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. ---- 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-ti... 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