Morning preference is associated with subjective happiness among Japanese female workers: A moderation analysis by sleep characteristics from the SLEPT study

Figures & data

Table 1. Characteristics of the subjects by gender

	Male	Female
	n = 205	n = 272
Catetgorical variables	n (%)	n (%)
Diurnal preference (MEQ score)
Evening type (16–52)	68 (33.2)	94 (34.6)
Intermediate type (53–64)	95 (46.3)	136 (50.0)
Morning type (65–86)	42 (20.5)	42 (15.4)
Physical activity
Yes	50 (24.4)	38 (14.0)
No	155 (75.6)	234 (86.0)
Drinking habit
Less than once a week	86 (42.0)	175 (64.3)
Once a week or more	119 (58.0)	97 (35.7)
Smoking habit
Non-smoker	180 (87.8)	254 (93.4)
Current smoker	25 (12.2)	18 (6.6)
BMI
≤18.4	7 (3.4)	31 (11.4)
18.5–24.9	150 (73.2)	200 (73.5)
≥25.0	48 (23.4)	41 (15.1)
Medical history of chronic disease
No	141 (68.8)	221 (81.3)
Yes	63 (30.7)	44 (16.2)
Non-specified	1 (0.5)	7 (2.6)
Occupation
Clerical work	53 (25.9)	169 (62.1)
Professional/technical	114 (55.6)	77 (28.3)
Manager	28 (13.7)	7 (2.6)
Sales job	2 (1.0)	2 (0.7)
Service job	6 (2.9)	17 (6.3)
Employment status
Full-time regular employees	176 (85.9)	122 (44.9)
Short-time regular employees	0 (0.0)	6 (2.2)
Fixed-term employees	21 (10.2)	78 (28.7)
Part-time employees	1 (0.5)	60 (22.1)
Managers, executives	3 (1.5)	2 (0.7)
Others	4 (2.0)	4 (1.5)
Continuous variables	median (IQR)	median (IQR)
Age	43 (33–52)	42 (33–49)
Self-rated health	2 (1–2)	2 (1–3)
K6	3 (1–6)	4 (1–7)
Quantitative workload	2.3 (1.8–3.0)	2.0 (1.3–2.3)
Qualitative workload	2.3 (2.0–3.0)	2.0 (1.3–2.3)
Interpersonal difficulties	2.0 (1.3–2.3)	1.7 (1.3–2.3)
Reward from work	3.0 (2.7–4.0)	2.7 (2.0–3.3)
Job control	3.0 (2.7–3.7)	3.0 (2.3–3.3)
Social support	3.0 (2.5–3.3)	3.0 (2.8–3.5)
One-way commute time, min	25 (15–40)	30 (15–45)
Working hours in a recent week, h	50 (45–60)	42 (36–50)

Abbreviations: IQR = interquartile range, BMI = body mass index, K6 = Kessler Psychological Distress Scale.

Table 2. Median, IQRs, and correlations among subjective happiness, MEQ score, and sleep-related factors (male)

		bivariate correlation
	median (IQR)	1	2	a	b	c	d	e	f	g
1. Subjective happiness	3 (3–3)
2. MEQ score	57 (49–64)	0.109
a. Subjective sleep quality	1 (1–2)	−0.286**	−0.201**
b. Sleep disturbance	1 (0–1)	−0.109	0.168*	0.212**
c. ESS score	10 (7–12)	−0.122	−0.128	0.281**	0.085
d. Weekend oversleep	0 (0–1)	−0.031	−0.372**	0.072	−0.105	0.050
e. Total sleep time, min	319.1 (280.7–350.9)	0.027	−0.034	−0.076	0.030	−0.102	0.008
f. Sleep onset time, h	00:23 (23:38–01:14)	−0.010	−0.560**	0.179*	−0.027	0.161*	0.334**	−0.343**
g. Wake time, h	06:41 (06:01–07:25)	0.015	−0.669**	0.149*	−0.007	0.061	0.353**	0.143*	0.754**
h. Sleep efficiency, %	80.2 (72.5–85.9)	−0.022	−0.042	0.048	−0.005	−0.004	0.031	0.616**	0.029	0.035

Spearman’s rank correlation coefficient.

* p < .05, ** p < .01.

Abbreviations: IQR = interquartile range, MEQ = Morningness-Eveningness Questionnaire, ESS = Epworth Sleepiness Scale.

Table 3. Median, IQRs, and correlations among subjective happiness, MEQ score, and sleep-related factors (female)

		bivariate correlation
	median (IQR)	1	2	a	b	c	d	e	f	g
1. Subjective happiness	3 (2–3)
2. MEQ score	56 (50–62)	0.243**
a. Subjective sleep quality	1 (1–2)	−0.123*	−0.132*
b. Sleep disturbance	1 (1–1)	−0.105	0.035	0.278**
c. ESS score	10 (8–13)	−0.167**	−0.140*	0.140*	−0.027
d. Weekend oversleep	0 (0–1)	−0.158**	−0.476**	0.144*	−0.055	0.046
e. Total sleep time, min	338.7 (304.1–376.8)	0.107	0.018	−0.103	0.097	−0.112	0.011
f. Sleep onset time, h	00:07 (23:34–01:05)	−0.121*	−0.558**	0.142*	−0.061	0.032	0.377**	−0.339**
g. Wake time, h	06:39 (05:59–07:15)	−0.092	−0.606**	0.019	0.016	−0.064	0.358**	0.285**	0.623**
h. Sleep efficiency, %	85.1 (79.3–90.3)	0.117	0.019	−0.034	0.000	0.009	0.091	0.477**	0.051	−0.005

Spearman’s rank correlation coefficient.

* p < .05, ** p < .01.

Abbreviations: IQR = interquartile range, MEQ = Morningness-Eveningness Questionnaire, ESS = Epworth Sleepiness Scale.

Table 4. Results of a series of moderation analysis, subjective happiness as dependent variable (male)

		B	SE	β	t	P-value
Step 1, R^2 = 0.247	Age	0.002	0.004	0.03	0.491	.624
	Self-rated health	−0.241	0.054	−0.309	−4.421	<.001
	K6 score	−0.05	0.013	−0.265	−3.783	<.001
Step 2, R^2 = 0.307	Reward from work	0.226	0.081	0.188	2.793	.006
	Social support	0.143	0.062	0.156	2.304	.022
Step 3, R^2 = 0.311	MEQ score	0.005	0.005	0.071	1.131	.260
Step 4a, R^2 = 0.314	Subjective sleep quality	−0.075	0.082	−0.062	−0.911	.364
Step 5a, R^2 = 0.315	Subjective sleep quality × MEQ score	−0.003	0.007	−0.029	−0.482	.630
Step 4b, R^2 = 0.311	Sleep disturbance	−0.014	0.101	−0.009	−0.139	.889
Step 5b, R^2 = 0.312	Sleep disturbance × MEQ score	−0.005	0.010	−0.029	−0.475	.635
Step 4c, R^2 = 0.312	ESS score	0.005	0.011	0.028	0.433	.665
Step 5c, R^2 = 0.315	ESS score × MEQ score	0.001	0.001	0.060	1.002	.318
Step 4d, R^2 = 0.312	Weekend oversleep	−0.046	0.100	−0.030	−0.463	.644
Step 5d, R^2 = 0.318	Weekend oversleep × MEQ score	0.014	0.010	0.088	1.345	.180
Step 4e, R^2 = 0.311	Total sleep time	0.000	0.001	0.005	0.081	.935
Step 5e, R^2 = 0.312	Total sleep time × MEQ score	0.000	<0.001	0.015	0.241	.809
Step 4f, R^2 = 0.314	Sleep onset time	0.000	<0.001	0.059	0.788	.431
Step 5f, R^2 = 0.314	Sleep onset time × MEQ score	0.000	<0.001	−0.023	−0.374	.709
Step 4g, R^2 = 0.320	Wake time	0.000	<0.001	0.134	1.586	.114
Step 5g, R^2 = 0.321	Wake time × MEQ score	0.000	<0.001	0.029	0.489	.626
Step 4h, R^2 = 0.311	Sleep efficiency	−0.001	0.004	−0.011	−0.184	.854
Step 5h, R^2 = 0.314	Sleep efficiency × MEQ score	0.000	<0.001	−0.055	−0.916	.361

Hierarchical multiple regression analysis.

Abbreviations: K6 = Kessler Psychological Distress Scale, MEQ = Morningness-Eveningness Questionnaire, ESS = Epworth Sleepiness Scale.

Table 5. Results of a series of moderation analysis, subjective happiness as dependent variable (female)

		B	SE	β	t	P-value
Step 1, R^2 = 0.134	Age	−0.002	0.005	−0.025	−0.426	.670
	Self-rated health	−0.107	0.053	−0.126	−2.025	.044
	K6 score	−0.059	0.012	−0.301	−4.812	<.001
Step 2, R^2 = 0.164	Reward from work	0.159	0.052	0.174	3.044	.003
Step 3, R^2 = 0.193	MEQ score	0.016	0.005	0.181	3.123	.002
Step 4a, R^2 = 0.193	Subjective sleep quality	0.005	0.078	0.004	0.060	.952
Step 5a, R^2 = 0.193	Subjective sleep quality × MEQ score	−0.001	0.008	−0.009	−0.168	.867
Step 4b, R^2 = 0.196	Sleep disturbance	−0.085	0.093	−0.052	−0.911	.363
Step 5b, R^2 = 0.196	Sleep disturbance × MEQ score	−0.003	0.011	−0.018	−0.311	.756
Step 4c, R^2 = 0.194	ESS score	−0.006	0.011	−0.034	−0.583	.560
Step 5c, R^2 = 0.194	ESS score × MEQ score	0.000	0.001	−0.002	−0.028	.978
Step 4d, R^2 = 0.195	Weekend oversleep	−0.079	0.098	−0.051	−0.804	.422
Step 5d, R^2 = 0.197	Weekend oversleep × MEQ score	−0.008	0.011	−0.040	−0.719	.473
Step 4e, R^2 = 0.201	Total sleep time	0.001	0.001	0.092	1.641	.102
Step 5e, R^2 = 0.202	Total sleep time × MEQ score	0.000	<0.001	−0.029	−0.529	.597
Step 4f, R^2 = 0.194	Sleep onset time	0.000	<0.001	−0.034	−0.506	.613
Step 5f, R^2 = 0.194	Sleep onset time × MEQ score	0.000	<0.001	−0.010	−0.185	.854
Step 4g, R^2 = 0.194	Wake time	0.000	<0.001	−0.029	−0.415	.678
Step 5g, R^2 = 0.194	Wake time × MEQ score	0.000	<0.001	−0.021	−0.373	.709
Step 4h, R^2 = 0.207	Sleep efficiency	0.011	0.005	0.120	2.163	.031
Step 5h, R^2 = 0.210	Sleep efficiency × MEQ score	0.001	0.001	0.051	0.928	.354

Hierarchical multiple regression analysis.

Abbreviations: K6 = Kessler Psychological Distress Scale, MEQ = Morningness-Eveningness Questionnaire, ESS = Epworth Sleepiness Scale.