The relationship between serum vitamin D levels and sleep quality in fixed day indoor field workers in the electronics manufacturing industry in Korea

Table 1 Subject characteristics

Variables		Number (%)		Vitamin D (ng/mL)	P value^a
Variables		Number (%)		Mean (SD)^b	P value^a
Total		1472	(100)	13.70 5.93
Age, years	≥30	813	(55.2)	14.56 6.14	0.009
Age, years	<30	659	(44.8)	13.25 5.63
Sex	Male	1178	(80.0)	14.29 6.00	<0.001
Sex	Female	294	(20.0)	11.31 4.95
Regular exercise, times per week	≥3	535	(36.3)	14.37 6.09	0.001
Regular exercise, times per week	<3	937	(63.7)	13.31 5.80
Smoking	Current	428	(29.1)	14.83 6.42	<0.001
Smoking	Never/former	1044	(70.9)	13.23 5.65
Risky drinking^b	Yes	384	(26.1)	14.51 5.77	0.002
Risky drinking^b	No	1088	(73.9)	13.41 6.28
Body mass index, kg/m²	<25	948	(64.4)	13.69 6.03	0.995
Body mass index, kg/m²	≥25	524	(35.6)	13.70 5.74
Marital status	Married	774	(52.6)	14.31 6.13	<0.001
Marital status	Unmarried	698	(47.4)	13.01 5.62
Education level	≥College	994	(67.5)	13.83 5.94	0.20
Education level	≤Highs chool	478	(32.5)	13.41 5.89
Job tenure, years	<5	468	(31.8)	12.98 5.59	0.001
	5–9	383	(26.0)	14.51 6.35
	≥10	621	(42.2)	13.73 5.84
Job stress	Low	1152	(78.2)	13.72 5.95	0.766
Job stress	High	321	(21.8)	13.61 5.86
Test season^c	Spring	300	(20.4)	12.53 5.09	0.001
	Summer	456	(31.0)	16.87 6.11
	Autumn	150	(10.2)	14.52 5.86
	Winter	566	(38.5)	11.54 5.93

^aComparison made using the Student t-test
^bRisky drinking: 2 or more times per week and 7 (females: 5) or more drinks per drinking session
^cSpring, March–May; summer, June–August; autumn, September–November; winter, December–February

ISSN: 2052-4374