NONLINEARITY OF RADIATION HEALTH-EFFECTS

The prime concern of radiation protection policy since 1959 has been t o protect DNA from damage. In 1994 the United Nations Scientific Commu nity on the Effects of Atomic Radiation focused on biosystem response to radiation with its report Adaptive Responses to Radiation of Cells and Organisms. The 1995 National Council on Radiation Protection and M easurements report Principles and Application of Collective Dose in Ra diation Protection states that because no human data provides direct s upport for the linear nonthreshold hypothesis (LNT), confidence in INT is based on the biophysical concept that the passage of a single char ged particle could cause damage to DNA that would result in cancer. Se veral statistically significant epidemiologic studies contradict the v alidity of this concept by showing risk decrements, i.e., hormesis, of cancer mortality and mortality from all causes in populations exposed to low-dose radiation. Unrepaired low-dose radiation damage to DNA is negligible compared to metabolic damage. The DNA damage-control biosy stem is physiologically operative on both metabolic and radiation dama ge and effected predominantly by free radicals. The DNA damage-control biosystem is suppressed by high dose and stimulated by low-dose radia tion. The hermetic effect of low-dose radiation may be explained by it s increase of biosystem efficiency. Improved DNA damage control reduce s persistent mis- or unrepaired DNA damage i.e., the number of mutatio ns that accumulate during a lifetime. This progressive accumulation of gene mutations in stem cells is associated with decreasing DNA damage control, aging, and malignancy. Recognition of the positive health ef fects produced by adaptive responses to low-dose radiation would resul t in a realistic assessment of the environmental risk of radiation.