Table 1.

Characteristics of all studies investigating the association of solar UVR with the risk of breast cancer ($n=14$).

Reference	Country	Study design	Sample size [case/controls (n/n)]	Age (y)	Exposures	Exposure windowa	Subgroup analyses	Confounders
Zamoiski et al. 2016	USA	Cohort	716/36,009	40–70	Ambient, time spent in the sun, combined UVR	0–12, 13–19, 20–39, 40–64, $>65$	None	Age, race, BMI, ever given birth, exercise, age at first birth, age at menarche, HRT, family history, menopause, number of births, OC use, alcohol consumption, ionizing radiation to the breast
Cauchi et al. 2016	Malta	Case–control	200/403	20–80	Time spent in the sun	lifetime	None	Diet, OC use, menopausal status, history of myocardial infarction, height, family history of breast cancer
Engel et al. 2014	USA (IA and NC)	Cohort	578/32,127	18–86	Time spent in the sun	Enrollment, 10 y before enrollment	ER/PR status, menopausal status	Age, race, menopause, combined parity and age at first birth, family history of breast cancer
Bidgoli and Azarshab 2014	Iran	Case–control	60/116	20–40	Amount of time spent outdoors, coverage of body from sunlight	Lifetime	None	Not specified
Lin et al. 2012	USA (CA, FL, LA, NJ, NC, PA, GA, MI)	Cohort	8,681/178,138	50–75	Ambient UVR	Baseline to end of follow-up	None	Age, BMI, caloric intake, intake of fruit and vegetables, red and white meat, alcohol consumption, tobacco smoking, education, physical activity, and median household income
Yang et al. 2011b	Sweden	Cohort	2,303/49,261	50–60	Number of weeks spent on sunbathing vacations, solarium use	10–19, 20–29, 30–39	None	Education, smoking, alcohol, BMI, physical activity, parity, age at first birth, age at menarche, OC use, breast feeding, family history of breast cancer
Engel et al. 2011	France	Cohort	2,871/67,721	42–72	Ambient, place of residence	Baseline to end of follow-up	Menopausal status	Menopausal status, BMI, PA, age at menopause, age at menarche, OC use, use of HRT, calcium intake, use of calcium supplement, alcohol, total energy intake–alcohol, university degree, family history, sunburn resistance, skin complexion
Anderson et al. 2011b	Canada (ON)	Case–control	3,101/3,420	$\text{Mean \hspace{0.17em} age}=56$	Time spent in the sun, ambient UVR, solar vitamin D score	Teen years, 20s–30s, 40s–50s, 60s–75	None	Age, marital status, education, ethnicity, BMI, smoking status and pack-years, breastfeeding, lactation, age at menarche, OC use, OC duration, parity, age at first live birth, age at last menstruation, duration of HRT use, history of benign breast disease, family history of breast cancer, screening mammogram, alcohol intake, fat intake, calorie intake, physical activity, phytoestrogen intake, vitamin D and calcium intake
Edvardsen et al. 2011	Norway	Cohort	948/41,181	50–60	Ambient (VD dose), sun-seeking holidays, solarium use	Lifetime	None	Age, BMI, alcohol, parity, OC use, menopausal status, hormone therapy, age at first birth, mammography frequency
Millen et al. 2009	USA (23 states and DC)	Cohort	2,535/71,662	50–80	Region of residence over life periods, reported time spent in the sun	Study follow-up from 1993–1998 to 2006	ER/PR status for ambient	Age, race, education, weight, family history, age at menarche, age at menopause, parity, age at first birth, HRT, alcohol, physical activity
Blackmore et al. 2008	Canada (ON)	Case–control	759/1,135	$\text{Mean \hspace{0.17em} age}=54$	Time spent outdoors	10–19, 20–29, 45–54	ER/PR status	Age, ethnicity, family history, ever breastfed, education, age menarche, age at first birth
John et al. 2007	USA (San Francisco Bay)	Case–control	2,054/2,129	35–80	Self-reported lifetime outdoor activity	Lifetime	Localized vs. advanced	Age, race, education, family history, personal history of benign breast disease, number of full-term pregnancies, breastfeeding, height, alcohol consumption, BMI, menopausal status, HRT
Knight et al. 2007	Canada (ON)	Case–control	972/1,135	40–65	Time spent outdoors	10–19, 20–29, 45–54	None	Age, ethnicity, family history, ever breastfed, education, age menarche, age at first birth
John et al. 1999	USA	Cohort	190/5,009	25–74 at baseline	Recreational, occupational time spent in the sun, combined recreational and occupational UVR exposure, ambient UVR	Follow-up from 1971–1975 to 1992	None	Age, education, age at menarche, age at menopause, BMI, frequency of alcohol consumption, physical activity

Note: BMI, body mass index; CA, California; DC, District of Columbia; FL, Florida; GA, Georgia; HRT, hormone replacement therapy; IA, Iowa; LA, Louisiana; MI, Michigan; NC, North Carolina; NJ, New Jersey; OC, oral contraceptives; ON, Ontario; PA, Pennsylvania; USA, United States of America; UVR, ultraviolet radiation; VD, vitamin D.

^aNumber ranges correspond to years of age.

^bStudy was not included in quantitative meta-analysis because the exposures did not match those within the current study.