Do Naps Get a Bad Rap?
Abstract & Commentary
By Barbara A. Phillips, MD, MSPH, Professor of Medicine, University of Kentucky; Director, Sleep Disorders Center, Samaritan Hospital, Lexington. Dr. Phillips reports no financial relationship to this field of study.
Synopsis: Regular napping in healthy people is associated with reduced coronary mortality, especially for working men.
Source: Natasha A, et al. Siesta in healthy adults and coronary mortality in the general population. Arch Intern Med. 2007;167:296-301.
This report comes from a secondary analysis of the Greek cohort of the European Prospective Investigation into Cancer and Nutrition [EPIC] study. The report results from a 6-year follow-up of 23,681 individuals who had no history of coronary heart disease, stroke, or cancer at enrollment. The study team hypothesized that regular napping would reduce coronary mortality. The authors were able to control for multiple health, anthropometric, and lifestyle variables, including age, smoking status, years of education as a socioeconomic status indicator, employment status, body mass index, waist-hip ratio, level of physical activity, and diet. Napping was categorized as:
1. never;
2. systematically (midday naps regularly, at least 3 times per week, with average nap duration of at least 30 minutes); and
3. occasionally (either once or twice per week [frequently on weekends] or short midday naps with average duration of less than 30 minutes, irrespective of the weekly frequency).
Mortality ratios for relevant variables did indeed show the expected positive relationships between age, smoking, central obesity and coronary mortality, as well as the expected inverse relationships between education, physical activity and adherence to the Mediterranean diet and coronary mortality. Most of the associations appeared stronger for women than for men, except that employment status was the strongest predictor of coronary mortality in men, with a two-fold increase in cardiac deaths in unemployed men, even after controlling for all other variables. Employment status was not associated with mortality in women. Compared with those who never napped, those who napped occasionally had a 12% lower rate of coronary death (mortality ratio 0.88, 0.48-1.60), and those who napped systematically had a 37% lower coronary death rate (mortality ratio 0.63, 0.42 0.93). When the authors separated the male part of the cohort into employed and unemployed men (there were not enough women working outside the home for meaningful analysis), they found that the benefit of napping was much greater for working men than for non-working men (mortality ratio 0.36 for working, CI 0.16-0.77, mortality ratio 0.64 for non working CI 0.33-1.21). Although the unemployed men were older, this relationship was not changed after adjusting for age.
Commentary
Napping is a hot topic! The prevalence of napping increases with age, and more than half of those over the age of 65 years in this country nap regularly.1 Several population-based studies in countries where the siesta is culturally ingrained have examined the relationship between napping and mortality.2-6 These studies have mostly indicated a positive association between napping and mortality However, small, well-controlled studies have suggested that planned naps can improve mood, alertness and blood pressure.7-9 The big question has always been: does napping kill, or is napping simply a marker of an underlying illness which is the real culprit? In addition, most studies of napping have not been able to carefully control for physical activity, which tends to be both cardioprotective and also to be associated with a reduced likelihood of napping.
My reading of this paper and the authors' careful analysis is that this report trumps the previous work on this topic. It is likely that employment status (especially for men), is a very important variable that affects both propensity to nap and mortality, and this will need to be rigorously controlled in future studies. Now we need studies of the effects of napping in cultures where women are more likely to be employed and where napping is less common than in the Mediterranean. From the present study, it is not possible to draw many conclusions about differences in coronary mortality rates between employed and unemployed women, since very few women in this Greek population were working outside the home. But the preliminary analysis suggests that the effects of being employed or unemployed are very different for men and women. For now, encouraging, rather than discouraging, regular napping seems like the way to go, especially in employed men.
References
1. National Sleep Foundation Sleep in America Poll, 2005.
2. Trichopoulos D, et al. Does a siesta protect from coronary heart disease? Lancet. 1987;2:269-270.
3. Kalandidi A, et al. A case control study of coronary heart disease in Athens, Greece. Int J Epidemiol. 1992;21:1074-1080.
4. Campos H, Siles X. Siesta and the risk of coronary heart disease: results from a population-based, case-control study in Costa Rica. Int J Epidemiol. 2000;29:429-437.
5. Bursztyn M, et al. Siesta in the elderly: risk factor for mortality. Arch Intern Med. 1999;159:1582-1586.
6. Hays JC, et al. Risk of napping: excessive daytime sleepiness and mortality in an older community population. J Am Geriatr Soc. 1996;44:693-698.
7. Monk TH, et al. Effects of afternoon "siesta" naps on sleep, alertness, performance, and circadian rhythms in the elderly. Sleep. 2001;24:680-687.
8. Tamaki M, et al. Effects of a daytime nap in the aged. Psychiatry Clin Neurosci. 1999;53:273-275.
9. Pelosio A, et al. Siesta, night sleep and blood pressure dropping. Blood Press Monit. 1997;2:27-30.
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