Table 3.

Stratum-specific hazard ratios (HRs), 95% confidence intervals (CIs), and p-values for test of heterogeneity for the association between 25-hydroxyvitamin D [25(OH)D] (4th quartiles vs. quartiles 1–3) and breast cancer within 5 y.

Characteristic	Cases; $n$ (%)	Subcohort; $n$ (%)	Quartile 1–3 $\le 38.0\text{ng}/\mathrm{mL}$	Quartile 4 $>38.0\text{ng}/\mathrm{mL}$	p-Value for heterogeneity
Age, ya
35–59	946 (59)	1,248 (69)	1.00	0.92 (0.72, 1.17)	0.01
$\ge 60$	654 (41)	574 (32)	1.00	0.62 (0.49, 0.78)
Menopausal statusa
Premenopausal	465 (29)	610 (33)	1.00	0.94 (0.63, 1.41)	0.02
Postmenopausal	1,135 (71)	1,212 (67)	1.00	0.70 (0.58, 0.85)
Race
Non-African Americans	1,479 (92)	1,690 (93)	1.00	0.75 (0.63, 0.90)	0.90
African Americans	121 (8)	132 (7)	1.00	0.89 (0.30, 2.64)
Obese ($\text{BMI}\ge 30\mathrm{kg}\mathrm{/}{\mathrm{m}}^2$)
No	1,089 (68)	1,279 (70)	1.00	0.83 (0.69, 1.01)	0.04
Yes	511 (32)	543 (30)	1.00	0.45 (0.30, 0.69)
Current hormone therapy user
No	1,384 (87)	1,632 (90)	1.00	0.78 (0.65, 0.94)	0.12
Estrogen plus progestin	84 (5)	66 (4)	1.00	1.92 (0.84, 4.42)
Estrogen only	132 (8)	124 (7)	1.00	0.44 (0.23, 0.83)
Regular vitamin D supplementation
No	733 (47)	838 (47)	1.00	0.62 (0.45, 0.84)	0.14
Yes	839 (53)	945 (53)	1.00	0.83 (0.67, 1.04)
Dietary intake of vitamin D
$0–120\text{IU}/\mathrm{d}$	760 (48)	876 (49)	1.00	0.77 (0.60, 0.99)	0.69
$>120\text{IU}/\mathrm{d}$	812 (52)	907 (51)	1.00	0.74 (0.58, 0.94)
Time spent outdoors
$0–546\mathrm{h}/\mathrm{y}$	830 (52)	898 (50)	1.00	0.73 (0.56, 0.94)	0.69
$>546\mathrm{h}/\mathrm{y}$	766 (48)	914 (50)	1.00	0.80 (0.63, 1.02)
Latitude of primary residence
0–39°	823 (52)	949 (52)	1.00	0.84 (0.66, 1.07)	0.07
$>39°$	775 (48)	868 (48)	1.00	0.66 (0.51, 0.85)
Physical activity
$0–2\mathrm{h}/\mathrm{wk}$	788 (49)	931 (51)	1.00	0.69 (0.52, 0.90)	0.76
$>2\mathrm{h}/\mathrm{wk}$	818 (51)	891 (49)	1.00	0.78 (0.63, 0.97)

Note: All models are adjusted for age, season, batch, race, education level, current hormonal birth control use, current hormone therapy type, menopausal status, physical activity, body mass index (BMI), osteoporosis, parity, alcohol consumption, and a BMI × menopausal status interaction term. IU, international units.

^aAge and menopausal status allowed to vary over time in the model. The provided frequencies are for age and menopausal status at the baseline interview. Menopausal status is based on information from both baseline and follow-up interviews.