Table 2.

Associations between cumulative average outdoor LAN and breast cancer in the Nurses’ Health Study II ($n=\mathrm{109,672}$) with 3,549 breast cancer cases over 2,187,425 person-years of follow-up (1989–2013).

Exposure	Cumulative average light at night
	Cases (n)	Person-years	Age-adjusted HR (95% CI)	Fully adjusted HR (95% CI)a
LAN quintile 1 (Median $4.3{\text{nW}/\mathrm{cm}}^2/\text{sr}$)	571	360,609	Reference	Reference
LAN quintile 2 (Median $12.4{\text{nW}/\mathrm{cm}}^2/\text{sr}$)	715	432,584	1.08 (0.97, 1.21)	1.05 (0.94, 1.18)
LAN quintile 3 (Median $22.9{\text{nW}/\mathrm{cm}}^2/\text{sr}$)	710	459,789	1.05 (0.94, 1.17)	1.01 (0.90, 1.13)
LAN quintile 4 (Median $37.2{\text{nW}/\mathrm{cm}}^2/\text{sr}$)	776	469,624	1.12 (1.01, 1.25)	1.08 (0.97, 1.22)
LAN quintile 5 (Median $64.0{\text{nW}/\mathrm{cm}}^2/\text{sr}$)	777	464,820	1.13 (1.02, 1.26)	1.14 (1.01, 1.29)
p for trendb			0.03	0.02
Continuous LAN (per IQR increasec)			1.03 (0.99, 1.07)	1.05 (1.00, 1.11)

Note: BMI, body mass index; CI, confidence interval; HR, hazard ratio; IQR, interquartile range; LAN, light at night; PM_2.5, particulate matter with aerodynamic diameter $<2.5\mathrm{\mu }\mathrm{m}$.

^aHRs are adjusted for benign breast disease history, family history of breast cancer, age at menarche, parity and age at first birth, height, white race, BMI, BMI at age 18, oral contraceptive use, mammography screening, menopausal status, smoking status, alternative healthy eating index, physical activity, marital status, living alone, personal income, shift work after 1989, region, ${\text{PM}}_{2.5}$, census-tract median home value, income, and population density.

^bTest for trend is based on the median value for each quintile.

^cAn IQR increase in cumulative average LAN is $31.6{\text{nW}/\mathrm{cm}}^2/\text{sr}$.