Those in the lowest quartile for duration of SWS had almost twice the risk of high blood pressure (BP) compared with those in the highest quartile, even after adjustment for all potential confounders, including other sleep disorders, say Dr Maple M Fung (San Diego Veterans Affairs Healthcare System, CA) and colleagues in their paper published online in Hypertension.
"This article adds to the growing body of literature that associates sleep architecture with metabolic and physiologic changes that may reflect altered neurohormones and inflammatory markers," note the authors. "Further studies are needed to confirm these observations . . . and determine whether modifications in SWS improve hypertension."
"Our study shows for the first time that poor quality sleep, reflected by reduced slow wave sleep, puts individuals at significantly increased risk of developing high blood pressure, and that this effect appears to be independent of the influence of breathing pauses during sleep," says coauthor Dr Susan Redline (Brigham and Women's Hospital, Boston, MA) in a statement by the American Heart Association [2].
Restorative SWS May Influence Nocturnal BP
Fung and colleagues explain that human sleep is divided into rapid eye movement (REM) and nonREM (NREM) sleep, and that NREM is further divided into three stages: N1, N2, and N3. N3, also known as SWS, is restorative and the stage associated with the highest arousal threshold.
SWS has been implicated in memory and overnight improvements in perceptual and visuomotor performance and learning, but its full importance remains to be elucidated, say the researchers. SWS has also been associated with transient metabolic, hormonal, and physiological changes that affect glucose metabolism, and is associated with decreased sympathetic nervous system activity and increased vagal tone. "These, in turn, are associated with decreased heart rate and blood pressure, which may influence nocturnal BP profiles. The disappearance of a nocturnal 'dipping' BP pattern is known to increase the risk of hypertension and CVD," they observe.
In their study--in which polysomnography was used to monitor measures of sleep-disordered breathing, sleep duration, and sleep architecture--Fung and colleagues followed 784 community-dwelling men aged >65 years (mean 75.1 years), who participated in the Outcome of Sleep Disorders in Older Men study and did not have hypertension at the time of their in-home polysomnography (2003–2005). Participants completed questionnaires to assess demographics and other risk factors.
The men returned for follow-up in 2007–2009; 243 met the criteria for incident hypertension (>140/90 mmHg), after a mean follow-up of 3.4 years.
After adjustment for age, nonwhite race, study site, and body mass index, the only sleep index to remain significantly associated with incident hypertension was percentage of SWS (odds ratio 1.83 for lowest to highest quartile of SWS). No further attenuation of this association was seen after accounting for sleep duration, sleep fragmentation, and indices of sleep-disordered breathing.
SWS May Be the Critical Component Affecting BP
"To our knowledge, this is the first large-scale analysis of comprehensive polysomnography data that assesses the association of indices of three key sleep domains: sleep-disordered breathing (apnea), sleep duration, and sleep architecture to incident hypertension in an elderly cohort," say the authors.
"Our study suggests that a specific reduction of SWS rather than nonspecific sleep disruption may be a . . . critical factor that influences BP," they conclude.
Redline says: "People should recognize that sleep, diet, and physical activity are critical to health, including heart health and optimal blood pressure control. Although the elderly often have poor sleep, our study shows that such a finding is not benign. Poor sleep may be a powerful predictor for adverse health outcomes. Initiatives to improve sleep may provide novel approaches for reducing hypertension burden."
Fung discloses previous grant support from Forest Laboratories, and currently owns stock and is employed by Amgen. Coauthor Anconi-Israel is a consultant for Ferring Pharmaceuticals, GlaxoSmithKline, Johnson & Johnson, Merck, NeuroVigil, Pfizer, Philips, Purdue Pharma LP, Sanofi-Aventis, and Somaxon Pharmaceuticals.
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