However, no in vivo data is available regarding telomere length in humans exposed to chronic low dose ionizing radiation. The high level natural radiation areas in the world provide such opportunities to study the effect of natural chronic low dose radiation.
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Confounding factors such as age, gender and other habits etc. Therefore, to delineate the effect of ionizing radiation, if any, on the telomere length of the studied individuals, it is necessary to do the dose response study. In general, a linear relationship would give an indication of radiation induced effects, if any. The telomere length was almost stabilized in later dose groups from high level natural radiation areas. This finding suggests that the natural chronic low background radiation dose did not have significant influence on telomere length.
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Assuming that the high level of background back ground radiation can induce increasing DNA damage with increasing background dose level, we could have expected significantly shorter telomeres in the higher dose groups and in a dose dependant manner. No clear-cut decrease in telomere length was observed, suggesting a better repair of telomeric ends in natural background area. Telomere attrition is known to be correlated with DNA damage response  leading to detection of significant DNA damage.
Micronuclei formation is one of the indicator of radiation induced DNA damage. This area is under investigation since many years. For micronuclei study, newborns were analysed in peripheral blood lymphocytes in this study area 61 samples from NLNRA and from HLNRA using cytochalasin blocked micronuclei assay. Over one million binucleated cells were scored. Similarly, dicentric formation is another indicator of radiation induced DNA double strand breaks.
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Between and , chromosomal aberrations were analysed in the peripheral blood lymphocytes PBLs of 14, newborns in the Kerala coastal belt whose mothers were exposed 1. The cytogenetic investigation included both stable and unstable aberrations.
A total of nearly 1 million metaphases were scored. No correlation was found between the background radiation dose and the frequency of chromosomal abnormalities. DNA repair study and transcriptome analysis on a statistically significant number of individuals are in progress in order to address some of these issues unpublished data.
There are reports, which suggest that telomere length in germinal cells is maintained where as, in somatic cells it decreases with age  , . In most of the somatic cells, telomerase activity is usually not found  ,  except few observations  , . The real time q-PCR methodology used in our study is an established method by Cawthon  ,  for measuring relative telomere length which is correlated with telomere length obtained from Southern blot analysis by many investigators.
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Recently there are studies, which have shown that the telomere length can be calculated in terms of base pairs from the relative telomere length . It is to be pointed out here that the telomere length detection by southern blotting covers the sub-telomeric region whereas the primers designed by Cawthon in  detect only the telomere specific repeat. Preliminary data from our laboratory on transcriptome analysis using affymetrics gene expression arrays human genome U plus 2.
All of these genes have shown a fold change of less than 1.
It also rules out methodological errors, if any. Measurement of telomere length by using real time PCR is an accepted method of choice from human blood samples as it requires small quantity of DNA. That is the reason this method may be useful for forensic invesigations  , . Telomere length and its association with aging have significant implications to human health .
Telomere length has been negatively correlated with aging and age related diseases  ,  , . In the present study, although our main objective was to study whether there is any difference in the telomere length due to the effect of chronic natural background radiation, we also looked at the telomere length with respect to age.
Several studies have reported that telomere length becomes shorter with the advancement of the age  ,  , . In other words, shorter telomere length is observed in older age groups as compared to younger age groups. Similar trend was found both in male and female individuals.
We have analysed our data to find out the difference of telomere length with respect to both the sex. There are many studies showing significant difference in telomere length among male and female adults. Many studies have shown that the telomere length in females is significantly longer than males  ,  ,  , .
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In the present study, we did not observe any significant differences in telomere length in male and female adults with respect to all the above five background dose groups as shown in figure 2. This finding is also similar to our cytogenetic findings in male and females newborns and the micronuclei frequency. The limitation of our study is that we need to collect more individuals from the older age group. Perhaps cumulative radiation dose might give a clear picture of telomere length among the adults from all the age groups.
Since the population is living in this area for at least 50 generations, the adult samples analysed in the present study have sufficient exposure to low dose natural radiation during their life. Although our limitation is we have studied adults of a younger age group, older population needs to be anlysed to have a clear-cut picture of the cumulative exposure effect in their life time. To our knowledge, this is the first in vivo study which attempts to address the dose response relationship between natural chronic background radiation and telomere length in human peripheral blood mononuclear cells.
The presence of large inter-individual variation in telomere length, telomere length attrition between males and females, telomere length loss during different stages of life, association of telomere length and age, genetic factors and environmental factors give rise to the large amount of variation of telomere lengths a population. Therefore, studies pertaining to telomere length regulation during the life span might provide a clearer picture of the association between telomere length and age.
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In the present investigation, venous blood samples were obtained from normal, healthy adults males and females with a mean maternal age of The study was approved by the institutional ethic committee of Bhabha Atomic Research Centre, Mumbai and all the participants gave written informed consent. The average radiation levels for the family are incorporated for each adult individual and the data entry is verified and validated for internal consistency.
The study area is a coastal belt of about 55 km long and 0. Hence area with an exposure above 1. The classification of high level and Normal level natural radiation is based on the level prevailing at the residence of the individual. Greiger Muller Counters were used for measuring the terrestrial gamma radiation and average area dose was calculated from 0.
Relative telomere length was determined by using the approach as previously described by Cawthon in  with a little modification in the PCR temperature conditions. This method measures the factor by which the ratio of telomere repeat copy number to single — gene copy number differs between a sample and that of a reference DNA sample.
PCR amplification was achieved using telomere T and single copy gene, 36B4 encodes acidic ribosomal phosphoprotein primers S which serves as a quantitative control. The expression of single copy gene 38B4 was validated using another positive control beta-globin gene. All the samples were run in triplicates in order to minimize the sample to sample variation. The same sample was also repeated in another day and run in triplicates.
The p values were the same in different experiements for the same sample or individual. The error value indicates the degree of well to well variation in the 96 well plate used for the PCR experiment. A standard curve derived from serially-diluted reference DNA was generated in order to check PCR efficiency between the plates. For quality control purposes, we have repeated many samples that were separately PCR amplified.
Majority of the samples were repeated more than twice and run in different plates in order to achieve the consistency. All the measurements were performed in a blinded fashion without knowledge of sample information.
Statistical analysis of the samples was performed using the statistical software Sigma stat 3. The relationship between telomere length and radiation dose, effect of gender and age were determined using least squares linear regression analysis. Odds ratio OR and their confidence intervals CI were calculated in order to see statistical significance in the mean of short and long telomere length among the adults from various dose groups as compared to control.
Using analysis of variance ANOVA , pairwise comparisons were performed in order to see the differences in the mean telomere length between the groups normal, and three dose groups from HLNRA. Regression analysis was performed to find out the correlation between telomere length and age.
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The authors wish to thank to the donors, who willingly donated the blood samples. We acknowledge with thanks all the staff members of Low Level Radiation Research Laboratory, Kollam and the Government Hospital units of Kerala for their co-operation during the blood sample collection. Sandstone is one: most sand grains are quartz some may be feldspar , which is usually pretty low in radioactivity. Limestone marble too is usually low in radioactivity, although the local rock in Ramsar is freshwater limestone that happens to have sky-high levels of radioactivity.
Having said that, Ramsar is an unusual place; as far as I know there's no other place where the limestone has this property. Okay, so let's put all of this together. First, there are some extreme examples—like the freshwater limestone in Ramsar or the black shales in Sweden—in which rocks can be radioactive enough to potentially give you a high dose of radiation. And in these locations, studies have been done and there's no indication that living in these dwellings is harmful. Second, there are some geologic materials real granites, for example that have more radioactivity than other types of rock.
But—and this is important—even granites don't give you a high enough radiation dose to be dangerous. I live in New York City, where we have a lot of granite buildings. I can measure the radiation from these buildings and there's no doubt that it's somewhat elevated, but the dose rates are still far too low to be a health risk. One final thing: even wood, brick, and concrete give off low levels of radiation—usually not much, but some. You won't be able to find any building materials that are totally bereft of radioactivity; it's just that some are more radioactive than others.
But unless your house is made of something with exceptionally high levels of radioactivity, you don't have to worry that it will affect your health.