Too little or too much sleep may increase mortality risk
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Sleeping less or more than 7 hours was significantly associated with an increased mortality risk in men and women, according to an East Asian study published in JAMA Network Open.
“The results of the current study thus suggest that 35% of East Asian men and 29% of East Asian women whose sleep durations of 8 hours are in accord with current sleep duration recommendations of the U.S. National Sleep Foundation may be at an increased risk of death from all causes and other causes (men and women) as well as CVD (women only),” Thomas Svensson, MD, PhD, a researcher in the Center for Public Health Sciences at the National Cancer Center in Tokyo, and colleagues wrote.
Svensson and colleagues conducted a cohort study of 322,721 individuals in Japan, China, Singapore and Korea; the mean age was 54.5 years; 55.3% of participants were women. Data on the participants’ health and sleep patterns were collected from Jan. 1, 1984, to Dec. 31, 2002. The mean follow-up was 14 years for men and 13.4 years for women.
The most common sleep duration was 8 hours for men (35.1%) and 7 hours for women (33.8%). Overall, 7 hours of sleep yielded the lowest associations with all-cause, CVD and other-cause mortality, according to the researchers. Ten hours of sleep or more had the greatest association with all-cause mortality in men (HR = 1.34; 95% CI, 1.26-1.44) and women (HR = 1.48; 95% CI, 1.36-1.61).
During the study period, 19,419 men and 13,768 women died. Svensson and colleagues found that sex was a significant modifier for the association between sleep duration and mortality from CVD (P = .02), cancer (P = .007) and other causes (P = .03). Additionally, age was a significant modifier for men (all-cause mortality, P < .001; cancer, P < .001; other-cause mortality, P < .001).
The association between CVD mortality and sleep was increased in men sleeping 5 hours or less and 9 hours or more and in women sleeping less or more than 6 hours, the researchers reported. The association between cancer mortality and sleep was increased in men sleeping 8 hours or more, while in women, it was present in those sleeping 10 hours or more. Lastly, the association between mortality from other causes and sleep was increased in men sleeping less or more than 6 hours and in women sleeping 8 hours or more.
“An important reason to conduct analyses specifically in Asian populations is the increased likelihood of short sleep among Asians and stronger associations of long sleep duration with mortality in this racial group compared with other populations,” Svensson and colleagues wrote.
Additional research is required to ascertain the mechanisms behind the associations between sleep duration and mortality, the researchers concluded.
Perspective
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Michael Grandner, MD
For over 50 years, population-based research has demonstrated that people who do not get the recommended 7 to 8 hours of sleep every night have shorter lives. There are likely a variety of causes for this, as sleep is linked to cardiometabolic, immunological, mental and cognitive health. In response to this research, various groups have advocated for age-appropriate sleep length guidelines. Standardized recommendations have enabled uniform guidance in clinical care delivery and group comparisons.
In this context, Svensson and colleagues investigated the links between sleep duration and mortality in four East Asian countries (Japan, China, Singapore and Korea). This work has some essential lessons for the researchers and the public at large.
First, this study confirms that habitual sleep length is an essential health risk factor, especially in groups that are normally understudied in this area. As such, it highlights the issue of sleep length as a global health concern, affecting people in a variety of countries and sociocultural circumstances. Second, this study emphasizes the need for practices and policies that address the diverse links between sleep and health that are modified by age. The fact that ageing alters the correlations of sleep duration with mortality risks, especially among men, is particularly salient.
Sleep difficulties, particularly inadequate habitual sleep length, are quite common in the general population. However, these are difficulties that rarely get discussed during doctor visits. Given the importance of this health domain, both patients and doctors are encouraged to address sleep difficulties as part of overall health.
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