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Earlier surveys of sleep problems varied a lot in their techniques and findings. Few findings have turned up repeatedly. Estimates of the frequency of sleep problems in the general adult population have varied from 10% to 45%in different studies.
This study used a large sample of 14,800 male twins born between 1939 and 1955 and in military service between 1964 and 1975, obtained from the Vietnam Era Twin (VET) Registry.This VET Registry, created in 1987, had already obtained data on race at military induction and had subsequently mailed the participants a questionnaire survey of their health. Responders to this survey seemed to represent a relatively unbiassed sample of the whole group except that initial response rates were higher among white members (74%) than black members (57%). In 1990, a second mailed questionnaire surveyed (1) cardiovascular and pulmonary diseases and associated risk factors;(2) the Jenkins Sleep Questionnaire, comprising four questions about how often the month before a person had trouble falling asleep, trouble with waking up often during the night, trouble staying asleep, and trouble with waking up feeling tired; (3) illnesses diagnosed by a doctor; (4) height and weight; (5) smoking; (6) total alcohol consumption; (7) coffee and tea consumption; (7) marital status; (8) employment status; (9) social supports; (10) regular participation in church; (11) regular participation in club or community activity; (12) physical activity; and (13) components of the "Type A" behavior pattern associated with increased risk of heart disease.Qyestionnaires were mailed to 11,959 members and 8,870 responded (74%), again more often non-blacks (76%) than blacks (54%). Blacks made up 5% of the responding sample.
Excluding subjects with missing data, 8,438 subjects were available for analyses. Of these, 94% were employed, 76% were married, 36% were current smokers, 62% were current alcohol drinkers and 29% were heavy drinkers, 78% were current coffee drinkers and 12% were heavy coffee drinkers, 29% were tea drinkers, 86% engaged in light and 8% in strenuous physical activity. Their mean age was 40 (SD=3, range 33-51); their mean body mass index was 26 (SD=4, range 16-58).
With regard to the four specific sleep problems, 48% to 67% acknowledged having one or another of these at least once a month. Blacks acknowledged about one-third fewer sleep problems than whites on all items. Being employed was associated with reduced frequency of all sleep problems, as was participation in church and social support. Physical activity was associated with decreased sleep problems except for waking tired, which was increased, especially with strenuous activity. Heavier subjects reported more waking often during the night. Coffee consumption was related to trouble staying asleep; both coffee and tea consumption were related to waking tired. Heavy alcohol use was related to more of each type of sleep problem. However, current smoking was associated with less sleep problems. Higher education was related to less sleep problems except for waking often. The Type A personality was associated with increased risk of all sleep problems.
The most common medical condition in these subjects was high blood pressure, affecting 19%, and this was related to all sleep problems. So also were cardiovascular disease, chronic pulmonary disease, diabetes, migraines, ulcers, hemorrhoids, abdominal hernia, kidney stones, and rheumatoid arthritis. Only cancer and gallstones, among those illnesses present in at least 1% of the sample, showed no association with any sleep problems. However, the illness most powerfully related to increased sleep problems--doubling their risk--was depression.
The authors describe their results as representing "the first standardized data reported on non-white populations" although the focus of their analyses was not on race. The authors admit that specific values for prevalence of sleep problems are very susceptible to influence by demographics, specific questions asked, time interval of interest, and the sensitivity of the responses measured to the questions.
They noted that 83% of their sample reported at least one of the four sleep problems occurring at least once in the previous month, most often waking often (67%) and waking tired (62%), less often trouble falling asleep (48%) and trouble staying asleep (49%). They considered these figures comparable to another study of both sexes in Los Angeles where frequency of individual sleep problems ranged from 31% to 42%, but also mentioned a study of British men which found complaints in 19-22%, a study of Italian men of whom less than 30% complained of trouble falling asleep, and a study of Scottish men finding sleep complaints in 8-15%.
In this sample, a complaint of sleep problems seemed to represent a marker for many chronic conditions, especially those causing pain or affecting breathing. The authors commented that the sleep problems were more likely to represent an effect than a cause of these chronic conditions.
Analyses by twin pairs suggested that genetics were related to sleep problems, as indicated by heritability estimates of 0.21 to 0.42, though lower correlations among black twins suggested more importance for effects of shared environment rather than shared heredity.
The authors admitted the drawback of data limited to self-report through a mailed questionnaire, but asserted that this was the only practical approach for collecting data on thousands of individuals in an epidemiological study. They pointed out the relationships of sleep problems to many lifestyle variables that seem at least potentially modifiable--such as exercise, weight, alcohol, coffee, social involvement, employment, and Type A behavior--suggest ways of reducing these problems with sleep.
The authors' stress on the "multiracial" character of their sample seems puzzling until one realizes that this aspect may have representeda strong "selling point" in the process of gaining funding for the study. Their solitary race-related finding, that blacks complained of sleep problems less often than whites, could be called into question on the basis of self-selection bias, since the response rate among blacks was substantially lower than that among non-blacks. One suspects that a group with a long history of mistreatment by various "authorities" might be wary of admitting to medical or mental problems, especially when their inclusion in the study obviously derived from their prior involvement with an arm of the government. The questions asked may seem at first glance inoffensive enough to the reader, but many of them pull for responses that clearly indicate various types of incapacity, that is to say affirmative answers aren't "neutral" in terms of societal value judgmentswhether or not one has a job, goes to church, drinks, etc. I am suggesting that blacks, more than whites, would be disinclined to answer a questionnaire that would seem to show them in a bad light, and if they did answer would be less inclined to acknowledge problems, especially those often associated with "stigmatized" disorders as sleep disturbance is with depression.
Someone with sleep apnea may well wonder what this survey has to do with their own condition, since there is nothing very specific to sleep apnea in the questions asked. I could imagine that certain sleep symptoms, like waking up tired, would be more associated with sleep apnea than others, like difficulty falling asleep, but the association would be rather crude at best.One could wish the authors had included just a couple more questions, one about excessive daytime sleepiness and one about snoring, which would have extended the range of their findings to encompass what is probably the single most common understandable and treatable sleep disorder, sleep apnea. As it is, their major finding of a dominant relationship of sleep complaints to depression doesn't surprise me, since I think of depression as probably the most common cause of difficulties sleeping. Depression secondary to medical illness may also serve as an intervening variable to connect these chronic illnesses with sleep complaints.
Apart from its relationship to depression, insomnia doesn't have the same degree of specificity for diagnostic cause as excessive daytime sleepiness. It is especially nonspecific when it only occurs once a month, easily a result of situational stresses, and not representing a real disorder at all. I think of occasional insomnia as rather like occasional headache. If one asked men on the street whether they had a headache in the past month, I imagine one would get similarly high prevalences but know little about the seriousness of the symptom, which may range from a brief symptom easily relieved by aspirin to an incapacitating migraine attack. In fact, I would be surprised to meet someone who claimed never to have had a headache or a problem with their sleep; I would suspect them of denial!
Setting aside such criticisms of the study, I still find it interesting for several reasons. First, it demonstrates the enormous frequency of sleep complaints out of which we must do much weeding to get at the "real" sleep disorders which are of far lower frequency. Second, it gives us a glimpse of the web of interconnecting variables that relate to sleep difficulties. Many of these can be both cause and effect of sleep problems. For example, it is common knowledge that drinking too much caffeine, especially late in the day, can disturb sleep; but it may be much less well recognized that tired, sleepy people often turn to caffeine to keep themselves alert or at least functioning. Likewise, alcohol is thought to be disruptive of sleep(though this may not be as clearly demonstrated by data as one would suppose), yet probably serves as the most conveniently available and rapidly acting "sleeping potion" most people can obtain without a doctor's prescription.Physical activity, which "everyone knows" is good for your sleep, nevertheless was associated with waking up tired. Overweight, known to be a risk factor for sleep apnea, was associated only with complaints of waking often--which in fact might represent the respiratory-related arousals of that disorder. But overweight didn't show the universally harmful effects one might have expected, given its association with so many chronic medical illnesses, most of which affected sleep adversely in all ways.
To illustrate one "simple" variable that unfolds into endless complexity when one thinks carefully about it, take education. It seems that the more educated men slept better, except for waking often. Probably these men also had better incomes--though this was not measured--and as a result less financial stress, and easier access to medical services, including optimal treatment for their sleep disturbances and all related illnesses. Or could it be that their greater education (and possibly higher intelligence) led them to answer the questions in a different way, such as with less literal interpretation and more attention to the real-life significance of problems they reported? (As you may sense, it continues to astonish me that an individual who reports having difficulty sleeping one night in the past month could be viewed in any way as having a "sleeping problem," when the average moderately ill sleep apneic is aroused by respiratory events hundreds of times a night, every night of the month!)
I value this study not so much for what might seem to be its unusually high prevalence of reported "sleep disturbance" or even for its problematic (in the sense of being obscure) associations of these "disturbances" with various factors, as I do for the questions that it raises about our stereotyped understanding of what causes sleep problems. Depression we should all be aware of; even though its underlying pathophysiology is still mostly a matter of conjecture, it is nevertheless treatable. However, this fact may also serve to perpetuate the stigmatized stereotype of sleep difficulties as another "neurotic" symptom, when many of these difficulties are also strongly related to a myriad of chronic, quite physical diseases. The authors point to the various "lifestyle" factors which are related to sleep disturbance and might be modified to improve sleep, without apparently realizing that their findings can be used in quite an opposite manner--to "blame the victim" for his problems, because of the "bad habits" he has. In the context of numerous factors analyzed together, common wisdom about the invidious effects of alcohol, caffeine, and other "bad habits" on sleep take their rightful place as just a few among many contributors to sleep problems, which (at least, so I believe, are indeed multifactorial in origin.
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