Table 3.

Interactions between cumulative UV flux and potential risk factors of skin cancer in the Nurses' Health Study II (1989–2009)

BCCSCCMelanoma
CasesPerson-years (thousands)MV-adjusted RRa (95% CI)P for interactionbCasesPerson-years (thousands)MV-adjusted RRa (95% CI)P for interactionbCasesPerson-years (thousands)MV-adjusted RRa (95% CI)P for interactionb
Family history of melanoma
 No577818051.0074717881.0060418041.00
 Yes11772471.37 (1.28–1.46)0.0061332431.17 (0.97–1.41)0.9471752461.80 (1.52–2.13)0.561
Natural hair color
 Red432681.51 (1.36–1.67)62661.56 (1.18–2.05)59681.97 (1.48–2.63)
 Blonde12432901.13 (1.06–1.21)1552861.09 (0.90–1.32)1642901.27 (1.05–1.54)
 Light brown24917041.003306961.002897031.00
 Dark brown20166930.89 (0.84–0.94)2696870.90 (0.76–1.06)2026920.77 (0.65–0.93)
 Black79300.92 (0.74–1.15)0.0543300.27 (0.09–0.84)0.2993300.32 (0.10–1.01)0.162
Number of moles on legs
 None29709861.004299781.002439871.00
 1–212793761.10 (1.03–1.17)1523720.90 (0.75–1.09)1233761.29 (1.04–1.60)
 3–911873351.13 (1.06–1.21)1343320.87 (0.72–1.06)1543351.81 (1.47–2.21)
 ≥1012442821.35 (1.26–1.44)0.4191322790.99 (0.81–1.20)0.9702322813.04 (2.54–3.65)0.555
Sunburn reaction as a child/adolescent
 None/some redness275610701.0033410621.0031610691.00
 Burn18944901.37 (1.29–1.45)2214841.36 (1.14–1.62)2124891.24 (1.04–1.48)
 Painful burn/blisters22914881.60 (1.50–1.70)0.2763254811.93 (1.63–2.28)0.0332514881.36 (1.14–1.63)0.385
Number of blistering sunburns between ages 15–20
 None16906861.002136821.001816851.00
 1–4417211601.30 (1.23–1.38)51711481.25 (1.06–1.47)46311601.32 (1.11–1.57)
 ≥510751981.68 (1.55–1.82)<0.0011431941.68 (1.34–2.11)0.7451311981.80 (1.42–2.28)0.210
Average tanning bed use in early life (high school and ages 25–35)
 None400510981.0054910861.0049410981.00
 1–2 times/mo8432081.19 (1.10–1.28)1302051.48 (1.22–1.79)942081.01 (0.81–1.27)
 3–5 times/mo262671.20 (1.06–1.37)43661.65 (1.21–2.26)37671.27 (0.90–1.77)
 ≥6 times/mo382801.59 (1.43–1.77)0.60950791.78 (1.33–2.39)0.75941791.24 (0.89–1.71)0.094
Body mass index, kg/m2
 <24.9395411031.0051110911.0045911031.00
 25–29.917485110.81 (0.77–0.86)2385070.79 (0.68–0.92)1805110.81 (0.68–0.96)
 30–34.97372440.69 (0.64–0.75)812420.53 (0.42–0.68)732440.70 (0.54–0.90)
 ≥354991880.60 (0.54–0.66)0.358491860.41 (0.30–0.55)0.621661880.83 (0.63–1.09)0.322
Smoking status
 No437913171.0050813051.0051113161.00
 Past19544921.06 (1.00–1.12)2764861.20 (1.04–1.40)2114920.99 (0.84–1.17)
 Current 1–14 cigs/d286940.96 (0.85–1.08)52931.48 (1.11–1.97)25940.69 (0.46–1.03)
 Current 15–24 cigs/d205750.93 (0.80–1.07)30751.18 (0.81–1.70)22750.82 (0.54–1.27)
 Current ≥25 cigs/d78310.88 (0.71–1.11)0.1879300.89 (0.46–1.73)0.6047310.67 (0.32–1.42)0.363
Alcohol intake, g/d
 018086111.002316051.002116111.00
 <5.019585601.14 (1.07–1.22)2685531.18 (0.99–1.41)2365591.18 (0.98–1.42)
 5.0–9.97111721.15 (1.06–1.26)961701.11 (0.87–1.41)811721.20 (0.93–1.56)
 ≥1010401911.31 (1.21–1.41)0.1051481881.23 (0.99–1.53)0.7771161911.47 (1.16–1.86)0.058
Physical activity, metabolic equivalent hours/week
 <3.08952891.001232861.001112891.00
 3.0–8.912063871.05 (0.96–1.15)1633821.06 (0.84–1.34)1423860.94 (0.74–1.21)
 9.0–17.912633631.10 (1.01–1.20)1663591.08 (0.85–1.36)1343630.93 (0.72–1.19)
 18.0–26.98542251.15 (1.05–1.27)1132231.12 (0.86–1.45)1022251.11 (0.84–1.45)
 ≥27.018214281.23 (1.14–1.34)0.6872434231.24 (0.99–1.55)0.6032194271.25 (0.99–1.58)0.072
Rotating night shifts
 Never15064341.001994291.001764331.00
 1–2 years13423870.97 (0.90–1.05)1833821.00 (0.82–1.23)1683871.03 (0.83–1.27)
 3–9 years14384400.91 (0.85–0.98)1884350.91 (0.75–1.12)2064401.11 (0.90–1.36)
 ≥10 years291850.85 (0.75–0.96)0.37245840.94 (0.68–1.31)0.97637850.98 (0.69–1.41)0.279
Menopausal status
 Premenopause405414091.0044513931.0053814071.00
 Postmenopause20733510.92 (0.85–0.99)0.6883253481.05 (0.86–1.28)0.6411723521.01 (0.80–1.27)0.233

NOTE: Bold indicates P < 0.05.

  • aBased on multivariable analysis controlled for covariates listed in Table 2 (footnote b).

  • bWe tested the significance of the interaction with a likelihood ratio test by comparing a model with the main effects of cumulative UV flux and the stratifying variable and their interaction terms with a reduced model with only the main effects.