Posted on Dec 05, 2018, 9 a.m.
Sleep and Cardiovascular Disease
Heart Health VIII
Sleep and Cardiovascular Disease
During my cardiology training 30 years ago, the only mention of sleep and cardiovascular disease (CVD) was the sleep we were missing as fellows and the rare massively obese patient with hypoventilation (Pickwickian Syndrome) and end-stage cor pulmonale (1).
The recognition of much more subtle sleep abnormalities as a risk factor for CVD has grown tremendously in the last decade. The study that brought this to my attention was the MORGEN study (2). In this population-based cohort study over 10-15 years in 20,432 Danish men and women, sleep duration and quality was one of the potential risk factors for developing CVD in follow-up. In analyzing the 1,486 cases of CVD that developed, short sleepers (<6 hours) had a 15% higher risk compared to normal sleepers (7 hours) after adjustment for all known cofounders. Of even more concern was those that indicated short sleep of poor quality and they had a 63% higher risk of CVD compared to normal sleepers of good sleep quality.
Enough data has been reported on the topic to warrant meta-analysis (3). In an evaluation through January 2016, reports involving 17,841 cases of coronary heart disease (CHD) amongst 517, 440 participants were available. The lowest risk of developing CHD was in those sleeping 7-8 hours a day. For any reduction of 1 hour of sleep below 7 hours the risk increased significantly (HR 1.11) and also for any increase above 8 hours the risk also increased (HR 1.07).
A large study population was reported recently from Hong Kong adding more appreciation of the role of sleep quality and CVD (4). The study examined 60,586 adults who filled out sleep questionnaires and were followed for the development of CHD. Participants with sleep durations averaging <6 hours had an increased risk of CHD with a hazard ration of 1.13. The risk for those sleeping >8 hours did not reach statistical significance but was 1.11. Poor sleep quality described as “dreamy” sleep or difficulty falling asleep requiring sleeping pills or other drugs increased the risk for CHD (HR 1.40). Again, the combination of short sleep and poor-quality sleep was the highest risk.
One possible explanation for the association of a higher risk for CVD with poor sleep quality may be a higher risk of diabetes mellitus in those with poor sleep (5). Over 16,000 men and women in the Malmo Diet Cancer Study without diabetes mellitus or CHD were followed for 14-16 years after filling out information about sleep habits. In men, a sleep duration <6 hour was associated with incident diabetes (HR 1.35), CHD (HR 1.41), and both diabetes/CHD (HR 2.34). Long sleep duration >9 hours was associated with diabetes (HR 1.37), CHD (HR 1.33), and the combination of both (HR 2.1). Similar trends were found in women participants in the study. The researchers concluded that the associations between sleep duration and CHD may reflect associations between sleep and incident diabetes mellitus.
While not all cases of poor sleep duration and quality are due to obstructive sleep apnea (OSA), the importance of early diagnosis and treatment of OSA cannot be overstated. Studies seeking to demonstrate a reduction in CVD in patients treated for OSA with CPAP have provided mixed results (6). A recent review and meta-analysis of studies through late 2017 selected 2 randomized clinical trials and 7 observational trials including 1430 participants with CHD. The median follow-up varied from 36 to 86 months. In 6 observational studies, treatment with CPAP was associated with a lower risk of cardiac events but this was not found in the 2 randomized trials. In the observational studies that tracked all-cause and CVD deaths, a reduction in events with CPAP was reported but this was not confirmed in the 2 randomized studies. In a separate review and meta-analysis of patients with OSA, therapy with CPAP could also not be confirmed to reduce the risk of CVD outcomes or death (7).
Overall, it is clear that both optimal sleep duration and sleep quality are goals of CVD therapy and prevention. The availability of home sleep tests, convenient for patients and cost-effective, has increased the numbers of patients identified with OSA and other sleep disorders (8). Even though a reduction in mortality has not been confirmed in trials of treating OSA with CPAP, many other benefits may accrue from natural and integrative approaches to improved sleep including executive function and physical performance (9).