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More than 5,000 passengers on Tokyo subway trains were injured with toxic chemicals including the nerve gas "sarin" on March 20, 1995. The purpose of this study was to identify the effect of sarin exposure on insomnia in a cross-sectional study. A self-administered questionnaire concerning sleep-related items was distributed to victims of sarin exposure in October and November, 2003. Questionnaires were completed by 161 of the 163 participants (98.8%), who were selected from 1,500 subjects. Among them, the authors selected 75 women 30 to 69 years of age. Control participants were collected from inhabitants living in Maebachi City, Gunma Prefecture, Japan. For the younger exposed group (under 50 yr. of age), percentages of poor sleep, difficulty falling asleep, intermittent awakening, early morning awakening, a feeling of light overnight sleep, and insomnia were significantly higher than those for the control group. In contrast, the older exposed group (ages 50 to 69 years) had significantly higher prevalence of poor sleep, a feeling of light overnight sleep, and early morning awakening for the exposed group when compared with the control group. The high prevalence of insomnia and insomnia-related factors for victims especially under 50 years of age suggests a need for research on sleep quality after sarin exposure. Although posttraumatic stress disorder is assumed to be a psychological effect of exposure to a toxic substance, a cause-and-effect relationship has not been established.

We previously reported that the frequency of sister chromatid exchanges (SCEs) among victims of the Tokyo subway sarin disaster was significantly higher than that of controls 2-3 months after the disaster. It has been reported that the victims were also exposed to the by-products generated during sarin synthesis, i.e., diisopropyl methylphosphonate (DIMP), diethyl methylphosphonate (DEMP) and N,N-diethylaniline (DEA) during the disaster and we previously found that DIMP, DEMP and DEA induced a significant SCE increase in human lymphocytes in vitro. To monitor the genetic aftereffects of the sarin exposure, SCEs of peripheral blood lymphocytes were measured in fire fighters and police officers involved in the disaster 3 years after the event. We found that the frequency of SCEs was still significantly higher in the exposed subjects than the controls, suggesting a risk of the genetic aftereffects of the sarin exposure. We further found a significant positive correlation between the frequency of SCEs and the inhibition of serum cholinesterase activity in the exposed subjects, suggesting that the elevated frequency of SCEs is related to the sarin exposure. On the other hand, there was no significant difference in natural killer activity between the exposed and the controls.