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Buckle Up and Get at Least 7 Hours of Sleep Before You Drive
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 bureaus for Cephalon, Resmed, and Respironics.
Synopsis: In a representative sample of Americans, about a third reported getting less than 7 hours of sleep on average, about half reported snoring, and nearly 5% reported falling asleep while driving in the past month.
Source: McKnight-Eily LR, et al. Unhealthy sleep-related behaviors 12 states, 2009. MMWR Morb Mortal Wkly Rep 2011;60:233-238.
To collect these data, the centers for disease control and prevention (CDC) added an optional sleep module to its annual Behavioral Risk Factor Surveillance System (BRFSS). BRFSS is a state-based, random-digit–dialed telephone survey of the U.S. adult population. This survey has been conducted by state health departments in collaboration with CDC for many years. Some components are compulsory and are included annually, and others may be voluntarily included by individual states if their health departments wish. In this survey, California, Georgia, Hawaii, Illinois, Kansas, Louisiana, Maryland, Minnesota, Nebraska, New York, Texas, and Wyoming included the optional sleep module. Response rates ranged from 40.0% in Maryland to 66.9% in Nebraska, and included 74,571 adults.
The questions about sleep (and instructions to the interviewer) were: "On average, how many hours of sleep do you get in a 24-hour period? Think about the time you actually spend sleeping or napping, not just the amount of sleep you think you should get (categorized as < 7 hours and ≥ 7 hours)." "Do you snore? (can have been told by spouse or someone else; categorized as yes or no)?" "During the past 30 days, for about how many days did you find yourself unintentionally falling asleep during the day (categorized as none or at least 1 day reported)?" and "During the past 30 days, have you ever nodded off or fallen asleep, even just for a brief moment, while driving (categorized as yes or no)?"
About a third of the respondents (35.3%) reported sleeping less than 7 hours on average during a 24-hour period. The highest rate of this behavior was in Hawaii (44.6%), and the lowest was in Minnesota (27.6%). People who were at least 65 years old were significantly less likely to report sleeping less than 7 hours (24.5%) than persons in any other age categories. Non-Hispanic blacks (48.3%) and non-Hispanic persons of other races (38.7%) were more likely to report sleeping less than 7 hours than non-Hispanic whites (34.9%). There were no differences in self-reported sleep duration between men and women. Non-working adults, those with at least some college education, and single people were significantly more likely to report getting less than 7 hours of sleep.
Snoring was reported by nearly half (48%) of respondents, and its prevalence generally increased with aging. Men (57%) were more likely to report snoring than women (40%). And this survey demonstrates one of the problems with the epidemiologic estimation of snoring prevalence. Those who were married/partnered were more likely to report snoring than those who presumably slept alone, which is sort of like saying that if a tree falls in the forest and there's no one there to hear it, it doesn't make a sound.
About 38% of adults reported unintentionally falling asleep during the day at least once in the preceding month. This behavior was most likely in those between 18–24 years and those over 65 years. Again, there were no differences between men and women in the frequency of this behavior. Those who were unemployed, unable to work, or homemakers/students were significantly more likely to report unintentionally falling asleep during the day, but those with at least some college education were less likely to report unintentionally falling asleep than those with less education. Never married adults (43%) were significantly more likely to report unintentionally falling asleep during the day than married adults (36%). Those who reported getting less than 7 hours a night were more likely to report accidentally falling asleep during the day at least once in the previous month.
Nearly 5% of the respondents reported falling asleep while driving in the month before the survey. People who were 65 years or older (2%) were much less likely to report this behavior than persons aged 25–34 years (7%). Hispanics, non-Hispanic blacks, and non-Hispanics of other races all were significantly more likely to report this behavior than non-Hispanic whites. Men were more likely (5.8%) to say they had fallen asleep while driving compared to women (3.5%). No significant differences were observed by educational level or marital status. Those who reported getting less than 7 hours a night were more than twice as likely (7.3 vs. 3.0%) to report falling asleep while driving in the previous month.
Sleepiness is a problem when it interferes with daily activities. Falling asleep while driving is not just a personal problem, but a public health problem, since it endangers people besides the driver. In that regard, it's useful to look at this report with an eye to the factors associated with falling asleep while driving. Some are preventable, and some are not. Male gender, non-white race, and youth are the immutable factors associated with drowsy driving in this report. Being employed and sleeping less than 7 hours a night were potentially reversible factors associated with falling asleep while driving. These kinds of findings are tricky; for example, it is possible (likely, even) that those who work do more driving than those who don't. And the survey did not include questions about shift work, an important risk factor for crash. I am not suggesting that people should quit their jobs and get more sleep. But I do think that we need to query those who report drowsy driving about their sleep, and point out that sleep duration predicts sleepiness and drowsy driving (not just in this report, but in many others).1,2 So, take home message No. 1 is that people who report drowsy driving should be asked how much sleep they get at night. And remember, 7 hours is sort of a minimum. Some of us need more.
This report also includes estimates of snoring prevalence. Nearly HALF of Americans snore! As expected, snoring is more likely in men and in older people. I wish the investigators had investigated the relationship between snoring and some other data available on the BRFSS, such as Body Mass Index, drowsy driving, alcohol intake, and smoking status, all of which are likely to be correlated with snoring.3
But a caveat is in order. In this population, more people reported getting 7 hours of sleep a night than any other category (e.g., 6 or 8 hours ). And there are many, many studies demonstrating a U-shaped relationship between sleep duration and a gamut of outcomes including cardiovascular disease, obesity, and death.4-7 In most of these studies, the best outcomes are for those who report sleeping 7 or 8 hours a night. Sleep may be like calories: we need enough (which is variable among individuals, but probably about 7 or 8 hours), but too much is also associated with bad outcomes.
1. Pack AI, et al. Impaired performance in commercial drivers: Role of sleep apnea and short sleep duration. Am J Respir Crit Care Med 2006;174:446-454.
2. Scott LD, et al. The relationship between nurse work schedules, sleep duration, and drowsy driving. Sleep 2007;30:1801-1807.
3. Ulualp SO. Snoring and obstructive sleep apnea. Med Clin North Am 2010;94:1047-1055.
4. Cappuccio FP, et al. Sleep duration and all-cause mortality: A systematic review and meta-analysis of prospective studies. Sleep 2010;33:585-592.
5. Mesas AE, et al. The association between habitual sleep duration and sleep quality in older adults according to health status. Age Ageing 2011 Feb 17. [Epub ahead of print].
6. Kronholm E, et al. Self-reported sleep duration, all-cause mortality, cardiovascular mortality and morbidity in Finland. Sleep Med 2011 Feb 11. [Epub ahead of print].
7. Sabanayagam C, Shankar A. Sleep duration and cardiovascular disease: Results from the National Health Interview Survey. Sleep 2010;33:1037-1042.