Sleep and Your Cardiovascular Health
“O bed! O bed! delicious bed!
That heaven upon earth to the weary head.”
To Sleep, Perchance to Dream
We spend 1/3 of our lives sleeping (and the other 2/3 probably binge-watching Netflix). Even if you’re a “short sleeper,” a large part of the day is taken up by a phenomenon that we still know so little about (why we even need it in the first place is still debated).
Nevertheless, sleep is an infinitely important biological phenomenon, during which our bodies undergo many restorative processes; memory consolidation, mood regulation, clearance of brain metabolites, appetite regulation, immune/hormonal function, and tissue regeneration, among others.
While the cognitive and physical (performance) benefits of sleep have been well documented (as have the adverse effects of not getting enough), the profound consequences that sleep has on regulating, restoring, and maintaining the optimum functionality of the cardiovascular system have recently been getting more attention. Sleep, we now know, is a time during which profound modification of the cardiovascular system occurs. This modification serves a purpose — we don’t just “turn off” or “slow down” during sleep. In fact, during some aspects of sleep (such as REM), some common physiological processes are actually enhanced (for example, your blood pressure and heart rate increase).
As such, the processes that occur during sleep to maintain systemic CV health, including a lowering of heart rate and arterial blood pressure (during non-REM sleep) serve to give our bodies a “break” from the high cardiac output, stress on the heart, and pressure demands on our blood vessels and organs that we encounter during the day. A withdraw in sympathetic nervous system activity(the system that regulates the “fight or flight” response) and an increase in parasympathetic activity (sometimes called the system for “rest and digest”) accounts for these nocturnal happenings.
What happens when these systems go awry — when we either forgo sleep (voluntarily or involuntarily) for a certain period of time (say, 24 hours) or undergo a more chronic form of sleep deprivation/restriction, such as is seen in modern day society (we sleep profoundly less than we used to — with an almost doubling in the number of adults sleeping <6 hours in 2012 compared to 1985)?
Consequences of Insufficient Sleep: Your Achy Breaky Heart
Just 24 hour of wakefulness can have profound consequences for your cardiovascular health. Losing out on this period of restoration inhibits proper down regulation of many systems and can also lead to dysfunction while one is awake. Anyone who has gone without sleep for a prolonged period of time has undoubtedly experienced the cognitive issues and performance decrements associated with a sleep-deprived state. However, the cardiovascular consequences may be less obvious to our perception. Experimental studies have shown effects on the following parameters after just 24–40 hours of total sleep deprivation in healthy individuals.
Blood pressure
During sleep, blood pressure is normally reduced, termed “nocturnal dipping.” This decrease serves a healthy homeostatic function for humans . Inadequate sleep quantity or quality leads to an increase in blood pressure both during the night, as well as throughout the following day, most likely due to an increase in sympathetic activity (again, your “fight or flight” is constantly on, not a good thing). Accompanying this increase in blood pressure is an increase in heart rate — both at rest and most likely during any physical activity you might do the following day.
Inflammation
Inflammation is the body’s normal physiological immune response — mounting defensive molecules when an external stressor (e.g. virus or pathogen) is present. Improper inflammatory activation, either chronic or acute, is related to cardiovascular disease development and a slew of other metabolic disorders. During sleep deprivation, a variety of inflammatory markers increase: TNF-alpha, IL-6, C-reactive protein. Many of these (such as CRP) are independent predictors of cardiovascular disease and events. Inflammation leads to oxidative stress, and over time (situations of chronic sleep loss), this is a perfect primer for the development of cardiovascular disease development, among other disorders associated with low-grade inflammation.
Blood Vessel Function
The ability of your blood vessels to dilate is key in maintaining cardiovascular health, regulating blood pressure, and preventing development of disease. Asessment of blood vessel health in research involves subjecting the arteries to numerous stimuli, such as a large increase in blood flow to the arm, termed “reactive hyperemia,” or various agents such as sodium nitroprusside or even heat, which lead to the relaxation (vasodilation) or arteries. The responsiveness of the arteries to these stimuli tells us a lot about the health of the blood vessels. A decrease in function is often seen in many diseases such as CVD, obesity, and diabetes.
Sleep loss, whether acute or chronic, leads to a decrease in reactivity of blood vessels. Vascular conductance, one measure of micro-vessel reactivity, decreases after just 29 hours without sleep. This may be due to an increase in inflammation, a decrease in responsiveness of your vascular smooth muscle to certain molecules, or a heightened sympathetic activity (or likely, a combination of all of these). The body simply becomes less able to regulate blood vessel function properly. The consequence of this is that overall, we are able to less effectively perfuse our organs, tissues, and CV system. This is not insignificant — as endothelial function is directly related to cardiovascular disease risk, and even independently predicts disease development. Endothelial dysfunction after sleep loss, mirror that which occurs in numerous diseases, illustrates just how detrimental it may be.
Artery Stiffness
Our large arteries (such as the carotid) are, under healthy conditions, quite compliant (think, stretchy) — and hey need to be in order to properly regulate blood flow and blood pressure throughout the body. In pathological situations; aging, hypertension, obesity, smoking, among others, arteries can undergo “remodeling” whereby a number of molecular processes occur which lead to a stiffer, and less compliant blood vessel. Less compliant vessels result damage to organs, impaired blood flow, and are associated with a greater rate of death and disease from cardiovascular problems.
24 hours without sleep induces an increase in a measure of arterial stiffness termed pulse wave velocitiy (PWV), indicating a stiffer artery profile even after an acute bout of sleep loss. Chronic sleep loss, hypothetically, could lead to pathological remodeling over time — again, a prime candidate for CVD development.
Blood Clotting Factors
The incidence of cardiovascular disease events (such as heart attack and stroke) is known to be elevated in the morning, probably due to the large (and normal) morning surge in blood pressure and increase in blood coagulability. This occurs even in the absence of sleep loss or sleep deprivation.
Disrupted sleep (measured as sleep “efficiency” or fragmentation in sleep during the night) has been shown to associate with an increase in pro-thrombotic markers. Put simply, after a night of even sub-par sleep, markers of blood clotting such as von Willenbrand Factor (VWF) and soluble tissue factor (sTF) increase and may predispose even low-risk individuals to a cardiovascular event. Again, over time, this chronic pathological increase in thrombotic factors might just prime the body for the development of disease.
The 2017 Nobel Prize in Physiology and Medicine was recently awarded to Jeffrey C. Hall, Michael Rosbash and Michael W. Young for their discoveries of molecular mechanisms controlling the circadian rhythm. The implications of this award going to a topic dealing with the biological rhythms of our life (of which sleep is a major part) indicate the vast importance of the topic to human health and disease. This topic will become even more important in modern society, as we are now able to experience “24 hour days” involving constant stimulation — technology, illumination, and access to food whenever we wish. Sleep now seems to be something that individuals consider nuisance, a luxury, rather than a biological imperative. As a result, the health of our world is suffering, and the consequences on our productivity and well-being are becoming increasingly apparent.
Sleep loss and insufficient sleep might be given the titles of “silent” risk factors — given that up until now the importance of adequate restorative sleep has received relatively little attention. Additionally, the health consequences are not immediately realized (usually); even though some impairment is apparent early on, development of future disease may require longer periods (i.e. years) of insufficient sleep to fully manifest. However, as we realize the profound health consequences, both cardiovascular and otherwise, that insufficient sleep has, it will hopefully become a public health imperative, just as exercise and nutrition have.
Sweet dreams.
References
Trends in Self-Reported Sleep Duration among US Adults from 1985 to 2012. Sleep 38(5):829–32 (2015)
Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society on the Recommended Amount of Sleep for a Healthy Adult: Methodology and Discussion. Sleep. 38(8) 1161–1183 (2015)
CDC. Short Sleep Duration Among US Adults. https://www.cdc.gov/sleep/data_statistics.html
Sunbul et al. Acute sleep deprivation is associated with increased arterial stiffness in healthy young adults. Sleep Breath 18:215–220 (2014)
Tobaldini et al. Sleep, sleep depriavtion, autonomic nervous system, and caridovascular disease. Neuroscience and Biobehavioral reviews 74: 321–329 (2017)
Sauvet et al. Effect of acute sleep deprivation on vascular function in healthy subjects. Journal of Applied Physiology 108: 68–75 (2010)
von Kanel et al. Association between polysomnographic measure of disrupted sleep and prothrombotic factors. Chest 131(3) 2007, 733–739 (2007)
