Insomnia is often a symptom of depression, and depressed people often experience insomnia. But does one cause the other? Or do the two simply go together in no predictable way?
Researchers in the U.S. teamed up with Jules Angst and his colleagues in Zurich, Switzerland, to try to answer those questions. “We were able to look at insomnia alone, depression alone, and combined insomnia-depression,” says Daniel Buysse of the University of Pittsburgh School of Medicine, the lead author of the study. The research was reported in the April 1 issue of the journal Sleep.
Angst and Buysse’s team assessed psychiatric, physical and sleep symptoms in a sample of nearly 600 young Swiss adults at six interview times over 21 years. In 40 percent of subjects, insomnia that started mild around age 20 became chronic by age 40. “That’s important because it shows that insomnia tends to be a persistent problem, rather than just an occasional nuisance,” Buysse says.
As for the relationship between depression and insomnia, Buysse and Angst found that neither one clearly preceded or caused the other. However, insomnia (at one time) and insomnia coexisting with depression (at a later time) were strongly related. The number of subjects with insomnia who later experienced depression ranged from 17 percent to 50 percent at varying points in time.
“So it really looks as if insomniaplus-depression (the ‘combined’ state) is a ‘third state’ between insomnia and depression,” Buysse says. He believes the research raises the question of whether treatment of insomnia could reduce the risk of later developing depression. “Effective treatments for insomnia are available, and we can use them to help people feel and function better,” he says.