An 11-study meta-analysis
Epameinondas Fountas, MD, of the Onassis Cardiac Surgery Center in Athens, presented a meta-analysis of 11 prospective studies of the relationship between daily sleep duration and cardiovascular disease morbidity and mortality published within the past 5 years, reflecting burgeoning interest in this hot-button topic. Collectively, the meta-analysis totaled 1,000,541 adults without baseline cardiovascular disease who were followed for an average of 9.3 years.
In an analysis adjusted for numerous known cardiovascular risk factors, the Greek investigators found that short sleep duration as defined by a self-reported average of less than 6 hours per night was independently associated with a statistically significant and clinically meaningful 11% increase in the risk of diagnosis of fatal or nonfatal cardiovascular disease, compared with individuals who averaged 6-8 hours nightly. Moreover, those who averaged more than 8 hours of sleep per night were also at risk: they averaged a 32% increased risk in fatal or nonfatal cardiovascular events compared to normal 6- to 8-hour sleepers. Thus, 6-8 hours of sleep per night appears to be the sweet spot in terms of cardioprotection.
“Our message to patients is simple: Sleep well, not too long, nor too short, and be active,” Dr. Fountas said.
Numerous investigators have highlighted the pathophysiologic changes related to sleep deprivation that likely boost cardiovascular risk. These include activation of the sympathetic nervous system, increased inflammation, and disrupted glucose metabolism, he noted.
Swedes weigh in
Moa Bengtsson, a combined medical/PhD student at the University of Gothenburg (Sweden), presented a prospective study of 798 men who were 50 years old in 1993, when they underwent a physical examination and completed extensive lifestyle questionnaires that included average self-reported sleep duration. Among the 759 men still available for evaluation after 21 years, or nearly 15,000 person-years of followup, those who reported sleeping an average of 5 hours or less per night back at age 50 were 93% more likely to have experienced a major cardiovascular event by age 71 -- acute MI, stroke, coronary revascularization, heart failure hospitalization, or cardiovascular death -- compared with those who averaged 7-8 hours of shut eye.
The short sleepers had a higher prevalence of obesity, diabetes, hypertension, smoking, and physical inactivity than the men who slept 7-8 hours per night. However, these and other confounders were adjusted for in the multivariate analysis.
To place sleep abnormalities in context, Ms. Bengtssen observed that short sleep in the Gothenburg men was numerically a stronger independent risk factor for future cardiovascular events than obesity, which was associated with an 82% increase in risk, or even smoking, with a 70% increase in risk.
Men who averaged either 6 hours of sleep per night or more than 8 hours were not at increased cardiovascular risk over 21 years of followup, compared with those who slept 7-8 hours.
Like the other investigators, she noted that the studies presented at the meeting, despite their extensive adjustments for potential confounders, don’t prove a direct causal relationship between short sleep and increased cardiovascular risk. An informative next step in research, albeit a challenging one, would be to show whether improved long-term sleep habits favorably alter cardiovascular risk.
All three study investigators reported having no financial conflicts regarding their research, which was conducted free of commercial support.