International Journal of Epidemiology 2001;30:183
© International Epidemiological Association 2001
Letter to the Editor |
Author's Response
Cheng correctly points out that the afternoon nap is commonly practised in China, and in other countries with low coronary heart disease (CHD). In Greece, where the siesta practice was associated with lower risk of CHD, most of the population was involved in manual labour.1,2 However, one must not forget that only a small proportion of the Chinese and Greek populations are overweight and sedentary compared to ‘Westernized’ societies.1–3 Our study shows that taking daily siestas may be associated with increased risk of myocardial infarction (MI).4 In contrast to China, sedentary behaviour and obesity are very common in the Costa Rican subjects in the study. Our findings are supported by those in an elderly population where higher mortality rates were found among those that take naps.5,6 Furthermore, in NHANES I, those who reported that they ‘often’ or ‘almost always’ took a nap were at increased risk of stroke and CHD, and were more likely to be diabetic, overweight, hypertensive, and hypercholesterolaemic.7 A common thread that can tie together these apparently divergent findings is that siesta could be innocuous or even beneficial in people with high levels of physical activity and who are not obese, diabetic, hypertensive, or otherwise predisposed to CHD. This, of course, remains to be proven, since there are very few studies on this topic. In contrast, it is becoming quite clear that siesta, or napping, is not a particularly auspicious behaviour in societies with high morality rates from CHD, and high levels of risk factors. In these societies, a siesta may simply be a symptom of sedentary behaviour, and contribute to the worsening of obesity and its related risk factors, hypertension, diabetes, and hyperlipidaemia. We think that in ‘Westernized’ cultures, taking a walk may be more beneficial than an afternoon nap.
Cheng also points out in his letter that the afternoon nap is a stress-coping mechanism that can provide protection against CHD. However attractive an hypothesis this may be, we note that it is supported only by a letter of opinion, not scientific research. It may actually be of interest to test this hypothesis in a country such as China, particularly comparing the effects of napping within the rural versus the urban areas.
As a final comment we would like to clarify a misconception of Dr Cheng. Our study results are based on a population-based case-control study design. The cases were recruited within a week of their first MI and the questions asked referred to the year prior to their MI. Each case was compared to a control subject with no clinical disease, after matching for age, sex and area of residence.
Notes
Harvard School of Public Health, Boston, MA, USA.
References
1 Trichopoulos D, Tzonou A. Siesta and risk of coronary heart disease. Stress Med 1988;4:143–48.
2
Kalandidi A, Tzonou A, Toupadaki N et al. A case-control study of coronary heart disease in Athens, Greece. Int J Epidemiol 1992;21:1074–78.
3
Hu FB, Wang B, Chen C, Jin Y, Stampfer MJ, Xu X. Body mass index and risk factors in a rural Chinese population. Am J Epidemiol 2000; 151:88–97.
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;29:429–37.
5
Bursztyn M, Ginsberg G, Hammerman-Rozenberg R, Stessman J. The siesta in the elderly. Risk factor for mortality? Arch Intern Med 1999;159:1582–86.
6 Hays JC, Blazer DR, Foley DJ. Risk of napping: excessive daytime sleepiness and mortality in an older community population. J Am Geriatr Soc 1996;94:696–98.
7 Qureshi AI, Giles WH, Croft JB, Bliwise DL. Habitual sleep patterns and risk for stroke and coronary heart disease: 1 10-year follow-up from NHANES I. Neurology 1997;48:904–11.[Abstract]
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