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Excessive Daytime Sleepiness in a General Population Sample: The Role of Sleep Apnea, Age, Obesity, Diabetes and Depression
Abstract & Commentary
By Barbara A. Phillips, MD, MSPH, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips serves on the speaker’s bureau of Cephalon, Boehringer Ingelheim, Merck, ResMed, and GlaxoSmithKline and is a consultant for Boehringer Ingelheim, Wyeth-Ayerst, and ResMed.
Synopsis: Complaints of sleepiness are common in those being treated for depression, in diabetics, in the obese, in smokers, and in those with sleep apnea.
Source: Bixler EO, et al. Excessive daytime sleepiness in a general population sample: the role of sleep apnea, age, obesity, diabetes, and depression. J Clin Endocrinol Metab. 2005;90:4510-4515.
This report comes from an analysis of data from the Penn State Cohort, which was assembled to investigate the age distribution of sleep apnea. A random sample of 16,583 people older than age 20 were interviewed by phone; a subset of 1741 of these individuals also underwent formal sleep testing (polysomnography) in a sleep center. The phone interview used a questionnaire that included basic demographic and self-reported health and sleep information. The presence of sleepiness was assessed by asking, "Do you feel drowsy or sleepy most of the day but manage to stay awake?" and "Do you have any irresistible sleep attacks during the day?" If respondents endorsed a moderate or severe rating on either of those questions, they were considered sleepy for purposes of this study. Depression was considered to be present if the subject was currently being treated for depression or endorsed suicidal thoughts or attempts. Diabetes was considered to be present if the participant had been diagnosed with diabetes by a physician, or in the subset who was studied in the sleep lab, or if fasting glucose was > 126. Sleep testing was done using standard techniques and definitions, and sleep apnea was considered to be present if the Apnea plus Hypopnea Index (AHI) was 15 or more events per hour of sleep.
The mean age of this cohort was 46.5 ± 0.1 years, and mean BMI was 26.3 ± 0.04 Kg/m2. In this population, 8.7% were sleepy, 13.0% diabetic, 13.3% depressed, and 4.4 % had sleep apnea. Men and women were equally sleepy in this cohort. There was a decline in reported sleepiness between the ages of 30 and 75 years, with increased sleepiness for those younger than 30 and older than 75 years. There was a marked increase in the prevalence of sleepiness for those with BMIs above 28 Kg/m2. There were also strong associations between reported sleepiness and both diabetes and treatment for depression.
In the subset of those randomly chosen 1741 participants who had sleep studies, those who reported sleepiness were no more likely to have low sleep efficiency (time spent sleeping divided by total time in bed) than those who did not. There were no differences in the sleep structure or quality of sleep between the sleepy and nonsleepy groups except for more awakenings for the sleepy group. Also, 18.3% of those with sleep apnea were sleepy, and 10.7% of those without sleep apnea were sleepy. This difference was statistically significant.
There was no association between reported sleepiness and the use of medications used to treat allergies, hypertension, thyroid disease, or "cardiac conditions," but those who used antidepressants were much more likely to report sleepiness. Bixler et al state that the relationship between sleepiness and depression did not change when they statistically controlled for the use of antidepressants, and they assert, "This supports the role of depression as a major risk factor for EDS in the general population."
After multivariate analysis, being treated for depression emerged as the most important risk factor for reporting sleepiness, followed by BMI, age (older people are less sleepy, at least up until the age of 75), self-reported sleep duration, diabetes, smoking, and finally sleep apnea.
This study interested me because it addresses an issue I have to consider nearly every day: the sleepy patient who doesn’t have sleep apnea. What else could it be? While sleep specialists talk a lot about narcolepsy and other arcane disorders, we know they are uncommon. In this study, depression (which is common) emerges as a powerful influence on sleep. We already know that depression is the single most important factor for insomnia,1 but the current paper suggests that depression and its treatment are also risk factors for sleepiness. Lifestyle, of course, also emerged as important, with both obesity and cigarette smoking conferring greater risk of sleepiness than sleep apnea. A large body of literature1,2 indicates that chronic illness is a risk factor for insomnia, which is often vaguely defined. In line with that literature, this study implicates diabetes as a risk for sleepiness.
Sometimes I worry that I haven’t gone far enough to evaluate patients who are referred for sleepiness if their sleep studies are negative for sleep apnea. This paper is reassuring to the clinician, and somewhat demystifies sleepiness, demonstrating that the "usual suspects" of depression, obesity, smoking, and diabetes are important underlying causes. Sleep apnea is prevalent and deadly, and it is important to rule it out, since CPAP treatment is highly effective. But if a sleep study is negative for sleep apnea? This paper suggests that many sleepy folks with negative sleep studies could benefit from those things that we do every day: counseling about weight loss and smoking cessation, considering depression or metabolic illness, evaluation of medications, and reassurance.
2. Foley D, et al. Sleep disturbances and chronic disease in older adults: results of the 2003 National Sleep Foundation Sleep in America Survey. J Psychosom Res. 2004;56:497-502.