Rotating night shifts and risk of skin cancer in the nurses' health study.

Night shift work is associated with increased risk of several cancers, but the risk of skin cancer among night shift workers is unknown. We documented 10,799 incident skin cancers in 68,336 women in the Nurses' Health Study from June 1988 to June 2006 and examined the relationship between rotating night shifts and skin cancer. We used Cox proportional hazard models, adjusted for confounding variables (phenotypic and established risk factors of skin cancer), and performed stratified analysis to explore the modifying effect of hair color. Working 10 years or more on rotating night shifts was associated with a 14% decreased risk of skin cancer compared with never working night shifts (age-standardized incidence rate: 976 per 100,000 person-years (PY) vs 1070 per 100,000 PY, respectively; adjusted hazard ratios = 0.86, 95% confidence interval = 0.81 to 0.92, P(trend) < .001). This association was strongest for cutaneous melanoma; working 10 years or more of rotating night shifts was associated with 44% decreased risk of melanoma, after adjustment for melanoma risk factors (age-standardized incidence rate: 20 per 100,000 PY vs 35 per 100,000 PY, respectively; adjusted hazard ratios = 0.56, 95% confidence interval = 0.36 to 0.87, P(trend) = .005). Hair color, a surrogate for an individual's susceptibility to skin cancer, was a statistically significant effect modifier for the observed associations; darker-haired women had the lowest risk (P(interaction) = .02).