The 2017 Nobel Prize in medicine was awarded to scientists for their research on circadian rhythm, some times referred to as the biological clock. Circadian disruption has been found to be a probable human carcinogen. Much of the work in this area has focused on shift workers who work nights and sleep during the day.
But new research suggests the problem may be far greater and affect a large number of people. Mikhail Borisenkow of the Russian Academy of Science first postulated that the risk of cancer would be greater at the far western edge of time zones than would be the case on the eastern edge of time zones where sunrise can be an hour earlier. Many people in the eastern regions of time zones awaken from a night’s sleep after sunrise. But people in the western region may get up at the same time on the clock to start their day, but it is dark when they get up. This is a disruption in their natural circadian rhythm.
A new paper by researchers at the National Cancer Institute has tested this hypothesis in the United States. They 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. All told, 4 million cancer diagnoses in residents of 607 counties in 11 U.S. states were examined.
The results showed that there indeed was increased risk from east to west within a time zone for total and for many specific cancers. This included increased risk of cancers of the esophagus, colorectum, lung, breast, and uterus in women.
The researchers concluded: “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.”
The study, “Longitude Position in a Time Zone and Cancer Risk in the United States,” was published in the journal Cancer Epidemiology, Biomarkers & Prevention. It may be accessed here.