Scientific Overview on the Impact of Sleep on Health and Consciousness
Based on peer reviewed articles on all the health risks of not getting enough quality sleep
By Dr. Dan Gartenberg
Last Updated: March 30, 2023
In this overview of the impact of poor sleep on our health and consciousness, we will explore both how sleep deprivation and poor sleep quality impact almost every organ in the body. Additionally, sleep plays a role in most of the major chronic health diseases our society. There is both correlational and causal evidence that links sleep deprivation with cancer, heart disease, type II diabetes, hypertension, low immunity, Alzheimer's disease and more. Not getting enough sleep also impacts our mood, happiness, and even our sense of humor. Read on to learn about all the evidence regarding the importance of sleep and health. In the below report, both the correlational evidence supporting the links between sleep and disease will be discussed, in addition to the causal evidence. A convergence of both correlational and causal evidence suggests a very strong basis for the relationship.
Impact of not getting enough sleep or quality sleep
NOT ENOUGH SLEEP
About 40% of Americans are simply not getting enough sleep. A consensus report from the American Academy of Sleep Medicine states that adults need 7-9 hours on a regular basis. Yet many of us are getting by on far less sleep. Short sleepers, an extreme type of sleep deprivation, is defined as individuals who typically get 5 hours or less of sleep on a regular basis. Short sleep has been linked to: hypertension, stroke, cardiovascular disease, type 2 diabetes, cancer, Alzheimer’s disease, lower immunity, increased anxiety, increased depression, lower productivity, increased accidents, riskier decision making, decreased empathy, lower reaction time.
NOT ENOUGH DEEP SLEEP
Recent scientific research has demonstrated the importance of the deep stage of sleep, or slow-wave-sleep (SWS), in health and longevity. Deep sleep has been linked to less cerebral spinal fluid, less human growth hormone, and less clearance of neuronal metabolic waste that is thought to be associated with conversion to Alzheimer’s disease and related dementias.
The Links Between Sleep and Hypertension
CORRELATIONAL EVIDENCE
Two studies were conducted to examine the relationship between sleep duration and high blood pressure. The first study involved 25,352 Americans between the ages of 18-85 and found that having less sleep is linked to a higher likelihood of high blood pressure, particularly among African Americans. The second study involved 5,393 Korean adults between the ages of 19-99 and found that those who slept less than 5 hours per night had a 1.3 times greater risk of high blood pressure, even after taking into account other factors that could contribute to the condition. This effect is more pronounced among middle-aged adults and women.
CAUSAL EVIDENCE
Not getting enough sleep can increase blood pressure and heart rate, making our bodies work harder to maintain a healthy equilibrium. On the other hand, getting more sleep can lower blood pressure. Having an irregular sleep schedule can also affect our body's natural rhythm and increase variability in blood pressure.
High blood pressure is a leading risk factor for stroke and heart attacks.
The Links Between Sleep and Cardiometabolic Disease
CORRELATIONAL EVIDENCE
Research has shown that not getting enough sleep can increase the risk of cardiometabolic diseases, especially for overweight and obese individuals. A study of 239,896 US men and women aged 51-72 found that short sleep was linked to cardiometabolic disease. Short sleep and sleep disorders are also associated with an increased risk of adverse cardiometabolic effects. Japanese factory workers who slept less than seven hours per night tended to snack more between meals, have irregular eating habits, and prefer unhealthy, flavorful foods instead of vegetables. Moreover, there is a 24% increase in hospital visits for heart attacks during daylight savings time.
CORRELATIONAL EVIDENCE
Lack of sleep can lead to unhealthy eating habits, weight gain, and reduced physical activity, according to sleep restriction studies. Feeling tired can also affect our ability to make healthy food choices. Changes in hormones that regulate appetite can also occur. Neuroimaging studies show that our brain's reward system responds differently to food when we are sleep-deprived. Even just 30 minutes of sleep deprivation can have an impact. Additionally, blood tests have shown that lack of sleep can activate pro-inflammatory pathways in our bodies.
Metabolic syndrome is a cluster of conditions that increase the risk of heart disease, stroke, and diabetes.
The Link Between Sleep and Type 2 Diabetes
CORRELATIONAL EVIDENCE
Research has shown that not getting enough sleep can increase the risk of developing glucose intolerance and type 2 diabetes. A study of 722 men and 764 women aged 53-93 found that those who slept less than six hours were about 1.50 times more likely to develop glucose intolerance and type 2 diabetes than those who slept more than three hours. A meta-analysis of 10 studies that included 447,124 adults aged 45 and over found that people who slept less than seven hours per night were about 30% more likely to develop diabetes. Additionally, people with diabetes are about twice as likely to die from heart attack or stroke. Various sleep issues, such as short or long sleep, insomnia, and sleep disordered breathing, have all been correlated with an increased risk of diabetes.
CAUSAL EVIDENCE
Studies have shown that not getting enough sleep can have negative effects on our body's ability to regulate glucose and insulin levels. Experimental sleep restriction has been found to cause impaired glucose tolerance and insulin sensitivity. Sleep debt, which occurs when we consistently do not get enough sleep, can also harm our body's ability to regulate carbohydrate metabolism and endocrine function. A misaligned circadian rhythm, or sleep schedule, can also impact our endocrine function. It's important to get enough sleep and maintain a regular sleep schedule to avoid these negative impacts on our body's functioning.
The Link Between Sleep and Cancer
CORRELATIONAL EVIDENCE
There is mixed evidence on whether too much or too little sleep is linked to cancer risk. However, a study of over 1.5 million Asian participants found strong evidence that short sleep (less than 7 hours per night) is associated with an increased risk of cancer. Long sleep duration (more than 9 hours per night) has also been found to be associated with certain types of cancer, but this may be a correlation rather than a causation. Overall, it's important to maintain a healthy sleep schedule to reduce the risk of cancer.
CAUSAL EVIDENCE
Studies have shown that lower levels of melatonin, a hormone that regulates sleep, can lead to increased levels of estrogen which is linked to certain types of breast cancer. Additionally, disruption of the body's circadian rhythm has been linked to deregulated cell proliferation and the progression of cancer. It's important to maintain healthy sleep patterns to help regulate hormone levels and reduce the risk of developing certain types of cancer.
The Link Between Sleep and Immunity
CORRELATIONAL EVIDENCE
For 2500 years, it has been known that sleep can help fight sickness. When we are sick, we often feel the need to sleep more, and this is because our bodies use sleep to fight off pathogens.
CAUSAL EVIDENCE
Getting enough sleep is crucial for maintaining a healthy immune system. When we sleep, our body produces proteins called cytokines that help cells communicate with each other and initiate the production of antibodies to fight off disease. Poor sleep can lead to inflammation and weaken the ability of immune cells to fight viruses, as shown by Dr. Monika Haack at Harvard. However, healthy sleep prior to a vaccine can increase the number of antibodies produced, leading to a better response to the vaccine. Deep sleep is especially important for building a healthy immune system.
The Link Between Sleep and Alzheimer's Disease
CORRELATIONAL EVIDENCE
A study of 737 people without dementia found that sleep fragmentation increased the risk of developing Alzheimer's disease by 1.5 times compared to individuals with healthy sleep. Alzheimer's patients experience more symptoms at certain times of the day, which is known as sundowning. Another study of 8,000 people in Britain found that 50-60 year olds who were sleep deprived had a 30% greater likelihood of being diagnosed with dementia. Maintaining healthy sleep habits can help reduce the risk of developing Alzheimer's disease and other forms of dementia.
CAUSAL EVIDENCE
In older adults, poor sleep is associated with a reduction in brain volume in areas related to Alzheimer's and related dementias. A study found that poor sleepers had a significant reduction in cortical and subcortical volumes in areas including the hippocampi, superior parietal lobules, and the left amygdala. Additionally, daytime sleepiness was found to increase the deposition of β-amyloid plaques associated with AD/ADRD. The explanation for these associations is that sleep deprivation disrupts the glymphatic clearance of beta-amyloid during sleep. It's important to maintain healthy sleep habits to reduce the risk of AD/ADRD.
Sleep Stage and Cleaning of the
Brain and Body
CORRELATIONAL EVIDENCE
A study showed that slow wave sleep (SWS) affects the accumulation of β-amyloid in certain regions of the brain in mice. This can potentially lead to Alzheimer's disease. The clearance of β-amyloid can be affected by chronic sleep deprivation, which impairs SWS. This can lead to inefficiencies in amyloid beta clearance and contribute to the development of Alzheimer's disease.
CAUSAL EVIDENCE
In deep sleep, the body produces cerebral spinal fluid and human growth hormone that helps clear waste from neurons. However, less deep sleep can lead to decreased levels of these substances, resulting in reduced clearance of waste from neurons. During non-rapid eye movement (NREM) slow-wave sleep (SWS), there is a reduction in the size of glial cells that increases the extracellular space and allows clearance of toxins and metabolites. Studies have shown that beta-amyloid clearance increases two-fold during NREM SWS compared to when we are awake. Therefore, deep sleep is crucial for the clearance of waste from the brain, including beta-amyloid, which is associated with Alzheimer's disease.
Summary of the Health Effects of Poor Sleep
The article discusses the impact of not getting enough sleep or quality sleep on different aspects of health. Lack of sleep has been linked to various health issues such as hypertension, stroke, cardiovascular disease, type 2 diabetes, cancer, Alzheimer's disease, lower immunity, increased anxiety, increased depression, lower productivity, increased accidents, riskier decision making, decreased empathy, and lower reaction time. The article provides both correlational and causal evidence for the links between sleep and these health issues. The article also highlights the importance of the deep stage of sleep and the role it plays in health and longevity. Overall, the article suggests that getting enough quality sleep is crucial for maintaining good health.