The Importance of Sleep Quality On Preventing Heart Disease
In light of cardiovascular disease being the leading cause of death in the world, there has been an increasing demand for uncovering potential causes to decrease future mortality. Recently, one study discovered a relationship between sleep fragmentation and atherosclerosis, representing a critical step in the right direction for preventing further development of heart disease.
Atherosclerosis is the hardening of blood vessels called arteries due to a buildup of plaque, which includes fat, cholesterol, and other cell waste products, on the artery walls. This disease can often lead to other cardiovascular issues, like coronary artery disease, that can cause heart attacks. The indirect relationship between sleep fragmentation and atherosclerosis is credited to the increased levels of neutrophils and monocytes—types of white blood cells—that result from a reduced quality of sleep. Monocytes and high levels of neutrophils, or neutrophilia, are generally a sign of infection, since an increase in these white blood cells indicates the body's immune system response to fight such infections.
In the study, the researchers used three main methods to collect data: wrist-based actigraphy, polysomnography (PSG), and monitoring of white blood cell levels. Actigraphy is a technique often used in sleep studies to monitor human motor activity over a period of time. This method, which was used for seven consecutive days, showed a strong positive correlation between sleep fragmentation and coronary artery calcification (CAC) score, a measurement of calcium buildup in the arteries. This correlation was indirectly facilitated by increased neutrophil levels. A higher CAC score is indicative of a higher risk of developing heart disease.
Atherosclerosis is the hardening of blood vessels called arteries due to a buildup of plaque, which includes fat, cholesterol, and other cell waste products, on the artery walls. This disease can often lead to other cardiovascular issues, like coronary artery disease, that can cause heart attacks. The indirect relationship between sleep fragmentation and atherosclerosis is credited to the increased levels of neutrophils and monocytes—types of white blood cells—that result from a reduced quality of sleep. Monocytes and high levels of neutrophils, or neutrophilia, are generally a sign of infection, since an increase in these white blood cells indicates the body's immune system response to fight such infections.
In the study, the researchers used three main methods to collect data: wrist-based actigraphy, polysomnography (PSG), and monitoring of white blood cell levels. Actigraphy is a technique often used in sleep studies to monitor human motor activity over a period of time. This method, which was used for seven consecutive days, showed a strong positive correlation between sleep fragmentation and coronary artery calcification (CAC) score, a measurement of calcium buildup in the arteries. This correlation was indirectly facilitated by increased neutrophil levels. A higher CAC score is indicative of a higher risk of developing heart disease.
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PSG is another test often used with sleep studies that monitors brain activity, breathing, and blood oxygen levels. Using this method, sleep fragmentation was measured by the number of arousals (sleep interruptions) during non-rapid eye movement (NREM) sleep. Researchers found that increased fragmentation predicted a higher CAC score as a result of increased levels of neutrophils and monocytes. Thus, it was concluded that the pathway in which reduced sleep quality leads to atherosclerosis is mediated by inflammation caused by an increased white blood cell count.
Such results, however, were distinct to NREM sleep and did not apply to rapid eye movement (REM) sleep, suggesting that interruptions during NREM sleep have a greater impact on the potential development of atherosclerosis and subsequently, cardiovascular disease. NREM sleep encompasses the first few stages of sleep and is characterized by progressively deeper sleep with each passing stage, whereas REM sleep is the deepest and last sleep stage before the cycle repeats. Therefore, the results from the study indicate the importance of sleeping without any distractions, as interruptions in the initial stages of sleep may be the most detrimental when considering heart disease.
It must be noted, however, that the study was limited by its use of cross-sectional data as opposed to using longitudinal data, which introduced the possibility of confounding variables. Despite this, even after considering different factors known to increase the risk of atherosclerosis, such as age, sex, and blood pressure, the study showed that increased levels of neutrophils and monocytes can be due to sleep fragmentation, raising atherosclerosis risk. While the particular mechanism which links sleep fragmentation and atherosclerosis is still being explored, these findings nevertheless suggest that improving sleep quality may be a potential route to lowering rates of cardiovascular disease in the future.
Such results, however, were distinct to NREM sleep and did not apply to rapid eye movement (REM) sleep, suggesting that interruptions during NREM sleep have a greater impact on the potential development of atherosclerosis and subsequently, cardiovascular disease. NREM sleep encompasses the first few stages of sleep and is characterized by progressively deeper sleep with each passing stage, whereas REM sleep is the deepest and last sleep stage before the cycle repeats. Therefore, the results from the study indicate the importance of sleeping without any distractions, as interruptions in the initial stages of sleep may be the most detrimental when considering heart disease.
It must be noted, however, that the study was limited by its use of cross-sectional data as opposed to using longitudinal data, which introduced the possibility of confounding variables. Despite this, even after considering different factors known to increase the risk of atherosclerosis, such as age, sex, and blood pressure, the study showed that increased levels of neutrophils and monocytes can be due to sleep fragmentation, raising atherosclerosis risk. While the particular mechanism which links sleep fragmentation and atherosclerosis is still being explored, these findings nevertheless suggest that improving sleep quality may be a potential route to lowering rates of cardiovascular disease in the future.
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