Shift work aggravates metabolic syndrome development among early-middle-aged males with elevated ALT

Table 1 Job contents for different job types/e-ALT of the workers in this investigation n (%)

Job title	Routine work activities	n = 996	e-ALT: no; pRSW: no (n = 496)	e-ALT: no; pRSW: yes (n = 310)	e-ALT: yes; pRSW: no (n = 119)	e-ALT: yes; pRSW: yes (n = 71)
Operator	On-site work	232 (23.3)	101	97	17	17
Technician	On-site work	422 (42.4)	158	178	40	46
Engineer	On-site work	159 (16.0)	131	2	24	2
Team leader	On-site work	85 (8.5)	33	29	18	5
Specialist	On-site work	22 (2.2)	16	1	5	0
Deputy manager	Management	42 (4.2)	31	1	10	0
General manager	Management	19 (1.9)	15	0	4	0
Director	Management	3 (0.3)	3	0	0	0
Guard	Security	8 (0.8)	6	1	1	0
Clerk	Office work	4 (0.4)	2	1	0	1

e-ALT: Elevated alanine aminotransferase; pRSW: Persistent rotating shift work.

Table 2 Baseline characteristics of subjects stratified by e-ALT¹ and pRSW status n (%)

Measurement (SD)	Total population (n = 996)	e-ALT: no; pRSW: no (n = 496)	e-ALT: no; pRSW: yes (n = 310)	e-ALT: yes; pRSW: no (n = 119)	e-ALT: yes; pRSW: yes (n = 71)	P value2
Age (yr)	32.1 (5.9)	32.8 (6.0)	30.9 (5.8)	32.6 (5.3)	31.4 (5.7)	0.0001
Body mass index (kg/m2)	23.4 (2.9)	23.2 (2.8)	22.7 (2.8)	25.0 (2.5)	25.0 (3.0)	< 0.0001
Waist (cm)	78.3 (7.6)	78.1 (7.4)	76.4 (7.4)	82.5 (6.3)	81.3 (8.1)	< 0.0001
Systolic blood pressure (mmHg)	119.2 (14.1)	118.2 (13.8)	118.2 (14.3)	123.0 (14.0)	123.5 (14.1)	0.0002
Diastolic blood pressure (mmHg)	72.9 (9.0)	72.3 (8.6)	72.3 (8.9)	75.4 (10.0)	75.7 (9.3)	0.0002
Fasting blood glucose (mg/dL)	94.5 (14.8)	95.2 (18.6)	92.9 (8.1)	95.1 (8.1)	94.5 (15.2)	0.1797
Triglycerides (mg/dL)	113.1 (86.3)	109.3 (97.8)	101.0 (55.6)	149.3 (96.0)	132.2 (74.7)	< 0.0001
HDL cholesterol (mg/dL)	48.6 (11.0)	49.3 (10.9)	49.6 (11.4)	45.2 (10.8)	44.9 (7.9)	< 0.0001
Alanine aminotransferase (U/L)	31.0 (29.4)	21.7 (7.7)	21.1 (8.4)	68.8 (42.6)	75.8 (54.3)	< 0.0001
Aspartate aminotransferase (U/L)	25.8 (17.9)	21.9 (5.1)	21.8 (5.5)	39.3 (23.3)	48.5 (47.8)	< 0.0001
Insulin (mg/dL)	8.5 (6.2)	8.0 (4.9)	7.4 (5.2)	11.4 (7.8)	11.6 (11.4)	< 0.0001

¹ALT > 40 mg/dL;

²ANOVA was conducted, using Tukey’s test.

Table 3 Baseline abnormality rates of subjects stratified by e-ALT¹ and pRSW status

Abnormalities	Total population (n = 996)	e-ALT: no; pRSW: no (n = 496)	e-ALT: no; pRSW: yes (n = 310)	e-ALT: yes; pRSW: no (n = 119)	e-ALT: yes; pRSW: yes (n = 71)	P value2
MetS-component abnormality (%)
Central obesity	3.6 (36/996)	2.8	3.2	5.9	7.0	0.1595
Hyperglycemia	20.7 (206/996)	22.0	18.4	22.7	18.3	0.5658
Hypertriglyceridemia	17.5 (174/996)	15.1	13.2	34.5	23.9	< 0.0001
Elevated blood pressure	21.3 (212/996)	18.3	20.6	29.4	31.0	0.01
Hypo-HDL cholesterol	20.2 (201/996)	18.5	17.1	32.8	23.9	0.0018
Elevated alanine aminotransferase	19.1 (190/996)
Hepatovirus B carrier	19.3 (192/996)	18.1	14.8	27.7	32.4	0.0005
Hepatovirus C carrier	1.2 (12/996)	0.4	0.3	4.2	5.6	< 0.0001
Fatty Liver	30.8 (307/996)	24.0	21.0	66.4	62.0	< 0.0001
Lifestyle factor (%)
Ever been a smoker (≥ 1 yr)	42.7 (425/996)	36.9	51.6	39.5	49.3	0.0003
Having snacks before sleeping (≥ 1 d/wk)	42.5 (423/996)	37.7	51.9	39.5	39.4	0.0008
Having snacks between meals (≥ 1 d/wk)	40.9 (407/996)	40.5	39.4	47.1	39.4	0.5192
Physical exercise (≥ 3 times/wk)	34.6 (345/996)	38.5	31.6	31.9	25.4	0.0545
Habitual drinker (≥ 1 d/wk)	10 (99/996)	8.7	10.6	10.1	15.5	0.3196
Workplace factor (%)
Persistent day-night rotating shift work	38.3 (381/996)
On-site worker	92.4 (920/996)	88.5	99.1	87.4	98.6	< 0.0001
Development of MetS within 5 yr	14.2 (141/996)	11.1	8.7	27.7	36.6	< 0.0001

¹ALT > 40 mg/dL;

²χ² test was conducted for abnormalities and four liver function/shift work subgroups. MetS: Metabolic syndrome.

Table 4 Change of abnormalities based on a 5-year follow-up among the subgroups stratified by ALT and shift work (%)

MetS and its components	e-ALT initially	pRSW exposure	Baseline	P value1	5th yr	P value1	Δ 5th yr vs baseline
Central obesity	No	No	2.8	0.1595	22.2	0.0037	19.4
		Yes	3.2		20.0		16.8
	Yes	No	5.9		33.6		27.7
		Yes	7.0		33.8		26.8
Hyperglycemia	No	No	22.0	0.5658	16.7	< 0.0001	-5.2
		Yes	18.4		13.9		-4.5
	Yes	No	22.7		26.9		4.2
		Yes	18.3		33.8		15.5
Hypertriglyceridemia	No	No	15.1	< 0.0001	26.8	< 0.0001	11.7
		Yes	13.2		25.5		12.3
	Yes	No	34.5		42.0		7.6
		Yes	23.9		45.1		21.1
Elevated blood pressure	No	No	18.3	0.01	48.0	0.1025	29.6
		Yes	20.6		50.0		29.4
	Yes	No	29.4		55.5		26.1
		Yes	31.0		62.0		31.0
Hypo-HDL cholesterol	No	No	18.5	0.0018	6.3	< 0.0001	-12.3
		Yes	17.1		8.1		-9.0
	Yes	No	32.8		17.6		-15.1
		Yes	23.9		23.9		0.0
Development of MetS within 5 yr	No	No			11.1	< 0.0001
		Yes			8.7
	Yes	No			27.7
		Yes			36.6
MetS-component numbers (mode)	No	No	0		1		0
		Yes	0		1		0
	Yes	No	2		1		0
		Yes	1		2		1

¹χ² test was conducted, four abnormalities of subgroups were constructed. Δ: Differences between 2007 and 2002; plus indicates increasing and minus indicates decreasing trend within follow-up.

Table 5 Multivariate analysis for the risk of development of metabolic syndrome among male workers

Adjustment for initial characteristics			OR1 (e-ALT: no vs pRSW: no)	95% CI
Model 1	Age (yr)	e-ALT: no; pRSW: yes	0.8	0.5-1.3
		e-ALT: yes; pRSW: no	3.1	1.9-5.0
		e-ALT: yes; pRSW: yes	4.7	2.7-8.2
Model 2	Age, MetS-components, insulin resistance	e-ALT: no; pRSW: yes	0.8	0.5-1.3
		e-ALT: yes; pRSW: no	1.8	1.03-3.0
		e-ALT: yes; pRSW: yes	3.8	2.0-6.9
Model 3	Age, MetS-components, insulin resistance, hepatovirus infections	e-ALT: no; pRSW: yes	0.8	0.5-1.3
		e-ALT: yes; pRSW: no	1.9	1.1-3.2
		e-ALT: yes; pRSW: yes	4.0	2.1-7.4
Model 4	Age, MetS-components, insulin resistance, hepatovirus infections, fatty liver	e-ALT: no; pRSW: yes	0.8	0.5-1.3
		e-ALT: yes; pRSW: no	1.4	0.8-2.4
		e-ALT: yes; pRSW: yes	2.9	1.5-5.5
Model 5	Age, MetS-components, insulin resistance, hepatovirus infections, fatty liver, lifestyle and workplace factors	e-ALT: no; pRSW: yes	0.7	0.4-1.2
		e-ALT: yes; pRSW: no	1.3	0.7-2.3
		e-ALT: yes; pRSW: yes	2.7	1.4-5.3

¹Each variant put into the model as categorical data. OR: Odds ratio; CI: Confidence interval.