Risk of Cardiovascular Disease Increases with Daytime Napping

A team of researchers led by Zhiyu Wang, MPH, Department of Epidemiology and Biostatistics, School of Public Health, Tianjin Medical University, aimed to better understand the relationship between sleep and cardiovascular diseases (CVDs) by examining focused on the properties of sleep.

The specific characteristics examined in relation to cardiovascular disease were nighttime sleep duration, daytime naps, and sleep patterns. In addition, the researchers sought to determine whether genetic and early childhood environmental factors affected this association.

Sleep patterns were assessed for sleep duration, chronotype, insomnia, snoring, and daytime sleepiness, and were reported at baseline along with sleep duration and naps themselves. A total of 12,268 twins who did not have cardiovascular disease were followed up to 18 years of age to identify incidents of cardiovascular disease.

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Cardiovascular disease patient information was collected from the Swedish National Patient Registry and the Causes of Death Registry. After data collection, investigators used a Cox model for analysis.

Associations of Analysis

The mean sleep duration of the entire study population was 8.5 hours per night with a mean baseline age of 70.3 years.

The multiple-fit model analysis found that the ideal sleep duration is 7-8 hours per night, with no significant correlation found in terms of cardiovascular disease risk. However, a shorter or longer sleep duration showed an increased likelihood of cardiovascular disease.

Furthermore, napping was associated with cardiovascular disease for any length of time, while the napping-absent subpopulation did not have the same significant association.

The combined effect of nighttime sleep and daytime naps

The subpopulation that slept less than 7 hours at night and napped for more than half an hour during the day appeared to be the most vulnerable to cardiovascular disease, especially compared to the population that received adequate sleep and did not nap.

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However, those who achieved adequate sleep still showed a higher risk of cardiovascular disease when they also napped during the day. Ultimately, the researchers reported that the overall multiplicative interaction between nighttime sleep duration and daytime naps was not significant.

Overall cardiovascular risk assessment

  • Short and long night sleep durations as well as afternoon naps were associated with a moderate increase in risk.
  • Patterns consisting of negative sleep characteristics such as insufficient or excessive sleep, evening chronotype, frequent insomnia, heavy snoring and frequent daytime sleepiness showed an association.
  • Researchers are not convinced that genetic and early childhood environmental factors are responsible for the sleep-CVD correlation.
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“Because genetic or early childhood environmental factors can affect sleep patterns and cardiovascular health, it is important to consider these unmeasured factors when evaluating the association between sleep and cardiovascular disease,” the researchers acknowledged. “To our knowledge, this is the first twin study to examine the impact of genetic and early childhood environmental factors on the association between sleep and cardiovascular disease. We found that genetic and early childhood environmental factors may not be responsible for such an association.”

Association of Sleep Duration, Napping, and Sleep Patterns With Risk of Cardiovascular Diseases: A Nationwide Twin Study was published in Journal of the American Heart Association.

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