Latest research presented at this year’s European Association for the Study of Diabetes (EASD) meeting in Munich, Germany (12-16 Sept) shows that daytime naps of over 1 hour or more increase the risk of developing type 2 diabetes by 45% compared with no napping. There is no increased risk caused by naps shorter than 60 minutes. The study is by Dr Yamada Tomahide, University of Tokyo, Japan, and colleagues.
Sleep is an important component of a healthy life, along with a good diet and appropriate physical activity. Several recent studies have shown that a U-shaped curve describes the relation between the duration of sleep (hours of sleep/night) and metabolic diseases. However, some people cannot get enough sleep at night due to social life and work life related factors. Taking naps is widely prevalent around the world. Daytime naps are usually brief, but can range from a few minutes to a few hours. The frequency varies from taking an occasional nap to planned rest periods even several times daily for habitual nappers. Some individuals take a nap because they are excessively sleepy during the daytime as a result of a sleep disorder.
In this study, the authors performed a meta-analysis to investigate the association between napping and the risk of metabolic diseases, and to quantify the potential dose-response relationship. They searched electronic databases for articles published up to 2016. To ascertain the validity of the eligible studies, the quality of each report was appraised with reference to the STROBE statement. In addition, a tool called the Newcastle-Ottawa Scale for assessing the quality of observational studies in meta-analyses was used to assess the validity of each study.
The analysis included 307,237 Asian and Western across 21 reports. In each study, analyses were well adjusted for several confounders. Pooled analysis revealed that a longer nap (≥60 min/day) each significantly increased the risk of type 2 diabetes by 45% compared with no daytime napping. In contrast, a shorter nap (<60 min/day) did not. A dose-response meta-analysis showed a J-shaped relation between nap time and the risk of diabetes or metabolic syndrome, with no effect of napping up to about 40 minutes/day followed by a sharp increase in the risk at longer times, becoming clinically significant at 60 minutes onwards. However, analysis showed that nap time was not associated with an increased risk of obesity for either shorter or longer naps.
The authors conclude: “Longer nap was associated with increased risk of diabetes and metabolic syndrome. Further studies are needed to confirm the efficacy of a short nap.”