Natural Radiation Exposure and Carotid Intima-Media Thickness Among Women in Karunagappally, Kerala, India.

Background A cross-sectional study was conducted to examine the relationship between natural radiation exposure and intima-media thickness (IMT), an atherosclerosis indicator, among female residents in Karunagappally, Kerala, South India, which is known to have areas with high natural background radiation (HNBR) derived mainly from thorium. Methods Cumulative radiation doses received during childhood, adulthood, and entire life were estimated on the basis of annual indoor and outdoor radiation doses and hours spent indoors and outdoors. In 2013–2014, IMT of the carotid artery was measured with ultrasonography among 400 women aged 29–60 years in Karunagappally. Since there were three subjects with outlying maximum IMT values, corrected IMT values excluding those outliers were calculated. For statistical analysis, raw and corrected IMT values were used. Results The regression analysis adjusting for age and religion showed a statistically significant association of mean and maximum IMT with radiation. The most strongly related radiation dose was with the adult dose. Its association with IMT became stronger when paediatric dose was also taken into account. When adjusted for fasting blood sugar and HbA1c, adult dose was statistically significantly related to raw mean IMT (P = 0.008) and corrected mean IMT (P = 0.018). Maximum IMT values were also related to adult doses but the association was not statistically significant (raw maximum IMT, P = 0.061 and corrected maximum IMT, P = 0.138). Conclusions Among female residents in the HNBR areas in south India, mean IMT statistically significantly increased in relation to the adult dose. Further studies are necessary to evaluate the causal association of the observation.