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12-05-2013 | Sleep medicine | Article

Great East Japan Earthquake increases insomnia prevalence


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medwireNews: The prevalence of insomnia increased significantly among residents of Tokyo and Osaka following the Great East Japan Earthquake in March 2011, findings from a prospective study show.

The findings indicate the wide-reaching effects of such a disaster, given that the areas were relatively far from the epicenter, at 375 km for Tokyo and 750 km for Osaka.

The average daily prevalence of insomnia increased following the earthquake in both adults and minors (<20 years of age) from Tokyo, where the intensity of the tremors experienced was a Shindo Number of 5-Lower, out of a possible 7, on the Japan Meteorological Agency scale.

Hiroaki Sugiura (Nara Medical University School of Medicine, Kashihara, Japan) and colleagues say that this is likely to be "a direct result of the earthquake and its aftershocks."

By contrast, the average daily prevalence of insomnia increased in adults from Osaka, but not in minors. The intensity of tremors was lower in Osaka, at a Shindo Number of 3, and the researchers therefore suggest that the increased prevalence of insomnia in these adults may be a result of "mental stress induced by information broadcast by the media."

The 5053 study participants completed an online questionnaire daily for a period of 101 days between January and April 2011. Among the participants, 3128 were from Tokyo (2073 adults aged ≥20 years and 1055 minors) and 1925 from Osaka (1182 adults and 743 minors).

The average daily prevalence of insomnia among adults in Tokyo increased from 1.05% before the earthquake to 2.35% afterward, with an increase from 0.53% to 1.90% for minors. An increase from 1.25% to 1.83% was seen for adults from Osaka, whereas the prevalence remained largely the same for minors, at 0.092% before the earthquake and 0.089% afterward.

After taking into account age and region, the odds for insomnia were 1.2 times greater after the earthquake than before for participants from Tokyo, and 1.6 times greater for those from Osaka. The odds ratio for the two regions combined was 1.8.

"These results demonstrate an increased prevalence of insomnia among residents in regions located at considerable distances from the immediate zone of the disaster," Sugiura et al write in the Interactive Journal of Medical Research.

They conclude: "Health care practitioners should be aware that individuals might experience mental stress, including insomnia, even in areas distant from those that are directly affected by a natural disaster."

medwireNews ( is an independent clinical news service provided by Springer Healthcare Limited. © Springer Healthcare Ltd; 2013

By Lucy Piper, Senior medwireNews Reporter