Inhabitants of the high-level natural radiation areas (>1 mSv year(-1)) of Kerala in southwest India were evaluated for basal damage (spontaneous DNA strand breaks and alkali-labile sites) by the alkaline comet assay and oxidative DNA damage (ENDO III- and hOGG1-sensitive sites) by the enzyme-modified comet assay. Of the 67 adult male subjects studied, 45 were from high-level natural radiation areas and 22 subjects were from a nearby normal-level natural radiation area (≤1 mSv year(-1)). Basal damage due to the age and residential area (normal-level natural radiation area/high-level natural radiation areas) of the donors showed significant interaction (P < 0.001) when all subjects were analyzed using a general linear model (GLM). In subgroup analysis, basal damage increased with age in subjects from the normal-level natural radiation area (P = 0.02), while a significant negative correlation (P = 0.002) was observed in subjects from high-level natural radiation areas. Further, basal damage in elderly subjects from high-level natural radiation areas was significantly (P < 0.001) lower compared to the subjects from the normal-level natural radiation area. Oxidative DNA damage was not influenced by age, smoking habit or residential area in the entire sample. However, in a subgroup analysis, hOGG1-sensitive sites showed a significant increase with age in subjects from high-level natural radiation areas (P = 0.005). ENDO III-sensitive sites increased with natural radiation exposure in subjects from high-level natural radiation areas (P = 0.02), but when stratified according to smoking, a significant increase was observed only in smokers (P = 0.01). To the best of our knowledge, this is the first study on basal and oxidative DNA damage in healthy adults of this population. However, our findings need more validation in a larger study population.
A population-based 1:3 age-matched case-control study was conducted during 2006-2009 to assess the role of high-level natural radiation (>1 mSv/year) on congenital mental retardation and cleft lip/palate in the southwest coastal area of Kerala. Dosimetry was carried out in the house where parents resided during conception and the subsequent two trimesters of pregnancy of the study subject. Conditional logistic regression did not suggest any statistically significant association of either mental retardation (n = 445) or cleft lip/palate (n = 116) with high-level natural radiation. The odds of mental retardation and cleft lip/palate among those exposed to high-level natural radiation relative to normal levels of natural background radiation (≤1 mSv/year) were 1.26 (95% CI: 0.91-1.73) and 0.56 (95% CI: 0.31-1.02), respectively, after controlling for gender and maternal age at birth of the study subject. The data did not suggest any dose-related trend in the risk of either mental retardation (P = 0.113) or cleft lip/palate (P = 0.908). Notwithstanding the use of a single dose estimate to reconstruct past radiation exposure and the complex etiology of congenital malformations, it may reasonably be concluded that the prevailing high-level natural radiation in the study area does not appear to increase the risk of either mental retardation or cleft lip/palate among offspring of parents staying in the area.
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