Questioning the Linear No-Threshold Model (LNT): Lessons From Hiroshima/Nagasaki and Fukushima

Abstract

Living organisms have been exposed to ionizing radiation throughout Earth’s 4-billion-year history, with humans presently receiving about 2 mSv of ionizing radiation every year. While radiation generates reactive oxygen and nitrogen species (ROS and RNS), organisms have evolved mechanisms to neutralize these toxic molecules and utilize them as signal transducers. High doses of radiation are harmful, but low doses are seemingly essential, and moderate doses can provide benefits—a phenomenon known as hormesis. Radiation exposure is currently regulated by the linear no-threshold model (LNT), which assumes all radiation is harmful, even at the smallest doses. However, substantial evidence, including insights into biological defense mechanisms like DNA repair, apoptosis, and immune system, supports hormesis. Although the Life Span Study (LSS) data historically backed the LNT, closer analysis reveals that low-dose radiation is linked to increased life expectancy and reduced cancer risk, invalidating LNT. During the 2011 Fukushima nuclear disaster, the Japanese government, adhering to the LNT-based precautionary principle, evacuated residents despite low contamination levels. This decision caused over 2000 deaths, though no fatalities were directly attributed to radiation. These findings challenge the LNT model and highlight the need for regulatory standards that incorporate thresholds and/or hormesis principles, better reflecting biological evidence.