Circadian Type Determines Working Ability: Poorer Working Ability in Evening-Types is Mediated by Insufficient Sleep in a Large Population-Based Sample of Working-Age Adults

Figures & data

Table 1 Descriptive Information on Sleep and Work Situation by Circadian Type in the Population-Based Study Sample of Finnish Working Age Adults

	Definite Evening-Type	Moderate Evening-Type	Moderate Morning-Type	Definite Morning-Type	p-value
Age (Mean in years, SD)	42.2 (11.7)	44.2 (11.6)	46.4 (11.3)	49.8 (10.2)	<0.001
Gender (%)					0.2
Men	46.2	46.6	45.1	44.2
Women	53.8	53.4	54.9	55.8
Season of responding by local photoperiod (%)					0.5
Winter	77.7	77.4	78.0	75.6
Spring	22.1	22.3	21.8	24.2
Summer	0.2	0.2	0.2	0.2
Daily mean sleep duration (Average in in hours and minutes, SD)	7h 28min (1h 23min)	7h 29min (1h 15min)	7h 29min (1h 13min)	7h 23min (1h 19min)	<0.05
Social jet lag (Average in hours and minutes, SD)	1h 28min (1h 20min)	1h 21min (1h 18min)	1h 11min (1h 8min)	54min (2h 16min)	<0.001
Insufficient sleep (%)					<0.001
Getting enough sleep nearly always	23.9	28.5	33.9	42.9
Getting enough sleep often	46.9	52.9	52.4	43.8
Getting enough sleep rarely/never	29.2	18.7	13.7	13.2
Insomnia symptoms (%)					<0.001
Often	14.6	8.5	7.4	9.5
Sometimes	42.7	44.5	45.7	42.3
Never	42.7	47.0	46.8	48.2
Diagnosed obstructive sleep apnea					0.2
No	97.0	97.4	98.1	97.1
Yes	3.0	2.6	1.9	2.9
General exhaustion (%)					<0.001
Never	18.2	19.7	21.1	25.9
Sometimes	57.2	63.8	64.4	59.2
Often	24.5	16.5	14.5	14.9
Physical work demand (%)					<0.001
Mainly sitting	56.9	49.8	46.1	45.9
Walking but no lifting	21.6	26.1	26.1	24.6
Walking and lifting	18.2	19.4	21.6	21.1
Heavy manual labor	3.2	4.7	6.2	7.4
Education level (%)					<0.001
Basic	10.4	10.9	14.9	21.1
Secondary	51.9	55.3	57.7	55.8
Higher	37.7	33.8	27.4	23.1
Employment (%)					<0.001
Permanent employment	59.3	62.6	62.9	62.8
Temporary employment	12.3	9.7	9.5	9.6
Independent entrepreneur	6.1	7.1	7.1	5.9
Full-time student	5.2	3.9	3.1	1.9
Maternity/paternity leave	2.0	2.6	2.2	1.3
Pensioned	6.1	5.7	7.2	9.7
On employment support	1.4	1.2	1.0	1.1
Unemployed	7.6	7.1	7.0	7.8
I can make many independent decisions in my job					<0.05
Completely agree	39.3	41.7	40.6	45.7
Somewhat agree	38.0	36.6	37.0	34.5
Neither agree nor disagree	9.1	9.8	10.4	8.8
Somewhat disagree	10.9	9.9	9.8	8.2
Completely disagree	2.7	2.1	2.3	2.8
I have a lot of say in how I can do my job (%)					<0.001
Completely agree	27.1	27.6	28.8	32.7
Somewhat agree	33.3	35.7	36.6	35.0
Neither agree nor disagree	19.8	17.4	17.7	16.4
Somewhat disagree	14.8	14.9	13.1	11.0
Completely disagree	5.0	4.3	3.9	4.9
I have very little freedom to decide how I do my job (%)					<0.01
Completely agree	5.2	3.8	3.4	4.8
Somewhat agree	11.0	11.9	10.7	12.3
Neither agree nor disagree	11.8	12.7	11.9	11.9
Somewhat disagree	39.2	38.8	40.2	34.3
Completely disagree	32.7	32.8	33.9	36.8
My job requires working very hard (%)					<0.001
Completely agree	27.5	26.1	25.6	32.2
Somewhat agree	34.9	37.5	36.6	35.0
Neither agree nor disagree	17.4	19.1	19.5	16.1
Somewhat disagree	14.5	13.3	14.0	12.6
Completely disagree	5.7	4.1	4.2	4.1
I am expected to do an unreasonable amount of work (%)					<0.001
Completely agree	8.0	5.4	4.9	8.0
Somewhat agree	15.1	14.3	15.1	17.3
Neither agree nor disagree	22.8	24.6	24.5	23.7
Somewhat disagree	30.3	31.9	31.6	27.7
Completely disagree	23.8	23.8	23.9	23.2
I do not have enough time to get my work done (%)					<0.01
Completely agree	8.0	6.6	5.9	7.5
Somewhat agree	23.7	20.9	19.1	20.3
Neither agree nor disagree	17.5	19.1	21.1	19.1
Somewhat disagree	29.5	30.3	30.4	27.9
Completely disagree	21.3	23.0	23.5	25.2

Abbreviations: SD, Standard deviation; p-value, Significance of the association between independent variable and dependent variable.

Figure 1 Distribution of circadian phenotypes by 10-years-wide age-groups among working-age adults.

Table 2 Work Well-Being as General Exhaustion and Working Ability by Circadian Type and Sleep as Insufficient Sleep and Social Jet Lag by Circadian Type. Generalized Linear Models, Adjusted with Age and Gender, with Definite Morning-Types are as the Reference Group. Percentages in the Table are Given Regarding General Exhaustion on Those Reporting General Exhaustion Often and Regarding Insufficient Sleep on Those Reporting Getting Rarely or Never Enough Sleep

	Definite Evening-Type					Moderate Evening-Type					Moderate Morning-Type					Definite Morning-Type
	%/Mean (SD)	B	95% CI		p-value	%/Mean (SD)	B	95% CI		p-value	%/Mean (SD)	B	95% CI		p-value	%/Mean (SD)
			Lower	Upper				Lower	Upper				Lower	Upper
Work well-being
General exhaustion
Ages 18 to 34	22.3	0.5	0.2	0.8	<0.001*	13.3	0.1	−0.2	0.4	0.5	14.0	0.1	−0.2	0.4	0.4	15.9
Ages 35 to 44	23.6	0.4	0.2	0.7	<0.001*	18.0	0.2	−0.004	0.4	0.05	15.2	0.04	−0.2	0.3	0.7	17.4
Ages 45 to 54	31.8	0.8	0.6	0.4	<0.001*	17.7	0.3	0.06	0.4	<0.05	15.2	0.1	−0.05	0.3	0.1	15.4
Ages 55 to 64	21.9	0.6	0.3	0.8	<0.001*	17.2	0.4	0.2	0.6	<0.001*	13.5	0.2	0.02	0.4	<0.05	13.1
Working ability
Ages 18 to 34	9.0 (1.4)	0.03	−0.2	0.2	0.8	9.1 (1.3)	0.2	−0.04	0.4	0.1	9.2 (1.3)	0.2	−0.009	0.4	0.06	9.0 (1.6)
Ages 35 to 44	8.5 (1.9)	−0.4	−0.6	−0.2	<0.001*	8.7 (1.6)	−0.2	−0.3	0.03	0.1	8.8 (1.6)	−0.09	−0.3	0.1	0.3	8.9 (1.4)
Ages 45 to 54	7.8 (2.4)	−0.5	−0.7	−0.3	<0.001*	8.3 (1.8)	−0.01	−0.2	0.2	0.9	8.3 (1.9)	0.06	−0.1	0.02	0.5	8.3 (1.9)
Ages 55 to 64	7.1 (2.6)	0.01	−0.3	0.3	0.9	7.2 (2.4)	0.06	0.2	0.3	0.6	7.3 (2.4)	0.2	−0.001	0.4	0.05	7.1 (2.5)
Sleep
Insufficient sleep
Ages 18 to 34	28.4	1.1	0.8	1.4	<0.001*	19.4	0.8	0.6	1.1	<0.001*	16.8	0.6	0.3	0.9	<0.001*	12.2
Ages 35 to 44	33.4	1.1	0.8	1.3	<0.001*	22.3	0.6	0.4	0.8	<0.001*	14.9	0.3	0.08	0.5	<0.01	15.9
Ages 45 to 54	29.0	0.9	0.7	1.2	<0.001*	18.2	0.5	0.3	0.6	<0.001*	13.6	0.2	−0.007	0.4	0.06	14.0
Ages 55 to 64	24.9	0.7	0.5	0.9	<0.001*	14.5	0.3	0.1	0.5	<0.001*	11.0	0.2	0.01	0.3	<0.05	11.6
Social jet lag in hours and minutes
Ages 18 to 34	1h 49min (1h 28min)	1.1	0.8	1.4	<0.001*	1h 30min (1h 45min)	0.8	0.6	1.1	<0.001*	1h 28min (48min)	0.6	0.3	0.8	<0.001*	1h 1min (2h 38min)
Ages 35 to 44	1h 26min (1h 14min)	1.1	0.8	1.3	<0.001*	1h 23min (1h 13min)	0.6	0.4	0.8	<0.001*	1h 4min (2h 12min)	0.3	0.08	0.5	<0.01	49min (2h 56min)
Ages 45 to 54	1h 26min (1h 17min)	0.9	0.7	1.2	<0.001*	1h 28min (50min)	0.5	0.3	0.6	<0.001*	1h 12min (1h 11min)	0.2	−0.007	0.4	0.06	1h 8min (2h 10min)
Ages 55 to 64	1h 2min (1h 13min)	0.7	0.5	0.9	<0.001*	1h 5 min (1h 11min)	0.3	0.1	0.5	<0.001*	1h 5min (1h 15min)	0.2	0.01	0.3	<0.05	43min (1h 47min)

Note: *Bonferroni corrected p-value <0.05.

Abbreviations: SD, Standard deviation; B, estimated coefficient; 95% CI, 95% confidence intervals; p-value, Significance of the association between independent variable and dependent variable.

Table 3 Working Ability by Insufficient Sleep and Social Jet Lag for Each Circadian Type Separately. Generalized Linear Models, Adjusted with Age and Gender, with Those Getting Enough Sleep as the Reference Group

	Definite Evening-Type					Moderate Evening-Type					Moderate Morning-Type					Definite Morning-Type
	Mean (SD)	B	95% CI		p-value	Mean (SD)	B	95% CI		p-value	Mean (SD)	B	95% CI		p-value	Mean (SD)	B	95% CI		p-value
			Lower	Upper				Lower	Upper				Lower	Upper				Lower	Upper
Working ability among those getting enough sleep rarely/never
Ages 18 to 34	8.8 (1.6)	−0.4	−0.8	−0.1	<0.01	8.8 (1.5)	−0.5	−0.8	−0.3	<0.001*	9.0 (1.3)	−0.2	−0.5	0.1	0.2	8.9 (1.2)	−0.3	−1.1	0.9	0.3
Ages 35 to 44	8.2 (2.0)	−0.6	−1.0	−0.09	<0.05	8.5 (1.5)	−0.2	−0.5	0.09	0.2	8.4 (1.7)	−0.6	−0.9	−0.3	<0.001*	8.3 (1.9)	−0.7	−1.1	−0.3	<0.001*
Ages 45 to 54	7.6 (2.1)	−0.05	−0.7	0.6	0.9	7.9 (1.9)	−0.5	−0.9	−0.2	<0.01	7.9 (1.9)	−0.5	−0.9	−0.2	<0.01	7.3 (2.7)	−1.4	−1.8	−1.0	<0.001*
Ages 55 to 64	6.7 (2.7)	−0.2	−0.9	0.5	0.6	7.0 (2.5)	−0.4	−0.8	0.1	0.2	6.5 (2.7)	−1.1	−1.5	−0.6	<0.001*	6.2 (3.0)	−1.1	−1.7	−0.6	<0.001*
Working ability among those getting enough sleep often
Ages 18 to 34	9.0 (1.2)	−0.2	−0.5	0.07	0.1	9.2 (1.2)	−0.2	−0.4	0.05	0.1	9.2 (1.2)	0.06	−0.2	0.3	0.6	8.8 (2.0)	−0.4	−0.9	0.07	0.09
Ages 35 to 44	8.8 (1.6)	0.005	−0.4	0.5	0.9	8.9 (1.3)	0.2	−0.08	0.4	0.2	8.9 (1.4)	−0.2	−0.4	0.04	0.1	9.0 (1.1)	0.03	−0.3	0.3	0.8
Ages 45 to 54	8.2 (2.1)	0.5	−0.06	1.1	0.08	8.4 (1.7)	−0.06	−0.3	0.2	0.7	8.5 (1.6)	0.02	−0.2	0.3	0.9	8.4 (1.7)	−0.3	−0.6	0.001	0.05
Ages 55 to 64	7.6 (2.3)	0.8	0.1	1.4	<0.05	7.3 (2.3)	−0.02	−0.4	0.3	0.9	7.4 (2.2)	−0.2	−0.4	0.1	0.3	7.2 (2.3)	−0.03	−0.4	0.3	0.9
Working ability among those getting enough sleep nearly always
Ages 18 to 34	9.3 (1.2)	ref.				9.3 (1.2)	ref.				9.2 (1.4)	ref.				9.2 (1.2)	ref.
Ages 35 to 44	8.8 (1.7)	ref.				8.7 (2.0)	ref.				9.0 (1.5)	ref.				9.0 (1.3)	ref.
Ages 45 to 54	7.6 (2.7)	ref.				8.4 (1.9)	ref.				8.4 (2.0)	ref.				8.7 (1.5)	ref.
Ages 55 to 64	6.9 (2.8)	ref.				7.3 (2.4)	ref.				7.6 (2.4)	ref.				7.3 (2.4)	ref.
Working ability by Social jet lag
Ages 18 to 34	Table 2	3.6×10^−6	−3.1×10^−5	3.8×10^−5	0.8	Table 2	8.9×10^−6	−1.2×10^−5	3.0×10^−5	0.4	Table 2	5.4×10^−5	6.5×10^−6	0.0001	<0.05	Table 2	−6.8×10^−6	−2.6×10^−5	1.2×10^−5	0.5
Ages 35 to 44	Table 2	1.5×10^−5	−2.6×10^−5	5.6×10^−5	0.5	Table 2	3.8×10^−6	−2.4×10^−5	3.2×10^−5	0.8	Table 2	1.4×10^−5	−9.2×10^−6	3.7×10^−5	0.2	Table 2	−9.1×10^−8	−2.1×10^−5	2.1×10^−5	0.9
Ages 45 to 54	Table 2	1.9×10^−5	−3.5×10^−5	7.3×10^−5	0.5	Table 2	7.2×10^−5	2.4×10^−5	0.0001	<0.01	Table 2	2.9×10^−5	−2.4×10^−7	5.8×10^−5	0.05	Table 2	−2.8×10^−6	−2.6×10^−5	−2.1×10^−5	0.8
Ages 55 to 64	Table 2	0.0001	4.1×10^−5	0.0002	<0.01	Table 2	8.9×10^−5	4.5×10^−5	0.0001	<0.001*	Table 2	5.6×10^−5	1.8×10^−5	9.3×10^−5	<0.01	Table 2	6.9×10^−5	2.7×10^−5	0.0001	0.001*

Note: *Bonferroni corrected p-value <0.05.

Abbreviations: SD, Standard deviation; B, estimated coefficient; 95% CI, 95% confidence intervals; p-value, Significance of the association between independent variable and dependent variable; ref, reference group.

Figure 2 Mediation analysis with insufficient sleep as a mediator for the association between circadian type and working ability. Direct effect is the association between circadian type and working ability while controlling for insufficient sleep. Indirect effect is the measure of the mediation effect. (A) Mediation analyses for those aged 35 to 44 years, and (B) for those aged 45 to 55 years.