Mortality and Comorbidity of Insomnia
First created | 05/12/2009
Last edited |
- Ohayon MM Mortality and Comorbidity of Insomnia, Sleep-EVAL Website, 2011
Insomnia is one of the most prevalent sleep disorders with nearly one third of the population having at least mild forms of insomnia (1).
Even when using the most restrictive diagnostic definition, there is still about 6% of the population who has insomnia. Asking if insomnia kills is certainly a legitimate question. The paper by Philips and Mannino is an elegant attempt to answer that question in a large community sample. Using a 6.3-year follow-up, the authors demonstrated that insomnia complaints and use of hypnotic medication were not associated with an increased mortality after controlling for other key variables. This is an important finding. However, the answer to that question is complex.
The publication by Kripke and his colleagues in 1979 (2) showing that short (less than 4 hours) and long sleep (10 hours or more) were associated with increased mortality, was a wake up call to the scientific community regarding to mortality risks associated with insufficient or excessive sleep.
Unfortunately, research in this area is still insufficient: about a dozen of scientific articles have addressed this issue with inconsistent results:
- Increased risk ratios for mortality were found in subjects who reported insomnia or
- abnormal sleep patterns (2-5) or
- use of sleeping pills (2,3,6,7), while other studies did not find insomnia to be related to increased mortality (7-10).
Several aspects need to be clarified before any definite conclusion can be reached.
THE FIRST DIFFICULTY TO OVERCOME IS HOW TO DEFINE INSOMNIA IN THE GENERAL POPULATION.
As previously underlined (1,11), a large definition will include many individuals with dubious insomnia and will prevent to reach reliable conclusion.
Insomnia encompasses more than the mere presence of sleep onset or sleep maintenance difficulties: it has a value only when it has a certain frequency, duration or recurrence and when it somehow impairs the functioning of an individual.
In the vast majority of the studies, the group of subjects with insomnia is heterogeneous including mild to severe insomnia and transient to chronic insomnia posing the problem of large within-group variability. This limitation was observed in nearly all mortality studies. The problem is that insomnia mortality risk studies often derived from surveys that were designed for other investigational purposes. Consequently, the number of questions addressing sleep issues was most of the time limited to one to four questions on insomnia symptoms and, sometimes, sleep duration was also asked. The time frame (past month, past year, lifetime) and frequency were rarely delineated and the duration of insomnia absent.
THE SECOND DIFFICULTY IS TO ESTABLISH CAUSALITY BETWEEN INSOMNIA AND MORTALITY CAUSES.
Several risk factors frequently associated with insomnia are in some instances a cause for insomnia and in other cases they are a consequence. One example is poor health status: degradation in health may lead to insomnia as the appearance of insomnia may contribute to deteriorate health (12). Therefore, the question is how often insomnia has triggered or has preceded the condition that led to death. To date, this question remains unanswered. Furthermore, we know little about the role of insomnia in the development of several diseases. For example, cardiac disease, a leading cause for death, has been several times associated with insomnia. However, studies assessing the influence of insomnia on the appearance of cardiac disease had the same limitations than mortality studies (inadequate definition of insomnia and lack of control for confounding factors) (13).
THE THIRD DIFFICULTY IS IN SELECTING THE CONFOUNDING FACTORS TO INTRODUCE IN THE PREDICTIVE MODEL.
The selection should be based on several considerations:
- their significant association with the studied outcome or their biological relevance (for example, age and gender);
- their frequency in the sample and;
- their minimal collinearity with the other confounding variables (i.e., information redundancy).
A consequence in introducing collinear variables in a model is that the variables can nullify each other, mask significant associations and allow the emergence of spurious risks.
To date, the evidence linking (or not) insomnia with increased mortality risks remains inconclusive. It is imperative that future studies improve the assessment and definition of insomnia in order to identify different groups of subjects with insomnia such as transient and chronic insomnia and the severity of insomnia.
The evaluation of severity should include frequency of symptoms and impact on functioning. Longitudinal studies that have assessed insomnia on different occasions have the possibility to evaluate if subjects with persistent insomnia (i.e., present at least at two different assessments) have a higher mortality risk.
In the eyes of the population, the current scientific knowledge about insomnia and mortality risk may appear somehow baffling:
- on one hand, studies show that you may die younger if you have insomnia (but it is not sure) or if you do not sleep the magic number of 7 hours per night (2-5, 7-10).
- On the other hand, studies (2,3,7) also show that if you are taking sleeping pills you will die younger anyway!
IN FACT, IT IS IMPERATIVE TO CALM DOWN THIS SITUATION: INSOMNIA WILL NOT KILL YOU AND TREATING INSOMNIA WILL NOT KILL YOU EITHER.
However, that does not mean that insomnia is a trivial condition. There is strong scientific evidence that insomnia is detrimental to health and quality of life and that it can be the first symptom of a more severe condition such as a depression, anxiety or a decrease in the immune system functioning (14-17).
PERHAPS, ASKING IF INSOMNIA KILLS IS NOT THE REAL QUESTION.
Beside fatal familial insomnia there is little evidence of a direct link between insomnia and death: Individuals will die of conditions associated with insomnia.
Instead, it can be the indication that awareness campaigns do not reach the population as much as it should be or the way it should be.
- Ohayon MM. Epidemiology of insomnia: what we know and what we still need to learn. Sleep Med Rev 2002; 6:97-111.
- Kripke DF, Simons RN, Garfinkel L, Hammond EC. Short and long sleep and sleeping pills. Is increased mortality associated? Arch Gen Psychiatry. 1979;36:103-116.
- Kripke DF, Garfinkel L, Wingard DL, Klauber MR, Marler MR. Mortality associated with sleep duration and insomnia. Arch Gen Psychiatry. 2002;59:131-136.
- Mallon L, Broman JE, Hetta J. Sleep complaints predict coronary artery disease mortality in males: a 12-year follow-up study of a middle-aged Swedish population. J Intern Med. 2002;251:207-216.
- Dew MA, Hoch CC, Buysse DJ, Monk TH, Begley AE, Houck PR, Hall M, Kupfer DJ, Reynolds CF 3rd. Healthy older adults' sleep predicts all-cause mortality at 4 to 19 years of follow-up. Psychosom Med. 2003;65:63-73.
- Kripke DF, Klauber MR, Wingard DL, Fell RL, Assmus JD, Garfinkel L. Mortality hazard associated with prescription hypnotics. Biol Psychiatry. 1998;43:687-693.
- Rumble R, Morgan K. Hypnotics, sleep, and mortality in elderly people. J Am Geriatr Soc. 1992;40:787-791.
- Brabbins CJ, Dewey ME, Copeland RM, Davidson IA, McWilliam C, Saunders P, Sharma VK, Sullivan C. Insomnia in the elderly: prevalence, gender differences and relationships with morbidity and mortality. Int J Geriatr Psychiat 1993; 8: 473-480.
- Foley D, Monjan A, Brown S, Simonsick EM, Wallace R, Blazer D. Sleep complaints among elderly persons: an epidemiologic study of three communities. Sleep 1995; 18: 425-432.
- Althuis MD, Fredman L, Langenberg PW, Magaziner J. The relationship between insomnia and mortality among community-dwelling older women. J Am Geriatr Soc. 1998;46:1270-1273.
- Ohayon MM, Roth T. What are the Contributing factors for Insomnia in the General Population? J Psychosom Res 2001;51:745-755
- Foley DJ, Monjan A, Simonsick EM, Wallace RB, Blazer DG. Incidence and remission of insomnia among elderly adults: an epidemiologic study of 6,800 persons over three years. Sleep 1999;22 Suppl 2:S366-S372.
- Schwartz S, McDowell Anderson W, Cole SR, Cornoni-Huntley J, Hays JC, Blazer D. Insomnia and heart disease: a review of epidemiologic studies. J Psychosom Res 1999;47:313-333.
- Ford DE, Kamerow DB. Epidemiologic study of sleep disturbances and psychiatric disorders. An opportunity for prevention? JAMA, 1989; 262:1479-1484.
- Breslau N, Roth T, Rosenthal L, Andreski, P. Sleep disturbance and psychiatric disorders: a longitudinal epidemiological study of young adults. Biol Psychiatry 1996; 39:411-418.
- Roberts RE, Shema SJ, Kaplan GA, Strawbridge WJ. Sleep complaints and depression in an aging cohort: A prospective perspective. Am J Psychiatry 2000;157:81-88.
- Cover H, Irwin M. Immunity and depression: insomnia, retardation, and reduction of natural killer cell activity. J Behav Med. 1994;17:217-223.