Risk of Cardiovascular Disease Increases with Daytime Napping

A team of investigators led by Zhiyu Wang, MPH, Department of Epidemiology and Biostatistics, School of Public Health, Tianjin Medical University, aimed to further understand the relationship between sleep and cardiovascular diseases (CVDs) by focusing on the characteristics of sleep.

The specific characteristics examined in conjunction with cardiovascular diseases were nighttime sleep duration, daytime napping, and sleep patterns. Additionally, investigators sought to determine if genetic and early-life environmental factors impacted this association.

Sleep patterns were assessed by sleep duration, chronotype, insomnia, snoring, and daytime sleepiness and were self‐reported at baseline along with sleep duration and napping. A total of 12,268 twin individuals who had no cardiovascular diseases were followed up to 18 years to identify any incident CVDs.

Patient information on cardiovascular disease was gathered from the Swedish National Patient Registry and the Cause of Death Register. Following the collection of data, investigators utilized a Cox model for analysis.

Associations of the Analysis

The average sleep duration was 8.5 hours per night from the overall study population, with an average baseline age of 70.3 years.

The multi-adjusted model analysis indicated that the ideal duration of sleep was 7-8 hours per night, in which no significant correlation was found in terms of cardiovascular disease risk. However, a shorter or longer sleep duration did exhibit an increased likeliness for cardiovascular diseases.

Additionally, Napping for any duration of time was associated with cardiovascular diseases, while the subpopulation that abstained from napping did not have the same significant association.

The Combined Effect of Nighttime Sleep and Daytime Napping

The most vulnerable to cardiovascular diseases appeared to be the subpopulation who slept less than 7 hours at night and took a daytime nap for more than half an hour, particularly compared with the population that received adequate sleep and forwent napping.

Although, those who achieved adequate sleep still displayed a higher risk for CVDs if they also engaged in daytime napping. Ultimately, investigators reported that the overall multiplicative interaction between nighttime sleep duration and daytime napping was not significant.

Overall Cardiovascular Risk Assessment

• Short and long nighttime sleep duration along with daytime napping 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, revealed an association.
• Investigators are not convinced that genetic and early‐life environmental factors are responsible for the sleep–CVD correlation.

"Because genetic or early‐life environmental factors can influence sleep habits and cardiovascular health, it is important to consider these unmeasured factors when evaluating the sleep–CVD association," investigators acknowledged. "To our knowledge, this is the first twin study to explore the effects of genetic and early‐life environmental factors on the association between sleep and CVDs. We found that genetic and early‐life environmental factors may not account for such association."

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