Table 4

HR of incident rheumatoid arthritis according to UV-B exposure at birth and at age 15 in NHS and NHSII

 UV-B* at Birth
LowMediumHighp Trend
NHS
 Median UV-B104113145
 RA cases/person-years373/907 481326/968 621104/328 171
 Age-adjusted HR (95% CI)1.0 (ref)0.82 (0.70 to 0.95)0.76 (0.61 to 0.95)0.003
 Multivariable-adjusted HR† (95% CI)1.0 (ref)0.82 (0.70 to 0.95)0.77 (0.62 to 0.97)0.005
NHSII
 Median UV-B104113144
 RA cases/person-years111/561 772114/567 58497/520 394
 Age-adjusted HR (95% CI)1.0 (ref)1.00 (0.77 to 1.30)0.95 (0.72 to 1.25)0.72
 Multivariable-adjusted HR† (95% CI)1.0 (ref)0.95 (0.73 to 1.24)0.91 (0.69 to 1.20)0.48
UV-B* at Age 15
LowMediumHighp Trend
NHS
 Median UV-B104113154
 RA cases/person-years379/147 027320/168 257107/54 650
 Age-adjusted HR (95% CI)1.0 (ref)0.74 (0.64 to 0.86)0.79 (0.63 to 0.98)0.001
 Multivariable-adjusted HR† (95% CI)1.0 (ref)0.76 (0.65 to 0.89)0.84 (0.67 to 1.05)0.009
NHSII
 Median UV-B104113145
 RA cases/person-years101/559 317120/561 961105/548 576
 Age-adjusted HR (95% CI)1.0 (ref)1.16 (0.89 to 1.52)1.07 (0.81 to 1.40)0.65
 Multivariable-adjusted HR† (95% CI)1.0 (ref)1.11 (0.85 to 1.46)1.04 (0.78 to 1.37)0.82

  • *Low: ≤109 Robertson–Berger units×10−4 (R-B), medium: >109 to ≤117 R-B, high: >117 R-B.

  • †Adjusted for age, pack-years smoking, parity, breast feeding, physical activity, alcohol consumption, race, husband's education, census-tract median income, postmenopausal status and hormone use, mean number of rheumatologists per zip code.

  • HR, hazard ratio; RA, rheumatoid arthritis; UV-B, ultraviolet-B.