PITTSBURGH-- Excessive daytime sleepiness--often a sign of sleep-disordered breathing--may represent an important risk factor for increased mortality in the elderly, particularly among women. A recent study found that daytime sleepiness was the only sleep disturbance symptom associated with both total and cardiovascular mortality.[1] Furthermore, daytime sleepiness appears to be an independent predictor of death and cardiovascular disease in women.

"If an older person is tired during the day, the quality of his or her nighttime sleep needs to be examined," said lead author Anne B. Newman, MD, MPH, an associate professor of medicine and epidemiology in the Division of Geriatric Medicine at the University of Pittsburgh School of Medicine.

Study participants included 5,888 men and women, age 65 years or older, who were recruited for the Cardiovascular Health Study (CHS). Sleep habits, including sleep patterns, were assessed by an interview-administered questionnaire. Respondents were asked about daytime sleepiness, difficulty falling asleep, frequent nighttime awakening, early morning awakening, and loud snoring.

Frequent awakening was the most common symptom in both men and women (Figure 1). Difficulty falling asleep was more common among women, whereas snoring was more common among men. The prevalence of daytime sleepiness and early morning awakening was similar in men and women. Overall, 17% of the CHS cohort reported daytime sleepiness.

Figure 1 Sleep Disturbance Symptoms in the Elderly

Data extracted from Newman AB et al. J Am Geriatr Soc. 2000.[1]

INCREASED RISK FOR WOMEN

Daytime sleepiness was the only sleep symptom that was significantly associated with increased mortality in both men and women. However, women with daytime sleepiness had almost double the risk of death than did other women, whereas for men daytime sleepiness increased the risk of death by only about 40%. "Part of this difference is that elderly men are already at higher risk for increased mortality," Dr. Newman said.

However, other variables may also account for the difference, she added. "The risk of [cardiovascular disease] is often underestimated in older women. It is possible that heart disease is unrecognized in women because [some] of its symptoms, such as poor sleep, may be less specific in women than in men."

The researchers also found daytime sleepiness to be an independent risk factor for total and cardiovascular mortality in women, but not in men. "In women, the risk of mortality appeared to be independent of their age and other health factors that we adjusted for," Dr. Newman noted. In contrast, "in men, the risk of mortality seemed to be more age-related."

Overall, the mortality rate (per 100 person-years) was:

• 3.86 in men without daytime sleepiness.
• 5.32 in men with daytime sleepiness.
• 1.69 in women without daytime sleepiness.
• 3.48 in women with daytime sleepiness.

Several other gender-specific differences were detected. For example, men who reported difficulty falling asleep had an increased mortality rate (hazard ratio, 1.43), which was not seen in women.

On the other hand, women reporting both daytime sleepiness and frequent awakening had a markedly higher risk of congestive heart failure (hazard ratio, 2.34) than did women who reported daytime sleepiness in the absence of frequent awakening. This increase in risk was not seen in men. The overall risk of morbidity and mortality from cardiovascular disease was significantly elevated in the women--but not the men--with daytime sleepiness.

SYMPTOMS OFTEN OVERLOOKED

Nighttime sleep disturbances often go unrecognized by patients and physicians or are considered to be "normal" in older adults.

Both sleep-disordered breathing and nocturnal myoclonus increase in frequency with age, Dr. Newman noted, yet they do not always cause full arousal, and thus patients may not realize why they are awakening at night. Nevertheless, research has demonstrated that sleep arousals and sleep-related respiratory disturbance are more common among the elderly.

Interestingly, the investigators found that snoring was inversely related to mortality and cardiovascular disease in men. They offered several possible explanations for this finding. For example, many older people are unaware of their snoring. "Another possible factor may be that many people with snoring problems don't survive to old age and are, therefore, underrepresented in this study," Dr. Newman suggested.

She added, "I think that there is a good chance that daytime sleepiness predicted mortality in our study because some of the people we studied have underlying breathing problems that are making their sleep inefficient at night and leaving them tired during the day, but they just don't know they have breathing problems."

UNDERLYING MECHANISMS

Despite the study's finding that nighttime sleep disturbances, especially snoring, were not associated directly with mortality or cardiovascular disease, the authors believe that sleep-disordered breathing may represent an underlying mechanism in the association of daytime sleepiness with cardiovascular disease and mortality. Further research, they suggested, might identify a subgroup of people with treatable conditions, such as sleep apnea or early congestive heart failure.

In an accompanying editorial,[2] Naresh M. Punjabi, MD, and Edward Haponik, MD, of the Division of Pulmonary and Critical Care Medicine at Johns Hopkins University proposed several theories to explain the relationship between excessive daytime sleepiness and cardiovascular morbidity and mortality. First, they suggested that excessive daytime sleepiness may stem from an underlying sleep disorder. In fact, the prevalence of sleep-disordered breathing in the elderly and its association with cardiovascular disease and mortality has been well documented, the authors pointed out.

"Second, many of the chronic medical conditions that are prevalent in older people, such as coronary heart disease, congestive heart failure, emphysema, and depression, can be related indirectly to [excessive daytime sleepiness] through their interference with nocturnal sleep quality," the authors noted. Although few of the subjects who reported daytime sleepiness in this study indicated having significant levels of physical impairment or clinical cardiovascular disease, previous research has reported an association between daytime sleepiness and poorer self-reported health.[3]

Finally, excessive daytime sleepiness may directly contribute to morbidity and mortality, albeit through an unidentified mechanism.

--Bob Kronemyer

References
1. Newman AB, Spiekerman CF, Enright P, et al, for the Cardiovascular Health Study Research Group. Daytime sleepiness predicts mortality and cardiovascular disease in older adults. J Am Geriatr Soc. 2000;48:115-123.
2. Punjabi NM, Haponik E. Ask about daytime sleepiness. J Am Geriatr Soc. 2000;48:228-229.
3. Newman AB, Enright PL, Manolio TA. Sleep disturbance, psychosocial correlates, and cardiovascular disease in 5201 older adults: the Cardiovascular Health Study. J Am Geriatr Soc. 1997;45:1-7.