Longitude Position in a Time Zone and Cancer Risk in the United States.

Background: Circadian disruption is a probable human carcinogen. From the eastern to western border of a time zone, social time is equal, whereas solar time is progressively delayed, producing increased discrepancies between individuals' social and biological circadian time. Accordingly, western time zone residents experience greater circadian disruption and may be at an increased risk of cancer.
Methods: We examined associations between the position in a time zone and age-standardized county-level incidence rates for total cancers combined and 23 specific cancers by gender using the data of the Surveillance, Epidemiology, and End Results Program (2000-2012), including four million cancer diagnoses in white residents of 607 counties in 11 U.S. states. Log-linear regression was conducted, adjusting for latitude, poverty, cigarette smoking, and state. Bonferroni-corrected P values were used as the significance criteria.
Results: Risk increased from east to west within a time zone for total and for many specific cancers, including chronic lymphocytic leukemia (both genders) and cancers of the stomach, liver, prostate, and non-Hodgkin lymphoma in men and cancers of the esophagus, colorectum, lung, breast, and corpus uteri in women.Conclusions: Risk increased from the east to the west in a time zone for total and many specific cancers, in accord with the circadian disruption hypothesis. Replications in analytic epidemiologic studies are warranted.Impact: Our findings suggest that circadian disruption may not be a rare phenomenon affecting only shift workers, but is widespread in the general population with broader implications for public health than generally appreciated. Cancer Epidemiol Biomarkers Prev; 26(8); 1306-11. ©2017 AACR. ©2017 American Association for Cancer Research.