Radiation, Science, and Health

"Low Level
Radiation Health Effects: Compiling  the Data"

Revision 2
March 30, 1999

by Radiation, Science, and
Health, Inc.,
Edited by J. Muckerheide

1.2 Human Population Epidemiology

References

"The increased use of nuclear technology has created fear in the minds of people regarding its possible adverse effects on living systems. This fear is heightened by press reports of nuclear fallouts and of high levels of natural background radiation in geographical areas in a number of countries. The International Commission on Radiological Protection and the United Nations Scientific Committee on the Effects of Atomic Radiation estimate the risk of cancer from high dose exposure to be 4.5% to 7.1% per sievert depending on the projection model used. However, when the exposure is to low dose background radiation, the available data does not show an increased risk. This is possibly due to the effectiveness of the inherent repair capacity of the living cell. These observations have given rise to the 'hormesis' hypothesis. Low dose radiation has in fact been found to be immuno-stimulatory and this is now being exploited as a possible treatment modality in cancer patients."

"…It was initially presumed that any level of radiation exposure is harmful. However, over the years, scientific data has accumulated to show that radiation effects follow a 'threshold response' and exposures only above this level are harmful. Recent observations have pointed to a 'hormesis' effect-the beneficial effect of a hazardous substance."

"Another cause for concern is the exposure to natural background radiation. Areas with high natural background radiation emanating from rocks and soils containing radioactive materials such as uranium, thorium and potassium-40 have been mapped in countries such as China, Brazil and India. In India, the coastal belt of Kerala has a high level of thorium (George et al 1976). The radiation dose in this area varies from 1.5 to 20 millisieverts (mSv) per year (Cheriyan et al 1992), the highest annual exposure being 278 mR/hour (0.0035 Sv/hour) outside a dwelling unit and 1215 mR/hour (0.012 Sv/hour) for an individual (Ramachandran et al 1994)."

"…The dose of radiation to which individuals residing in natural background areas are exposed is much lower than the dose at which adverse effects have been documented. Most workers believe that the effects of low dose radiation exposure are different from those due to a high dose. Thus, the effects of high dose exposure cannot be extrapolated to those of a low dose.

"Marshall (1993) supports the view that a given dose of radiation is less risky if received over an extended period of time. The lack of an increased incidence of cancer and hereditary diseases in the radiation 'hot spots' of the world further supports this (Nambi 1994, Liu 1992). Reports from these areas even suggest a stimulatory effect of low doses of radiation akin to the homeopathic principle that hazardous substances can be therapeutic when given at extremely low doses-the 'hormesis' effect (Luckey 1980, Sugahara et al 1992). A number of mechanisms have been described for this effect including enzyme activation, increased DNA repair and immune stimulation."

"Epidemiological studies reported so far in areas of high natural background radiation have pointed to a lack of increased incidence of cancers and related genetic disorders (Nambi 1994, Sugahara et al 1992, Rose 1982, Gillespie 1991, Sjernfeldt et al 1987, Nambi 1987, and Taylor 1992) indicating that people residing in these areas have either an enhanced resistance (inherent or acquired) to radiation damage or an increased capacity for DNA repair..."

"To summarize, the literature supports the view of an increased production of DNA repair enzymes, faster DNA repair and development of radio-resistance on exposure to low dose radiation. These effects are beneficial and could be the reason for the absence of an increased incidence of cancers in people residing in areas with natural background radiation."

"…Is the situation the same in long term residents of areas with high background radiation? Studies carried out by Japanese and Chinese scientists as well as by us suggest that none of the immunological variables such as lymphocyte transformation, NK cell activity, interferon levels, lymphokine augmentation of cytotoxicity and T lymphocytes are altered in residents of areas with high background radiation when compared to controls (Eguchi-Kasai et al 1991, Akiyama et al 1983, Pillai et al 1989a, Pillai et al 1989b, Balaram et al 1988, Pillai et al 1991, and Nair et al 1986)."

"…Preliminary data have shown a prolongation of survival in cancer patients when combination therapy with low dose X-rays and biological response modifiers was used (Uchida 1992). These findings suggest that low dose radiation often stimulates immune functions."

"Recent studies in areas where there is a high natural background radiation suggest that it may impart beneficial effects as evidenced by reports of an absence of increased incidence of cancers and other congenital diseases. A number of experimental studies support these observations….Takai et al (1992) demonstrated an enhancement of anti-tumour immune responses by total body irradiation with doses up to 1.5 Gy/10 fractions/4.5 weeks and suggest that this could be used in the treatment of diseases where there is immuno-suppression such as AIDS and non-Hodgkin's lymphoma.

"A study from our centre suggests that radiation exerts an antetardent effect on the growth of second primary tumours (Bhattathiri 1992). A number of reports are available wherein radiation causes the chromosomal aberrations which are associated with childhood leukaemia (Luckey 1980) but there are no data, however, to show that these manifest clinically. This is probably due to the increased capacity of DNA repair and increased immune stimulation. Thus exposure to very low doses of radiation should not cause great concern. Studies have been mounted in the radiation 'hot spots' in Kerala and the results so far support that a high level of natural background radiation is not hazardous. In fact it appears that low dose radiation increases the resistance of the body to higher doses. Scientists now suggest that a certain optimal background radiation is essential for survival."