American Journal of Epidemiology Advance Access originally published online on June 1, 2006
American Journal of Epidemiology 2006 164(1):19-20; doi:10.1093/aje/kwj201
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Response to Invited Commentary |
Lauderdale et al. Respond to "How Much Do We Really Sleep?"
1 Department of Health Studies, University of Chicago, Chicago, IL
2 Section of Endocrinology, Department of Medicine, University of Chicago, Chicago, IL
3 Department of Preventive Medicine, Northwestern University, Chicago, IL
4 Department of Health Economics and Management, Guanghua School of Management, Peking University, Beijing, China
5 Department of Epidemiology and Biostatistics, University of California at San Francisco, San Francisco, CA
6 Division of Research, Kaiser Permanente Northern California, Oakland, CA
Correspondence to Dr. Diane S. Lauderdale, Department of Health Studies, University of Chicago, 5841 South Maryland Avenue MC 2007, Chicago, IL 60637 (e-mail: Lauderdale{at}uchicago.edu).
Received for publication March 20, 2006. Accepted for publication April 14, 2006.
We enjoyed reading Stuart Quan's wide-ranging and poetic perspective on the importance of sleep, and we thank him for his insightful commentary (1
) on our paper (2). Noting the unexpectedly low average sleep duration in our study, he touched upon two possible sources of bias; both are intriguing suggestions. The first is that actigraphy might underestimate sleep compared with other measurement modes, and the second is that this cohort, based in Chicago, Illinois, is atypically sleep deprived.
Validation studies have concurrently measured sleep with polysomnography and actigraphy in a sleep laboratory setting, where polysomnography was the "gold standard" (3–6). These studies found no evidence that actigraphs consistently over- or underestimate sleep duration and latency in healthy subjects. However, we can speculate that there might be a fundamental problem with such validation studies if people sleep differently when attached to multiple sensors during polysomnographic monitoring, perhaps moving less than they normally do during sleep. Were that the case, then actigraphy in the home—where sleepers may be more active—might systematically underestimate sleep compared with actigraphy in the monitored sleep laboratory subject. There is no obvious way to prove or disprove this possibility.
We also agree that persons in northern metropolitan areas might sleep less than other persons. However, there are a great many people in such settings. The participants in the Chicago center of the Coronary Artery Risk Development in Young Adults study all lived in the Chicago area when the cohort started 20 years ago, but many have since moved and remain in the study. About 30 percent of the sleep study participants no longer live in the Chicago area. Nonetheless, participants may be more urban than the general population. Perhaps the urban setting is particularly salient for the Black study participants.
We want to reiterate that the average sleep duration we found for the White participants in our study is not inconsistent with the range of sleep durations reported in a number of prior small studies and case series. Rather, it is the average sleep duration of the Black participants that is surprisingly low, and prior studies have not included a sufficient number of Black participants for separate analyses.
We agree that these data, representing a single observational cohort, should not be considered normative. For normative data, adding wrist actigraphy to one cycle of the National Health and Nutrition Examination Study would be ideal. We are excited about the growing epidemiologic interest in sleep, and we look forward to comparing our data with those from other study populations as well as learning whether the sleep characteristics we measured influence the development of cardiovascular risk and other health outcomes among participants at the Chicago site of the Coronary Artery Risk Development in Young Adults study.
You're too fired up to go to sleep, you sit at the kitchen table. It's really late, it's really quiet, you're tired. Don't wanna go to bed, though. Going to bed means this was the day. This Feb 12th, this August 3rd, this November 20th is over and you're tired and you made some money but it didn't happen, nothing happened, You got through it and a whole day of your life is over. And all it is – is time to go to bed.Claudia Shear (1962–), playwright, Blown Sideways through Life (New York, NY: Samuel French, Inc., 2002, p. 12)
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ACKNOWLEDGMENTS |
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Conflict of interest: none declared.
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References |
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 TOP References |
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- Quan SF. Invited commentary: How much do we really sleep? Am J Epidemiol 2006;164:17–18.
[Free Full Text] - Lauderdale DS, Knutson K, Yan LL, et al. Objectively measured sleep characteristics among early-middle-aged adults: the CARDIA Study. Am J Epidemiol 2006;164:5–16.
[Abstract/Free Full Text] - Ancoli-Israel S, Cole R, Alessi C, et al. The role of actigraphy in the study of sleep and circadian rhythms. Sleep 2003;26:342–92.[Web of Science][Medline]
- Sadeh A, Sharkey KM, Carskadon MA. Activity-based sleep-wake identification: an empirical test of methodological issues. Sleep 1994;17:201–7.[Web of Science][Medline]
- Lichstein KL, Stone KC, Donaldson J, et al. Actigraphy validation with insomnia. Sleep 2006;29:232–9.[Medline]
- Jean-Louis G, von Gizycki H, Zizi F, et al. The actigraph data analysis software: I. A novel approach to scoring and interpreting sleep-wake activity. Percept Mot Skills 1997;85:207–16.[Web of Science][Medline]
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Related articles in Am. J. Epidemiol.:
- Objectively Measured Sleep Characteristics among Early-Middle-Aged Adults: The CARDIA Study
- Diane S. Lauderdale, Kristen L. Knutson, Lijing L. Yan, Paul J. Rathouz, Stephen B. Hulley, Steve Sidney, and Kiang Liu
Am. J. Epidemiol. 2006 164: 5-16.[Abstract] [FREE Full Text]
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