.3)	< 0.0001
Everyday alcohol consumers, n (%)	353 (8.6)	1386 (8.5)	1022 (10.9)	370 (11.6)	< 0.0001
Regular exercisers, n (%)1	553 (14.4)	3154 (17.2)	2740 (19.4)	1367 (21.8)	< 0.0001
Past history of
CVD, n (%)	46 (1.1)	129 (0.8)	102 (1.1)	46 (1.4)	0.002

Data are presented as mean ± SD, median (interquartile range), or n (%). P values were determined by ANOVA and χ² tests were used for continuous and categorical variables. Serum triglyceride concentrations were log transformed before parametric analysis.

¹Regular exercise was defined as ≥ 30 min exercise per session at least twice a week. Values of white blood cell count are only available in 32713 subjects (n = 4073, 16171, 9313, and 3156, for ≤ 5 h, 6 h, 7 h, and ≥ 8 h sleep duration, respectively). BMI: Body mass index; HDL: High-density lipoprotein; NGSP: National Glycohemoglobin Standardization Program; CVD: Cardiovascular disease.