3-1. Background Factors
The characteristics of the subjects are shown in Table 1. The values of all cardiometabolic risk factors, except the serum HDL-C level, were significantly higher in the male than the female subjects. The mean age at menopause in the female subjects was 50.1 ± 4.1 years.
3-2. Relationship between Sleep Duration and Cardiometabolic Risk
Waist circumference
In the men with a sleep duration of <5 hours, ³5 hours, but less than 6 hours, ³6 hours, but less than 7 hours, ≥7 hours, but less than 8 hours, and ³8 hours per day, the WC values were 83.8 ± 9.64 cm, 83.5 ± 8.36 cm, 83.2 ± 8.37 cm, 82.8 ± 8.30 cm, and 84.1 ± 8.39 cm. In the women with a sleep duration of <5 hours, ³5 hours, but less than 6 hours, ³6 hours, but less than 7 hours, ≥7 hours, but less than 8 hours, and ³8 hours per day, 76.9 ± 11.5 cm, 75.9 ± 9.20 cm, 75.3 ± 8.53 cm, 75.2 ± 7.99 cm, and 75.1 ± 7.18 cm, respectively.
There tended to be a U-curve relationship between the WC and the sleep duration categories in the men (p = 0.079). In the women, the WC tended to increase as the sleep duration decreased (p = 0.072) (Figure 2).
Blood pressure
In the men with a sleep duration of <5 hours, ³5 hours, but less than 6 hours, ³6 hours, but less than 7 hours, ≥7 hours, but less than 8 hours, and ³8 hours per day, the systolic BP values were 118 ± 13.3 mmHg, 119 ± 14.3 mmHg, 119 ± 15.1 mmHg, 120 ± 15.3 mmHg, and 122 ± 14.3 mmHg, and the diastolic BP values were 72.6 ± 11.0 mmHg, 72.9 ± 12.0 mmHg, 73.0 ± 12.2 mmHg, 73.8 ± 12.1 mmHg, and 74.4 ± 10.8 mmHg, respectively. In the women with a sleep duration of <5 hours, ³5 hours, but less than 6 hours, ³6 hours, but less than 7 hours, ≥7 hours, but less than 8 hours, and ³8 hours per day, the systolic BP values were 108 ± 14.0 mmHg, 110 ± 14.3 mmHg, 109 ± 13.8 mmHg, 108 ± 14.4 mmHg, and 108 ± 12.7 mmHg, and the diastolic BP values were 64.7 ± 10.3 mmHg, 65.4 ± 10.7 mmHg, 65.3 ± 10.3 mmHg, 65.0 ± 10.5 mmHg, and 64.3 ± 9.6 mmHg, respectively.
In the men, the systolic BP increased significantly as the sleep duration increased (p <0.0001). Similarly, the diastolic BP also tended to increase as the sleep duration increased (p = 0.093). In the women, on the other hand, no association was observed between the sleep duration and the systolic/diastolic BP (Figure 2).
Lipid metabolism markers
In the men with a sleep duration of <5 hours, ³5 hours, but less than 6 hours, ³6 hours, but less than 7 hours, ≥7 hours, but less than 8 hours, and ³8 hours per day, the serum LDL-C levels were 124.8 ± 29.8 mg/dL, 121.5 ± 29.4 mg/dL, 119.9 ± 28.9 mg/dL, 120.7 ± 29.3 mg/dL, and 124.0 ± 30.7 mg/dL, the serum HDL-C levels were 55.9 ± 13.3 mg/dL, 56.1 ± 14.1 mg/dL, 56.7 ± 13.4 mg/dL, 57.1 ± 13.8 mg/dL, and 56.2 ± 13.2 mg/dL, the serum triglyceride levels were 89 (69/125) mg/dL, 90 (65/130) mg/dL, 94 (63/137) mg/dL, 91 (65/132) mg/dL, and 92 (67/134) mg/dL, and the serum non-HDL-C levels were 147.9 ± 32.9 mg/dL, 145.2 ± 32.6 mg/dL, 144.7 ± 32.8 mg/dL, 145.5 ± 33.2 mg/dL, and 148.6 ± 34.0 mg/dL, respectively. In the women with a sleep duration of <5 hours, ³5 hours, but less than 6 hours, ³6 hours, but less than 7 hours, ≥7 hours, but less than 8 hours, and ³8 hours per day, the serum LDL-C levels were 110.8 ± 30.5 mg/dL, 112.2 ± 30.3 mg/dL, 110.3 ± 29.5 mg/dL, 109.8 ± 30.7 mg/dL, and 105.2 ± 30.4 mg/dL, the serum HDL-C levels were 69.5 ± 15.9 mg/dL, 69.6 ± 13.9 mg/dL, 69.1 ± 14.2 mg/dL, 68.3 ± 14.0 mg/dL, and 66.7 ± 14.9 mg/dL, the serum triglyceride levels were 60 (45/83) mg/dL, 61 (46/84) mg/dL, 61 (46/84) mg/dL, 62 (46/87) mg/dL, and 64 (49/91) mg/dL, and the serum non-HDL-C levels were 131.5 ± 34.4 mg/dL, 132.3 ± 33.2 mg/dL, 130.8 ± 32.9 mg/dL, 130.7 ± 34.2 mg/dL, and 125.5 ± 33.2 mg/dL, respectively.
In the men, a U-curve relationship was observed between the serum LDL-C level and sleep duration and also between the serum non-HDL-C level and sleep duration, with a significant association between the sleep duration and the serum LDL-C level (p = 0.031). An inverted U-curve relationship was observed between the serum HDL-C level and sleep duration, but the association between the two variables was not significant. No significant association was found between the serum triglyceride level and sleep duration either. On the other hand, in the women, there was a significant inverted U-curve relationship between the serum LDL-C level and sleep duration (p = 0.011) and between the serum non-HDL-C level and sleep duration (p = 0.036). A significant inverted U-curve relationship was observed between the serum HDL-C levels and sleep duration (p = 0.016). However, no significant association was found between the serum triglyceride level and the sleep duration (Figure 2).
Glucose metabolism markers
In the men with a sleep duration of <5 hours, ³5 hours, but less than 6 hours, ³6 hours, but less than 7 hours, ≥7 hours, but less than 8 hours, and ³8 hours per day, the FBG levels were 98.0 ± 15.8 mg/dL, 96.6 ± 15.6 mg/dL, 96.5 ± 12.9 mg/dL, 96.2 ± 12.9 mg/dL, and 95.9 ± 10.9 mg/dL, and the HbA1c values were 5.70 ± 0.67 %, 5.65 ± 0.55 %, 5.62 ± 0.47 %, 5.61 ± 0.45 %, and 5.58 ± 0.39 %, respectively. In the women with a sleep duration of <5 hours, ³5 hours, but less than 6 hours, ³6 hours, but less than 7 hours, ≥7 hours, but less than 8 hours, and ³8 hours per day, the FBG levels were 91.6 ± 11.5 mg/dL, 90.4 ± 8.15 mg/dL, 89.9 ± 8.25 mg/dL, 89.0 ± 8.50 mg/dL, and 89.2 ± 7.36 mg/dL, and the HbA1c values were 5.63 ± 0.51 %, 5.60 ± 0.31 %, 5.56 ± 0.34 %, 5.53 ± 0.33 %, and 5.51 ± 0.31 %, respectively.
In the men, there was no significant association between the sleep duration and FBG. In the women, a significant U-curve relationship was found between the sleep duration and FBG (p <0.0001). In addition, the HbA1c increased significantly as the sleep duration decreased, in both the men and women (p = 0.016 in men, p <0.0001 in women) (Figure 2).
3-3. ORs and 95% CIs for Worsened Cardiometabolic Risk Factors by the Sleep Duration
As shown in Table 2, in the men, the values of the OR associated with a sleep duration of ³8 hours for WC ³reference value were 1.21 (95% CI, 0.96-1.51) and 1.16 (0.92-1.46) according to the analyses conducted using models 1 and 2, respectively, with no significant difference between the two values; however, the analysis conducted using model 3 yielded a significantly higher OR of (1.31 [1.004-1.71]) associated with a sleep duration of ³8 hours for WC ³reference value. The OR associated with a sleep duration of ³8 hours for systolic BP ³reference was significantly high in the analysis performed using model 1 (1.34 [1.03-1.74]); however, the statistically significant difference was no longer seen in the analysis performed using models 2 and 3. No significant association was found between the sleep duration and the diastolic BP. The values of OR associated with a sleep duration of <5 hours for serum LDL-C ³120 mg/dL were 1.43 (1.07-1.91) and 1.39 (1.02-1.89) according to the analysis performed using models 1 and 2, respectively, but the significant difference was no longer seen in the analysis using model 3. On the other hand, the OR associated with a sleep duration of ³8 h for LDL-C ³120 mg/dL was significantly high (1.27 [1.01-1.61]) in the analysis by model 3. The values of OR associated with a sleep duration ³8 h for serum non-HDL-C ³150 mg/dL were significantly high in the analysis by model 1 (1.30 [1.04-1.62]), model 2 (1.29 [1.02-1.62]), as well as model 3 (1.33 [1.05-1.68]). Furthermore, a significant OR for non-HDL-C ³150 mg/dL in association with a sleep duration of <5 h was found only in the analysis by model 2 (1.37 [1.01-1.85]). The OR for triglyceride ³150 mg/dL associated with a sleep duration of ³5, but <6 h was significantly low according to the analyses using all 3 models (model 1: 0.82 [0.68-0.996]; model 2: 0.79 [0.64-0.97]; model 3: 0.76 [0.61-0.94]). The OR for FBG of ³100 mg/dL associated with a sleep duration of <5 h was also significantly high as per the analyses conducted using all 3 models (model 1: 1.58 [1.18-2.14]; model 2: 1.77 [1.28-2.45]; model 3: 1.74 [1.25-2.42]).
On the other hand, in the women, as shown in Table 3, the OR for WC ³reference value associated with a sleep duration of <5 hours was significantly high as per analyses by all 3 models (model 1: 1.98 [1.25-3.14]; model 2: 2.26 [1.37-3.71]; model 3: 1.98 [1.11-3.55]). No significant association was noted between the sleep duration and BP. The OR for HDL-C <40 mg/dL associated with a sleep duration of ³5, but <6 hours was significantly low according to the analysis using model 1 (0.34 [0.12-0.98]), although no analyses using models 2 and 3 yielded no significant association. The OR for FBG ³100 mg/dL associated with a sleep duration of ³7, but <8 hours was significantly low as per analyses using all 3 models (model 1: 0.66 [0.49-0.89]; model 2: 0.69 [0.50-0.94]; model 3: 0.70 [0.51-0.95]). Significantly high OR values for HbA1c ³5.6% associated with a sleep duration of <5 hours were obtained in all 3 models (model 1: 1.52 [1.14-2.02]; model 2: 1.59 [1.16-2.19]; model 3: 1.52 [1.10-2.10]). While model 1 yielded a significantly high OR for HbA1c ³5.6% associated with a sleep duration of ³5, but <6 hours (1.20 [1.03-1.40]), no significant associations were yielded by the analyses using model 2 or 3.
3-4. Proportion of Participants with a Weight Gain of ³10 kg from the age of 20 years in Each Sleep Duration Category in the Men and Women
As shown in Figure 3, there was a significant U-curve relationship between the sleep duration and the proportion of men showing a weight gain of ³10 kg from the age of 20 years (p = 0.009), and the proportion of women showing a weight gain of ³10 kg from the age of 20 years increased significantly as the sleep duration decreased (p = 0.002). In addition, the proportion of men showing a weight gain of ³10 kg from the age of 20 years was significantly higher than the proportion of women showing a weight gain of ³10 kg from the age of 20 years across all sleep duration categories (p <0.0001).