Table 1.

Characteristics of eligible studies investigating the association between exposure to solar ultraviolet radiation and breast cancer risk.

Article	Country	Sample size (cases)	Exposure	Adjustments	Study quality (star rating)
John 2007[20]	USA	4183 (2054)	Self-reported lifetime outdoor activity	Age, race/ethnicity, education, family history of breast cancer, personal history of benign breast disease, age at menarche, number of full-term pregnancies, breastfeeding, body mass index, height, physical activity, and alcohol consumption	∗∗∗∗∗∗∗∗
Knight 2007[21]	Canada	2107 (972)	Time spent outdoors	Reference age, ethnicity, family history in first-degree relatives, ever breast-fed, education, age menarche, and age at first birth	∗∗∗∗∗∗∗∗
Blackmore 2008[22]	Canada	1894 (759)	Outdoor activity	Age, ethnicity, family history, ever breastfed, education, age menarche, age at first birth	∗∗∗∗∗∗∗∗
Aderson 2011[23]	Canada	6521 (3101)	Time spent in the sun	Age, marital status, education, ethnicity,body mass index,smoking status and packyears, breastfeeding, lactation, age at menarche, Oral Contraceptive use, Oral Contraceptive duration,parity, age at first live birth, age at last menstruation, duration of Hormone Replacement Therapy 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	∗∗∗∗∗∗∗∗
Bidgoli 2014[24]	Iran	176 (60)	Daily sunlight exposure	Not specified	∗∗∗∗∗∗∗
Qin 2019[25]	USA	1402 (1015)	Time spent outdoors	Age, education, age at menarche, menopausal status, age at first birth, ever breastfeeding, first-degree family history of breast cancer, history of benign breast disease, body mass index, vigorous physical activity, total energy intake, and total vitamin D intake.	∗∗∗∗∗∗∗∗