Insomnia is most often co-morbid with medical or psychiatric illnesses, medication use, circadian rhythm changes, and other sleep disorders. Foley et al found that although 28 per cent of older adults reported chronic insomnia, only 7 per cent of the cases were in isolation of common co-morbid conditions. They concluded that ageing alone does not cause sleep disruption, but rather the conditions that often accompany ageing result in poor sleep.
This belief was supported by data from the National Sleep Foundation’s survey of older adults which found a positive relationship between the amount of sleep complaints and the medical conditions, such as cardiac disease, pulmonary disease, stroke and depression. Likewise, as the number of medical conditions increased, so did the likelihood of having sleep difficulties29. In a large epidemiological study of older adults, heart disease, diabetes mellitus, and respiratory disease measured at baseline were all associated with long-term persistence of insomnia measured at a 3 yr follow up assessment28. Medical conditions such as arthritis, diabetes, chronic pain and cancer have all been associated with difficulty sleeping.
Insomnia is also often co-morbid with psychiatric disorders. Indeed, sleep disturbance among depressed patients is extremely prominent and is also one of the nine diagnostic criteria for depression30. Research supports a bidirectional relationship between depression and insomnia, such that mood disturbance can result in disturbed sleep and insomnia can place one at risk for developing depression31. Oftentimes, people undergoing significant life stressors such as divorce or loss of a loved one, may experience depression resulting chronic insomnia. Similarly, Buysee & colleagues31, found that the presence of insomnia at baseline was predictive of developing depression 1 to 3 yr later. A study conducted among older adults found similar results32. Insomnia also is a common comorbidity for other psychiatric disorders. Ohayon & Roth33 found that 65 per cent of depressed patients, 61 per cent of patients with panic disorder and 44 per cent of those with generalized anxiety disorder complained of insomnia.