Cold Climate Is a Risk Factor for Thyroid Cancer.

BACKGROUND The incidence rates of differentiated thyroid cancers of all sizes increased between 1988 and 2005 in both men and women. Exposure to ionizing radiation is the best-established environmental risk factor for thyroid cancer. Nonionizing radiation from cell phones has also been implicated. A positive correlation between all-cancer incidence rates and latitude and an inverse correlation between all-cancer incidence rates and temperature have been reported. In the present study, we examined the relationship between thyroid cancer incidence and average temperature in 50 U.S. states. METHODS The age-adjusted incidence of thyroid cancer is from U.S. Cancer Statistics Working Group, United States Cancer Statistics: 1999-2010, Incidence and Mortality Web-based Report (Atlanta: Department of Health and Human Services, Centers for Disease Control and Prevention and National Cancer Institute; 2013, available at: www.cdc.gov/uscs). Average temperature by state is from the National Climatic Data Center, National Oceanic and Atmospheric Administration (http://www.ncdc.noaa.gov). Information on high-impact exposure to nuclear radiation by state is from the National Radiation Exposure Screening and Education Program, U.S. Health Resources and Services Administration (http://www.hrsa.gov/gethealthcare/conditions/radiationexposure). Cell-phone subscriber data for 2007 is from the Governing State and Local Sourcebook (http://sourcebook.governing.com). Mean elevation and latitude of U.S. states is from "Elevations and Distances in the United States," Reston, VA: U.S. Geological Survey, April 29, 2005 (http://pubs.er.usgs.gov). RESULTS There was a significant negative correlation between average temperature by state and the age-adjusted incidence of all thyroid cancers (r2 = -0.212, P = 0.001). Because of the possible effects of ionizing radiation exposure from nuclear testing and nonionizing radiation exposure from cell phones, multiple linear regression analysis was performed. The analysis was done only for all thyroid cancers and for thyroid cancers in whites. The data from blacks and Hispanics were too fragmentary to analyze. In all thyroid cancers and thyroid cancers in whites, there was a significant negative correlation between average temperature and incidence that was unrelated to nuclear testing, cell-phone use, altitude, and latitude and was independent of the significant correlation of cell-phone subscriptions per population with thyroid cancer in whites. CONCLUSIONS Living in a cold-climate state, such as Alaska, doubles the risk of thyroid cancer as compared with a warm state such as Texas. Because of climate change, a significantly raised risk of heat-related and cold-related mortality is expected in the years to come. The elderly will be most at risk. No doubt, incidence patterns of thyroid cancer and other cancers may be affected.