Insomnia and mortality

Chronic insomnia is a frequent problem, and several studies have attempted to link insomnia with medical problems, even death. However, it's not clear from these studies that the relationship is as stated. One methodology problem with these studies is the fact that most of them define insomnia based solely on the research subjects' description of their sleep quality. In other words, secondary causes of insomnia are not ruled out with objective testing like sleep studies. This abstract is about research done on subjects with chronic insomnia. I don't have access to the actual article, so my analysis of the study is limited. I can't tell from the abstract if the research subjects had secondary causes of insomnia ruled out with sleep studies.

Researchers used data from a community-based cohort and categorized subjects into having either persistent, chronic insomnia, only intermittent insomnia, or no insomnia. The researchers defined persistent based on the subjects' description of their sleep quality over a six year period. They then determined when the subject died for up to a 20 year period. The researchers also examined levels of a marker of inflammation called serum C-reactive protein (CRP). There were 1409 research subjects - 249 with intermittent insomnia and 128 with persistent insomnia. The results showed that the subjects with persistent insomnia were 58% more likely to die than those without insomnia. Those with intermittent insomnia were not more likely to die than those without insomnia. Of note, most of the deaths were cardiovascular. CRP levels were higher in those with persistent insomnia than in those with either intermittent or no insomnia. The authors noted that CRP levels were associated with increased mortality by themselves. However, adjustment for CRP levels did not notably change the association between persistent insomnia and mortality. Also, the results were adjusted for confounders such as age, sex, body mass index, smoking, physical activity, alcohol, and sedatives.