Insomnia tied to depression risk in Japan

People who struggle to get a good night's sleep are twice as likely, on average, to suffer from depression down the road as those who sleep soundly, Japanese researchers report.

After surveying thousands of adults in a rural Japanese town over the course of two years, a team from Tokyo Medical University found that participants with insomnia at the study's outset were up to two and a half times more likely to have a new or ongoing case of depression by the end.

"The study is interesting because it confirms again that there is a connection between sleep abnormalities and depression," said Dr. Srinivasan Pillay, an assistant clinical professor of psychiatry at Harvard Medical School, who was not involved in the work.

"What it does not tell us," Pillay told Reuters Health, "is whether sleep abnormalities are the cause of depression or something else. It tells us there is an association between the two."

Because a growing body of research shows a link between insomnia and depression, researchers led by Dr. Yuichi Inoue in the Department of Somnology at Tokyo Medical University set out to see whether it held true over time in a Japanese population. They also looked at whether specific types of insomnia were especially tied to future depression risk.

It was already known that one-fifth of the Japanese population reportedly suffers from insomnia and that sleep problems were a suspected risk factor for other psychiatric disorders such as anxiety, depression and substance abuse. But little research had been done in Japan.

CHRONIC INSOMNIA AFFECTS APPROXIMATELY 9% TO 12% OF THE POPULATION 1-3 AND IS MORE PREVALENT THAN HEART DISEASE, CANCER, AIDS, neurologic disease, breathing problems, urinary problems, diabetes, and gastro- intestinal problems. 4 Researchers estimate the total annual cost of insomnia is $30 to $35 billion. 5 Although insomnia is highly prevalent, it is not commonly viewed as a significant threat to health. However, research has shown that a strong relationship exists between insomnia, depression, and anxiety, where insomnia may be a risk factor. 6 Unfortunately, the exact nature of this relationship remains unclear because previous studies have had varied definitions of insomnia and sometimes did not control for confounds. The current study defined insomnia using empirically validated criteria and controlled for possible confounds to obtain unbiased estimates of the relationship between insomnia, depression, and anxiety. We further elucidated this relationship by exam- ining depression and anxiety associations with insomnia severity and insomnia type.

Starting in 2005, Inoue's team administered two surveys to nearly 3,000 adults in the town of Daisen in Tottori Prefecture. One survey was designed to measure insomnia symptoms and the other to detect depression.

The insomnia survey let researchers analyze categories of sleep disturbance, including sleep quality, the amount of time participants took to get to sleep, sleep duration, sleep "efficiency" and daytime dysfunction.