Table 3

HR of incident rheumatoid arthritis, according to cumulative average UV-B exposure in NHS and NHSII

 Cumulative average UV-B*
LowMediumHighp Trend
NHS
 Median UV-B104113164
 RA cases/person-years374/1 038 261340/1 120 965219/739 207
 Age-adjusted HR (95% CI)1.0 (ref)0.84 (0.73 to 0.98)0.79 (0.67 to 0.93)0.004
 Multivariable-adjusted HR† (95% CI)1.0 (ref)0.84 (0.73 to 0.98)0.79 (0.66 to 0.94)0.005
NHSII
 Median UV-B104113145
 RA cases/person-years101/600 134108/558 559172/883 582
 Age-adjusted HR (95% CI)1.0 (ref)1.10 (0.84 to 1.45)1.12 (0.87 to 1.43)0.39
 Multivariable-adjusted HR† (95% CI)1.0 (ref)1.04 (0.79 to 1.37)1.12 (0.87 to 1.44)0.37
  • *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.