Table 2.

Subgroup analyses by different exposure windows for the association between solar UVR exposure and the risk of developing breast cancer.

Subgroup	Estimates ($n$)	Relative risk (95% CI)	$I^2$ (%)
$\ge 1\mathrm{h}/\mathrm{d}$ vs. $<1\mathrm{h}/\mathrm{d}$
Adolescence	3	0.83 (0.71, 0.98)	78.5
Later in life ($\ge 45\text{\hspace{0.17em} years}$ of age)	4	0.97 (0.85, 1.11)	55.2
Dose–response
Adolescence
1 to $<2\mathrm{h}$ vs. $<1\mathrm{h}$	3	0.88 (0.79, 0.99)	0.0
$\ge 2\mathrm{h}$ vs. $<1\mathrm{h}$	3	0.72 (0.65, 0.80)	0.0
Later in life ($\ge 45\text{\hspace{0.17em} years}$ of age)
1 to $<2\mathrm{h}$ vs. $<1\mathrm{h}$	4	1.00 (0.86, 1.16)	54.0
$\ge 2\mathrm{h}$ vs. $<1\mathrm{h}$	4	0.94 (0.85, 1.04)	5.7
Ambient UVR (high exposure vs. low exposure)
Adolescence	4	0.99 (0.84, 1.17)	54.8
Later in life ($\ge 45\text{\hspace{0.17em} years}$ of age)	2	1.07 (0.77, 1.48)	67.3

Note: Relative risk estimates for each subgroup were estimated with DerSimonian and Laird random-effect models. UVR, ultraviolet radiation.