Table 2.

HRs and 95% CIs for incident breast cancer by region of residence at birth, age 15 y, age 35 y, and baseline (1993-1998); and solar irradiance values in Langleys and Watts: the WHIOS (n = 71,662)

ExposureBreast cancer casesnPerson-years of follow-up (×1,000)Annualized rate (%)Age-adjusted HR (95% CI)Multivariate model 1* HR (95% CI)Multivariate model 2 HR (95% CI)
Region at birth
    Southern45513,8191120.401.01.01.0
    Middle88523,9582040.431.08 (0.97-1.21)0.98 (0.87-1.10)0.98 (0.87-1.10)
    Northern1,01028,1182390.421.04 (0.94-1.17)0.95 (0.84-1.07)0.95 (0.84-1.07)
    Not United States1625,021410.390.97 (0.81-1.16)1.00 (0.83-1.20)1.00 (0.83-1.20)
Ptrend§0.630.410.40
Region at age 15 y§
    Southern43313,3251090.401.01.01.0
    Middle93225,1062130.441.11 (0.99-1.24)1.02 (0.90-1.14)1.02 (0.90-1.14)
    Northern1,02728,4022410.431.07 (0.95-1.20)1.00 (0.88-1.12)1.00 (0.88-1.12)
    Not United States1274,196340.370.93 (0.76-1.13)0.97 (0.79-1.19)0.97 (0.79-1.19)
Ptrend0.440.830.81
Region at age 35 y§
    Southern48513,7251130.431.01.01.0
    Middle1,02528,6992430.420.98 (0.88-1.09)0.92 (0.82-1.02)0.92 (0.82-1.02)
    Northern93226,1692210.420.96 (0.86-1.07)0.92 (0.82-1.03)0.92 (0.82-1.03)
    Not United States772,240180.420.96 (0.76-1.22)0.95 (0.75-1.21)0.95 (0.75-1.21)
Ptrend0.470.230.23
Region at baseline
    Southern86925,3542090.421.01.01.0
    Middle54813,8951180.461.12 (1.01-1.25)1.06 (0.95-1.18)1.06 (0.95-1.18)
    Northern1,11832,4132750.410.98 (0.89-1.07)0.97 (0.89-1.07)0.97 (0.89-1.07)
Ptrend0.360.910.92
Clinic center Langleys (gm-cal) per cm2
    475-50055515,3381270.441.01.01.0
    400-43043112,3391030.420.97 (0.85-1.10)0.93 (0.82-1.06)0.93 (0.82-1.06)
    375-3802998,009670.441.04 (0.90-1.20)1.00 (0.87-1.16)1.00 (0.87-1.16)
    35051815,2341270.410.93 (0.83-1.05)0.94 (0.83-1.06)0.94 (0.83-1.06)
    300-32573220,7421780.410.95 (0.85-1.06)0.93 (0.83-1.05)0.93 (0.83-1.05)
Ptrend0.460.290.29
Clinic center Watts (J/s) per m2
    1.5-1.9350 9,655800.441.01.01.0
    1.456216,3691360.410.93 (0.82-1.07)0.85 (0.74-0.97)0.85 (0.74-0.97)
    1.051913,2581110.471.06 (0.92-1.21)0.96 (0.83-1.10)0.96 (0.83-1.10)
    0.755615,7301350.410.95 (0.83-1.08)0.88 (0.77-1.02)0.88 (0.77-1.01)
    0.4-0.554816,6501400.390.89 (0.78-1.02)0.85 (0.74-0.98)0.85 (0.74-0.98)
Ptrend0.230.200.20
  • * Adjusted for age, race/ethnicity, education, weight, family history of breast cancer, age at menarche, age at menopause, parity, age at first birth, hormone therapy duration of use, alcohol intake, and recreational physical activity.

  • Adjusted for all covariates in multivariate model 1 plus adjustment for vitamin D intake from foods and supplements (energy adjusted IU/d).

  • Some persons were missing data for region of residence at birth, and ages 15 and 35 y. Total n for analyses by region of residence at birth is 70,916, at age 15 y is 71,029 and at age 35 y is 70,833.

  • § A test for trend was conducted using ordinal variable assigned to Southern, Middle and Northern for region at birth, age 15 and age 35 y (excluding those living outside the United States.). A test for trend was conducted using continuous variable for region at baseline, Langleys, and Watts.