[tz] Time zones, daylight saving, and cancer risk

[Paul Eggert]

In 2011 Mikhail Borisenkov of the Komi Science Center in Syktyvkar, Russia 
reported that latitude and longitude can affect cancer rates. In particular he 
found that in Russia, position within a time zone explained 15% of the 
variability in female breast cancer mortality.

Similar results have now been reported in the US. Neil Caporaso and colleagues 
at the National Cancer Institute in Bethesda, Maryland recently found a 
significant association between time zone position and cancer incidence. They 
estimated that the risk of breast cancer is 12% higher at the western extreme of 
a US time zone compared to the eastern extreme. Other cancers show similar (but 
smaller) effects.

A plausible explanation is that ill-timed light increases cancer risk by 
disrupting circadian rhythm. This effect has been known for some time in other 
respects: for example, blind women have a significantly lower risk for breast 
cancer, possibly because melatonin offers a protective effect and nocturnal 
exposure to visible light suppresses melatonin secretion. This is currently an 
active area of research: the 2017 Nobel Prizes in Physiology or Medicine went to 
circadian-rhythm researchers.

Perhaps we should not take Ben Franklin's "early to bed and early to rise" 
advice to an extreme, as daylight saving time (or more generally, moving time 
zones eastward) can significantly increase cancer risk.

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Stevens RG. Breast cancer risk higher in western parts of time zones; is 
electric light to blame? The Conversation. 2017-10-19. 
https://theconversation.com/breast-cancer-risk-higher-in-western-parts-of-time-zones-is-electric-light-to-blame-85803

Gu F, Xu S, Devesa SS et al. Longitude position in a time zone and cancer risk 
in the United States. Cancer Epidem Biomarkers Prev. 2017-08-01;26(8):1306-11 
http://dx.doi.org/10.1158/1055-9965.EPI-16-1029

Borisenkov MF. Latitude of residence and position in time zone are predictors of 
cancer incidence, cancer mortality, and life expectancy at birth. Chronobiology 
Int. 2011-01-13;28(2):155-62. http://dx.doi.org/10.3109/07420528.2010.541312