Imagine waking up feeling refreshed, energized, and ready to conquer the day — every single day. In today's fast-paced world, sleep often takes a backseat to productivity. But, the irony is striking: sacrificing sleep to pursue productivity and success can sabotage our health, happiness, and even our longevity.
Quality sleep is a cornerstone of longevity, yet many adults struggle to get enough rest. Despite its critical importance, one in three adults doesn't get enough sleep. A sleep deficit doesn't just make you feel groggy in the morning — it potentially shaves years off your life [1].
The key to a longer life (and a healthier one) is as simple as sleeping well.
This article discusses the science of sleep, exploring the intricate relationship between sleep quality, duration, and longevity. You'll discover the optimal amount of sleep for longevity and why both too little and too much sleep can impact your health.
What’s Happening While You’re Asleep?
Sleep is a complex process. While we may appear inactive during sleep, our bodies and brains are engaged in critical functions throughout the night.
Circadian Rhythms
Your circadian rhythms are a 24-hour cycle that dictates your body's internal clock. They control your body's sleep-wake cycle and regulate your body temperature, heart rate, and hormone levels. Let's explore each of these three roles and how they affect sleep [2]:
- Hormone levels: Light exposure largely influences the sleep-wake cycle, signaling hormone production. Darkness signals sleepiness to the brain, releasing melatonin to make you feel tired. Light signals that it's daytime, releasing cortisol for energy.
- Body temperature: Body temperature tends to be higher during the day and cools off at night. The body loses heat (and decreases heat production) at night, promoting sleep onset.
- Heart rate: Changes in heart rate occur at night. Heart rate tends to decrease, so the body is relaxed and prepping for sleep.
Stages of Sleep
Throughout the night, your body cycles through different stages of sleep: deep sleep, REM sleep, light sleep, and awake. Each of these sleep cycles is responsible for key repair processes in the body [3].
- Light sleep: This is generally the phase of sleep we spend the most time in, about 50%. It serves as a transition between deep and REM sleep.
- Deep sleep: Also known as slow wave sleep, this phase slows brain waves and nervous system activity. Deep sleep is physically restorative and serves as a time for the body to recover and repair from physical activities. Most deep sleep occurs at the beginning of the night. The body spends about 20% of the night in deep sleep.
- REM sleep: Unlike deep sleep, REM sleep is a time of heightened brain activity. In fact, the brain is nearly as active as it is during the day. This is when the brain restores mentally. The brain takes short-term memories, like what happened during the day, and reinforces them into long-term memories. REM sleep accounts for about 20% of your overall sleep.
- Awake time: This accounts for the time it takes you to fall asleep (or fall back asleep) throughout the night. Aim to make your awake time less than 15% of your total sleep time.
How Much Sleep Do You Need For Longevity?
Many studies show that there is a “sweet spot” amount of sleep to aim for each night — with consensus centering around getting seven to nine hours for a longer life [4].
Large meta-analyses (a type of study that pools data from multiple other studies on a given topic) find that getting too little and too much sleep is correlated with an increased risk of all-cause mortality (early death). Let’s dive into what these studies have shown.
A meta-analysis of 16 studies, including over 1.3 million participants, looked at sleep data and its effect on all-cause mortality. During the study period, there were over 112,000 deaths. Compared to sleeping for 6-9 hours per night, sleeping for less than six hours was associated with a 12% increased risk of death. The study also found that sleeping for longer than nine hours per night was associated with a 30% higher risk of death than those sleeping six to nine hours nightly. However, the relationship between longer sleep duration and increased mortality risk is not necessarily causal. Confounding factors, such as underlying health conditions, may contribute to the longer sleep durations observed in some individuals [5].
Another analysis, including 40 studies and over 2.2 million participants, yielded similar findings. Compared to sleeping for seven hours per night, sleeping from four to six hours per night was associated with a 4-6% increased risk of death. Similarly, the study found that sleeping nine to ten hours per night was associated with a 13-25% increased risk of death (compared to those who sleep seven hours per night) [6].
Yet another study found that too much and too little sleep is associated with an increased risk of death. This meta-analysis included 67 studies and over 3.5 million participants. They found that the lowest risk of death centered around sleeping seven hours per night. Each hour of sleep below sleeping for seven hours per night was associated with a 6% increased risk of death. Each hour above this amount was associated with a 13% increased risk of death [7].
The same study also found that too little and too much sleep was associated with an increased risk of total cardiovascular (heart) disease, coronary heart disease, and stroke [7].
Getting Quality Sleep: Why Sleep Quality Matters, Too
While the amount of sleep you get is a determinant of health, the quality of your sleep contributes to your overall health and well-being, too [8].
Sleep quality can be assessed through both objective and subjective measures, drawing a comprehensive picture of your sleep health.
Objective Measures of Sleep Quality
Quantifiable, objective aspects of sleep are often measured through sleep-tracking devices. Here are a few metrics they commonly monitor [9]:
- Sleep Latency: This refers to how long it takes you to fall asleep. Ideally, it should take between 10 to 20 minutes. Falling asleep too quickly may indicate sleep deprivation, while taking too long may suggest that your body isn't quite relaxed yet.
- Awakenings: This is the number of times you wake up during the night. It's normal to have brief awakenings, but frequent or prolonged ones can disrupt your sleep cycle and impact overall sleep quality.
- Wake After Sleep Onset (WASO): This measures the amount of time you spend awake after initially falling asleep. A high WASO value can indicate poor sleep quality or potential sleep disorders.
- Sleep Efficiency: This is the ratio of time spent asleep, compared to the total time spent in bed. Aim for a sleep efficiency above 85%. For example, if you spend 8 hours in bed and sleep for 7 hours, your sleep efficiency would be 87.5%.
Subjective Measures of Sleep Quality
There are also subjective or perceived measures of sleep quality. These are typically captured through validated, self-reported questionnaires.
- Perceived Sleep Quality: Your overall feeling about how well you slept is your perceived sleep quality. It can include factors like how refreshed you feel upon waking or how satisfied you are with your sleep.
- Feeling Relaxed: Your feelings of physical and mental relaxation when you wake up can indicate sleep quality.
- Daytime Functioning: How you feel and function during the day can reflect your sleep quality. Good sleep typically leads to a better mood, alertness, and cognitive performance.
Research shows that both objective and subjective measures contribute to our total sleep quality [9].
A recent study highlighted the importance of considering both objective and subjective measures when assessing sleep quality, as they can provide complementary information about an individual's sleep health [8].
Understanding and monitoring these aspects of sleep quality can help you identify areas for improvement in your sleep habits and potentially flag any developing sleep issues. Good sleep quality is as important as quantity for optimal health and well-being.
Health Benefits of Getting Quality Sleep (And Risks of Sleep Deprivation)
Sleep is a fundamental pillar of health, influencing nearly every aspect of our well-being. The quality and quantity of our sleep can profoundly affect our physical and mental health.
Let's examine the health benefits of getting quality sleep and the risks of sleep deprivation. These highlight why prioritizing good sleep habits is crucial for overall health and longevity.
A Lack of Sleep Impacts Heart Health
The effects of a few bad nights of sleep are apparent: poor mood, drowsiness, and irritability. However, a consistent lack of sleep can impact long-term health, including poor heart health.
A lack of sleep is associated with an increased risk of cardiovascular diseases, including hypertension, coronary heart disease, and stroke [10].
When we don't get enough sleep, inflammation levels rise, stress elevates, and metabolism changes. These factors (among others) contribute to the development of heart-related issues. Studies consistently show that a lack of sleep is associated with an increased risk of heart disease [10].
Poor Sleep Slows Metabolism
An estimated 7% of the adult population in the US is considered metabolically healthy [11]. That's less than 1 of every 13 adults. Many factors influence metabolism, from what you eat to how you move and especially how you sleep.
Getting consistent poor sleep impacts many metabolic processes, most notably, blood sugar control. Blood sugar control is closely tied to metabolic conditions like type 2 diabetes. And studies show that a lack of sleep increases the risk of developing type 2 diabetes [12, 13].
A lack of sleep can also impact appetite-related hormones like leptin and ghrelin. Leptin signals that you're full and satiated, decreasing your appetite. Ghrelin increases your appetite, letting your body know it's time to eat. A lack of sleep throws these hormones out of balance, reducing leptin and increasing ghrelin, making you feel hungry [12, 14].
Better Sleep Improves Memory
During sleep, the brain repairs and strengthens itself, improving cognitive function. Consistent, quality sleep is associated with having a better memory [15].
REM sleep, in particular, is essential for brain health, as the brain consolidates memories during this sleep phase. For example, a recent memory gets consolidated into a long-term memory so you can remember it. The neural connections that create long-term memories are strengthened during sleep [15].
On the other hand, not getting enough sleep can impact mood and cognition. Even short-term sleep deprivation (for one day) can lead to mood changes and confusion [16].
Poor Sleep = More Stress, and Vice Versa
On the night before a big exam or presentation, you may feel stressed, making it challenging to fall asleep. Stress can impact your ability to fall and stay asleep. And on the other hand, a lack of sleep can increase stress levels during the day [17].
Stress and sleep have a bidirectional relationship, each significantly influencing the other. When stress levels are high, the body releases the "stress hormone" cortisol into the body. Cortisol is responsible for kicking off processes that give you energy to "fight" the stressor at hand. So, a cortisol increase can disrupt your sleep-wake cycle, making it harder to fall asleep [18].
Poor sleep also increases stress levels, creating a loop. Sleep deprivation can lead to poor mood and cognitive disturbances, making coping a challenge [17].
Immune Health Strengthens During Sleep
Sleep plays a vital role in maintaining and enhancing immune function. During sleep, the immune system releases molecules called cytokines that help fight infection and inflammation (that also promote sleep) [19].
Sleep deprivation can suppress immune function, making you more susceptible to infections and increasing inflammation. Losing sleep over time is linked to increased inflammation, a common risk factor for conditions like heart disease, diabetes, and certain cancers [20].
Hormone Regulation
Sleep and hormone levels are highly related. While asleep, the body regulates the production and release of hormones like growth hormone, testosterone, and cortisol. These hormones play crucial roles throughout the body, like growth and repair, stress regulation, blood sugar balance, appetite control [21].
A lack of sleep is associated with lower testosterone and higher cortisol levels, creating a hormone imbalance where the body is breaking down muscle rather than building it. [22].
Hormone imbalances can also impact sleep quality and duration. High cortisol levels due to stress can lead to insomnia, and changes in reproductive hormones like estrogen and progesterone can affect sleep patterns in women [23].
This intricate interplay between sleep and hormones underscores the importance of maintaining healthy sleep habits.
Key Takeaways
- Aim for 7-9 hours of sleep per night for optimal health and longevity: Getting too little and too much sleep are associated with a shorter lifespan
- Sleep quality is as important as quantity for overall health
- Poor sleep is linked to increased risks of cardiovascular disease, metabolic disorders, and cognitive decline
- Consistent sleep and wake times help regulate your circadian rhythm
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