Correlation among stress, salivary alpha amylase, HRV, and sleep behaviors (N = 86)_
| Variables | Sleep behaviors, r (P) | |
|---|---|---|
| Time in bed | SE | |
| Age | 0.225 (0.041) | −0.004 (0.972) |
| Female sex | −0.099 (0.372) | 0.322 (0.003) |
| BMI | 0.121 (0.277) | −0.260 (0.018) |
| Monthly expenditure | 0.138 (0.215) | 0.192 (0.082) |
| Regular smoking | −0.144 (0.192) | −0.066 (0.555) |
| Drinking alcohol | 0.124 (0.269) | −0.083 (0.463) |
| Stress | −0.276 (0.011) | 0.034 (0.760) |
| Salivary alpha amylase | 0.266 (0.030) | 0.097 (0.435) |
| HRV indices at resting | ||
| Mean HR (beat/min) | −0.116 (0.301) | −0.131 (0.240) |
| Mean RR interval (millisecond) | 0.090 (0.420) | 0.118 (0.293) |
| SDNN (millisecond) | 0.061 (0.589) | 0.119 (0.288) |
| LnRMSSD (millisecond) | 0.018 (0.870) | 0.191 (0.086) |
| nLF (%) | −0.076 (0.500) | −0.316 (0.004) |
| nHF (%) | 0.076 (0.500) | 0.316 (0.004) |
| LF/HF (a.u) | −0.129 (0.249) | −0.227 (0.040) |
General characteristics and study variables in the participants (N = 86)_
| Variables | Mean ± SD or n (%) |
|---|---|
| Age (years) | 22.0 ± 1.94 |
| Sex | |
| Male | 47 (54.7) |
| Female | 39 (45.3) |
| BMI | 22.3 ± 2.42 |
| Monthly expenditure | |
| <300 K won | 42 (48.8) |
| 300 K–490 K won | 28 (32.6) |
| >500 K won | 16 (18.6) |
| Regular smoking | |
| No | 78 (90.7) |
| Yes | 8 (9.3) |
| Drinking alcohol | |
| Everyday | 6 (7.0) |
| Occasionally | 78 (90.7) |
| None | 2 (2.3) |
| Time in bed (minutes) | 408.5 ± 81.99 |
| Sleep minutes (minutes) | 325.9 ± 77.36 |
| WASO (minutes) | 62.7 ± 30.82 |
| WE (times) | 23.1 ± 9.05 |
| MWE (minutes) | 4.5 ± 4.38 |
| SE (%) | 84.0 ± 7.22 |
| Stress | 26.1 ± 10.76 |
| Salivary alpha amylase (U/ml) | 65.8 ± 45.11 |
| HRV indices at resting | |
| Mean HR (beat per minute) | 71.3 ± 11.31 |
| Mean RR interval (millisecond) | 862.5 ± 135.35 |
| SDNN (millisecond) | 51.1 ± 22.0 |
| RMSSD (millisecond) | 45.9 ± 31.3 |
| nLF (%) | 54.6 ± 18.76 |
| nHF (%) | 45.4 ± 18.76 |
| LF/HF (a.u) | 1.8 ± 1.56 |
Factors influencing time in bed and sleep efficiency_
| Variables | B | SE | β | T | P | R2 | F |
|---|---|---|---|---|---|---|---|
| Time in bed | 0.040 | 0.147 | 2.670 | ||||
| Constant | 199.751 | 114.318 | 1.747 | 0.086 | |||
| Age | 9.774 | 4.962 | 0.241 | 1.970 | 0.053 | ||
| Female sex | −1.588 | 19.762 | −0.010 | −0.080 | 0.936 | ||
| Stress | −1.066 | 0.929 | −0.138 | −1.147 | 0.256 | ||
| Salivary alpha amylase | 0.426 | 0.208 | 0.244 | 2.052 | 0.044 | ||
| SE | 0.001 | 0.207 | 5.035 | ||||
| Constant | 83.475 | 10.911 | 7.651 | 0.000 | |||
| Age | 0.453 | 0.396 | 0.123 | 1.141 | 0.257 | ||
| Female sex | 3.050 | 1.706 | 0.211 | 1.788 | 0.078 | ||
| BMI | −0.677 | 0.329 | −0.224 | −2.057 | 0.043 | ||
| nHF | 0.094 | 0.041 | 0.245 | 2.262 | 0.027 |
Stress and its association with salivary alpha amylase and HRV (N = 86)_
| Items | Stress | |||
|---|---|---|---|---|
| r (p) | Adjusted for age and sex | |||
| β | SE | p | ||
| nHF on HRV | −0.164 (0.137) | −0.224 | 0.179 | 0.034 |
| Salivary alpha amylase | −0.129 (0.288) | −0.113 | 0.554 | 0.366 |