Outdoor light at night and depressive symptoms in male veterans: a multicenter cross-sectional study in China

Figures & data

Figure 1. Locations of veteran communities.

Abbreviations: LAN, light at night.

Table 1. Demographic characteristics of depressive symptoms cases and controls.

Variables	Overall		Depressive symptoms cases		Controls		p-value
	N	%	N	%	N	%
Age (mean ± SD)^a	82.1	4.0	83.0	3.3	82.1	4.0	<.001
Years of education^b							.01
≤9	4195	65.1	312	70.9	3883	64.7
>9	2250	34.9	128	29.1	2122	35.3
Regular physical activities^c							<.001
Yes	5525	85.7	287	65.2	5235	87.2
No	920	14.3	153	34.8	767	12.8
Regular social activities^d							<.001
Yes	2427	37.7	131	39.8	2296	38.2
No	4018	62.3	309	70.2	3709	61.8
Smoking							.03
Current smoker	538	8.3	32	7.3	506	8.4
Ex-smoker	2271	35.2	180	40.9	2091	34.8
Non-smoker	3636	56.4	228	51.8	3408	56.8
Drinking							.001
>2 times/week	497	7.7	24	5.5	473	7.9
≤2 times/week	1592	24.7	100	22.7	1492	24.8
Quit	1051	16.3	101	23.0	950	15.8
Never	3305	51.3	215	48.9	3090	51.5
Marital status							.22
Unmarried	755	11.7	60	13.6	695	11.6
Married	5690	88.3	380	86.4	5310	88.4
family history of mental illness							1.00
Yes	70	1.1	5	1.1	65	1.1
No	6375	98.9	435	98.9	5940	98.9
Insomnia							<.001
Yes	1103	17.1	157	35.7	946	15.8
No	5342	82.9	283	64.3	5059	84.2
Hypertension							0.04
Yes	4374	67.9	319	72.5	4055	67.5
No	2071	32.1	121	27.5	1950	32.5
Stroke							<.001
Yes	1286	20.0	141	32.0	1145	19.1
No	5159	80.0	299	68.0	4860	80.9
Diabetes mellitus							0.02
Yes	1770	27.5	142	32.3	1628	27.1
No	4675	72.5	298	67.7	4377	72.9
PM2.5 (median [IQR])^e	55.0	[47.3, 68.1]	55.5	[47.0, 65.4]	55.0	[47.3, 68.1]	1.00
Region							0.23
East China	4902	76.1	348	79.1	4554	75.8
Central China	562	8.7	37	8.4	525	8.7
West China	981	15.2	55	12.5	926	15.4
Total	6445	100.0	440	6.8	6005	93.2

Abbreviations: SD, standard deviation; PM_2.5, particulate matter with an aerodynamic diameter ≤2.5 μm; IQR, interquartile range.

^aStudent’s t-test was used to examine the difference between veterans with and without depression as the variable was normal.

^bChi-squares test was used to examine the difference between veterans with and without depression.

^cRegular physical activity was defined as exercising at least 30 minutes per day at an intensity equal to or greater than walking.

^dRegular social activity was defined as participating in organized activities involving social contact.

^eKruskal-Wallis test was used to examine the difference between veterans with and without depression as the variable was not normal.

Table 2. A summary of participants’ exposure to outdoor LAN (nW/cm²/sr) during the 1 year before the investigation.

Variables	Overall		Depressive symptoms cases		Controls
	Median	IQR	Median	IQR	Median	IQR
Age
<80	65.77	55.45	79.67	45.46	65.77	56.45
≥80	65.43	52.08	72.17	56.45	65.43	51.75
Years of education
≤9	64.67	51.75	70.89	53.14	64.41	51.59
>9	66.68	56.45	83.90	54.64	66.68	56.61
Regular physical activities
Yes	65.77	53.29	77.23	53.42	65.43	53.29
No	64.40	51.70	70.89	54.68	64.31	51.55
Regular social activities
Yes	66.88	52.50	85.27	52.70	65.77	51.43
No	64.67	53.67	86.64	52.24	66.16	50.24
Smoking
Yes	62.22	58.39	82.93	49.66	61.13	59.27
No	65.77	53.29	74.16	54.68	65.43	52.87
Drinking
Yes	65.43	53.05	77.53	63.26	65.43	52.34
No	65.43	53.29	74.16	50.16	65.43	53.29
Marital status
Unmarried	64.41	52.34	70.27	59.86	64.41	52.34
Married	65.43	53.29	77.23	55.75	65.43	53.42
Total	65.43	53.42	75.22	53.41	65.43	52.59

Abbreviations: IQR, interquartile range.

Figure 2. The ORs and 95%CIs of depressive symptoms for stratified analyses associated with per IQR increase in outdoor LAN exposure during the 1 year before the investigation.

Abbreviations: OR, odds ratio; CI, confidence interval.

Models were adjusted for age, years of education, family history of mental illness, physical activities, social activities, smoking, drinking, marital status, insomnia, PM_2.5, and history of diabetes, hypertension, stroke, and region of each community (East China, West China, Central China) as a random-effect term. Age was included in the adjusted model as a smooth term with 4 degrees of freedom. PM_2.5 was divided into low and high groups according to the median.

Table 3. The ORs and 95%CIs of depressive symptoms associated with exposure to outdoor LAN during the 1 year before the investigation in crude and adjusted models.

Outdoor LAN	OR (95%CI)
	Crude model ^a	Adjusted model ^b
Low level (median 30.75 nW/cm^2/sr)	Reference	Reference
Middle level (median 64.67 nW/cm^2/sr)	1.17 (0.91, 1.50)	1.14 (0.88, 1.47)
High level (median 107.73 nW/cm^2/sr)	1.34 (1.05, 1.72)	1.49 (1.15, 1.92)
P for trend^c	0.02	<.01
Continuous LAN (per IQR increase ^d)	1.15 (1.00, 1.32)	1.22 (1.06, 1.40)

Abbreviations: LAN, light at night; OR, odds ratio; CI, confidence interval; IQR, interquartile range.

^aModels included outdoor LAN exposure and region of each community (East China, Central China, and West China) as a random-effect term.

^bModels were additionally adjusted for age, years of education, family history of mental illness, physical activities, social activities, smoking, drinking, marital status, insomnia, PM_2.5, and history of diabetes, hypertension, stroke, and region of each community (East China, West China, Central China) as a random-effect term. Age was included in the adjusted model as a smooth term with 4 degrees of freedom. PM_2.5 was divided into low and high groups according to the median.

^cTest for the trend is based on the median value for each level.

^dIQR = 53.42 nW/cm²/sr.

Figure 3. The ORs and 95%CIs of depressive symptoms at different levels of LAN exposure against the lowest level and those associated with per IQR (53.42 nW/cm²/sr) increase in LAN during different exposure periods.

Abbreviations: OR, odds ratio; CI, confidence interval.

Models were adjusted for age, years of education, family history of mental illness, physical activities, social activities, smoking, drinking, marital status, insomnia, PM_2.5, and history of diabetes, hypertension, stroke, and region of each community (East China, West China, Central China) as a random-effect term. Age was included in the adjusted model as a smooth term with 4 degrees of freedom. PM_2.5 was divided into low and high groups according to the median.