A few weeks ago, we wrote about hormonal changes that occur as we age. Two hormones that experience age-related declines are the key drivers of sleep: melatonin and cortisol. Changes in the availability of these signaling molecules eventually result in the characteristic sleepless nights that seem to increase in frequency the older we get.
This week we take a closer look at the connection between aging and sleep (or the increasing lack thereof). Why does it happen? What effects does it have on our bodies? And most importantly, what can we do about it?
Here is what we learned:
The Mechanics of Sleep
As normal bodily functions go, sleep is probably one of the most important for longevity. Adapting our lifestyles around our circadian rhythm and ensuring our bodies have a sufficient opportunity to recover from the strains of the prior day are intuitive building blocks for maximizing our healthspan. Sadly, sleep is also often the easiest ingredient to sacrifice when we are overly busy, feeling stressed out, or short on “me” time. We are probably preaching to the choir, but deprioritizing sleep can have serious short and long-term consequences not only on your physical and cognitive performance but on your long-term health outcomes. Scientists have yet to uncover all the reasons why we sleep, but energy conservation and restoration of body systems are two of the major reasons we need a good night’s rest.
We owe our sleep/wake cycle to the suprachiasmatic nucleus (SCN),the internal clock that sets our circadian rhythm. Under normal circumstances, light exposure and melatonin help regulate our internal clocks. While light alters our brains to whether it's daytime or night, melatonin acts as a catalyst for sleep causing drowsiness as the day progresses (i.e. “sleep pressure”).
Sleep occurs in four stages, each of which is defined by a noticeably different pattern in brain activity when measured on an EEG. The first three stages of sleep are non-REM or quiet sleep, while the fourth stage is REM or dreaming sleep. We cycle through the 4 stages in loops that last from 1½ to 2 hours and we do so multiple times during a 7-8 hour sleeping period
Check out this 2-minute video we found on the neuroscience of sleep and see how much our brain waves change.
Non-REM sleep serves as the restore portion of the sleep cycle. For example, as we enter the beginning of non-REM sleep, the pituitary gland releases growth hormone to help repair our body tissues. Non-REM stages are also important to immune system regulation and ensuring our bodies are in top condition to fight off infections. Stage 3 is deep sleep and is believed to be critical for brain maintenance.
REM sleep (stage 4) helps our brains consolidate memories and process the information we’ve encountered throughout the day. This is likely why so many of our dreams fail to make sense or defy logic entirely—our brains are using this downtime during the night to help us remember details and make sense of the world!
Source: "The science of sleep: stages and cycles"
Go Deeper: To learn more about the architecture of sleep and circadian rhythms, check out this article from Harvard Medical School.
Aging Changes Our Sleep/Wake Cycle
As we age, structural and functional changes in the brain cause decreases in sleep hormones which makes falling asleep and/or staying asleep especially difficult the older we become. Sleep changes occur as we age regardless of our health status, making it a normal part of aging. In our research we found that sleep changes fall into categories: changes in sleep patterns, changes in circadian rhythm, and changes in neuroendocrine function.
The primary changes in sleep pattern that occur with age are in total sleep time and in sleep architecture (sleep cycle). For instance, this meta-analysis of 65 sleep studies (N=3577) in healthy subjects aged 5 to 102 years found that total sleep time, sleep efficiency, percentage of slow-wave (stage 3), percentage of REM sleep, and REM latency all significantly decreased with age. This study also found that sleep latency (sleep initiation or how long it takes to fall asleep), percentage of stage 1 sleep, percentage of stage 2 sleep, and wake after sleep onset significantly increased with age, all suggesting changes in sleep architecture not otherwise seen in younger adults, adolescents, and children. Why is this important: the sleep stages that seem to get compressed the most (stages 3 & 4) are also the most strategic for long-term health.
Changes in the circadian rhythm may help explain some of the changes to sleep patterns that have been documented in the literature. In fact, according to this study we found, a gradual breakdown in SCN function not only precipitates changes to circadian rhythm, but may even put individuals at risk for neurodegenerative conditions like Alzheimer’s disease. As we age we also experience what the research calls a “phase advance” in our internal clock pushing our sleep timing and structure forward. We get tired earlier in the evening and wake up earlier in the morning. The phase advance in our internal clock also affects the release of hormones tied to sleep like cortisol and melatonin. Other changes to our circadian rhythm with age include:
- Reduced amplitude of circadian waves—results in disrupted sleep
- Reduced ability to phase shift—results in older adults needing more time to recover lost sleep
- Decline in sleep homeostasis—results in less sleep pressure in older adults which may translate into more frequent awakenings during the night
Age-related changes to several hormones are also associated with poor sleep quality and quantity in older adults. Some of the major hormones that can affect sleep are:
Growth Hormone (GH) --In healthy, young adults, GH stimulates growth and cell reproduction; it also stimulates IGF-1 release from the liver, which helps regulate blood sugar as well as cell growth and development. In both sexes, alterations in anterior pituitary structure and function result in a decreased production of GH. Research suggests that GH and slow wave sleep impact each other. In healthy, younger adults, GH is secreted an hour into the sleep cycle and gradually slows as the night progresses. However, age-related declines in GH from adolescents to young adulthood and from young adulthood to middle- and older adulthood present a challenge to slow wave sleep. When GH levels are reduced or inhibited, there is an increase in corticotropin releasing hormone which limits slow wave sleep. As indicated above, less slow wave sleep = less restorative cleanse for your brain.
Cortisol --Cortisol secretion follows the dip-peak pattern of the circadian rhythm, with levels increasing in the morning and waning throughout the day. Age-related changes to the circadian rhythm result in a phase advance in cortisol levels, keeping nighttime cortisol levels higher in older adults than they are in younger adults. As such, some scientists speculate that higher nighttime cortisol results in more frequent awakenings and less time spent in slow wave sleep, further contributing to sleep disruption in older adults.
Melatonin -- Melatonin is produced by the pineal gland and helps regulate our sleep/wake cycle. Levels of circulating melatonin decrease in the morning and increase as the day progresses to get us ready for sleep. As we age, the pineal gland undergoes changes (e.g., calcification, reduction in size) that affect its structure and function. The result is a decrease in melatonin production and loss of a healthy sleep/wake cycle. In fact, according to this study, levels of nighttime melatonin are lower in older adults and result in disrupted sleep.
Sex Hormones -- Alterations in male and female sex hormones occur as a result of age. In men, testosterone decreases with age initiating a gradual change, referred to in the scientific literature as andropause. Older men also appear to lose their diurnal testosterone pattern (the dip-peak pattern that coincides with the circadian rhythm). As a result, older men are likely to experience fragmented sleep marked by frequent nighttime awakenings. In women, decreases in ovarian function results in a drop in estrogen and progesterone causing menopause. According to the research, the drop in female sex hormones is associated with trouble falling or staying asleep which causes fragmented sleep patterns in older women.
Go Deeper: For a summary of sleep changes that occur with age, check out this article.
Are Age-related Sleep Changes Dangerous?
We came away from our research with the impression that age-related sleep changes seem almost inevitable. The question is how can this impact our healthspan and what can we do about it.
Lack of sleep will certainly impact the quality of your life. But the effect is probably no different than in a young person who isn’t getting quality sleep. As we age, the amount of sleep we need remains more or less consistent after adolescence, ranging between 7-9 hours depending on the individual. So, while the reasons for sleep disruption often change throughout our lifetime, the effects of chronic sleep deprivation remain the same.
For instance, according to this article from Harvard Medical School, chronic sleep loss has been linked to a chronic disease (e.g., obesity, diabetes, heart disease, high blood pressure), mood disorders, cognitive decline, immune system dysfunction, and an increased risk of death. This 2012 study showed that our brains are bathed in cerebrospinal fluid during deep sleep in order to clear cellular debris like the amyloid plaques that cause Alzheimer’s disease; without deep sleep, our brains miss the chance for “clean up”, putting us at risk for cognitive decline and neurodegeneration. And remember, stage 3 sleep gets compressed as we age.
Additionally, this meta-analysis and review of 16 prospective studies (N=1,382,999) showed that when compared with normal sleep duration (7-8 hrs/night), short sleep duration (< 7 hrs/night) is associated with a 12% increase in mortality, an effect that remains consistent regardless of age, gender, or socioeconomic status.
Go Deeper: In this episode of his podcast, our favorite longevity guru, Dr. Peter Attia, sits down with neuroscientist and sleep expert Dr. Matthew Walker to talk about sleep architecture, why we sleep, the health risks of sleep deprivation, and even how poor sleep is linked to Alzheimer’s.
Using Sleep Hygiene to Your Benefit
Obstacles to good sleep change with age so our strategies have to change as well. Below are 9 fundamental sleep hygiene building blocks for older adults struggling to get a good night’s sleep:
- Turn off backlit devices (e.g., phones, tablets, laptops) at bedtime—Reading before bed is a great way to relax your mind, but backlit devices disrupt normal sleep/wake cycle. Switch to an e-reader that requires an alternative light source or read hard copies of your favorite book.
- Keep your bedroom dark and cool—When it comes to sleep, light is one of our worst enemies because it disrupts our internal clock. Our brains also respond to the ambient temperature to help regulate our core temperature, so a sleeping environment that is too light and too warm results in poor sleep quality. If your room is too light, room darkening shades or curtains can block out any excess light leaking into your bedroom. To keep your room cool, set your nighttime thermostat between 65-67 degrees or use a fan to cool down your room.
- Keep a consistent bedtime—This sleep hygiene staple is old hat, but keeping a consistent bedtime (as well as wake up time) can help regulate your internal clock.
- Early morning sunlight exposure—Nothing helps to synchronize your circadian clock better than exposing your retinal neurons to the wavelengths of the sun as it rises over the horizon. If you can, repeat the same as the sun sets.
- Diet matters—What you eat can have an effect on your ability to fall or stay asleep. While sugary foods, alcohol, and caffeine make sleeping more difficult, a light, low-carb bedtime snack, warm milk, or a cup of tea can help take the edge off any post-dinner hunger before bed.
- Move more—A small 2010 study (N=23) from Northwestern University found that performing endurance exercise 20-40 minutes per day at least 4 times per week can improve sleep quality in middle- and older adults.
- Say no to naps—It can be tempting to catch a nap during the day if you haven’t been sleeping well, but daytime napping can make it harder to sleep at night. If possible, avoid the temptation to nap, but if you do give in, keep it around 30 minutes and have your nap before 2pm.
- Limit the use of sleep aids—While pills like Ambien, Lunesta, and anxiolytics like Ativan and Xanax can be helpful if you’re dealing with insomnia, these prescription sleep aids have long-term side effects and also carry a risk of dependence. In particular, they tend to suppress stage 3 sleep. Consult your doctor if you’re considering using a sleep aid to catch up on your rest. They may be able to suggest a non-addictive substitute (e.g., diphenhydramine) or melatonin supplement to help take the edge off sleepless nights.
- Have a plan to get back to sleep—Frequent nighttime awakenings are common as we age and can be distressing especially if we’ve been practicing good sleep hygiene. Have a plan for what you can do to help ease yourself back to sleep that doesn’t involve bright lights or screens. One of our favorites is non-stimulating activity. For example, if you wake up and can’t get back to sleep, get out of bed, read a boring book for 20-30 minutes and try to get back to sleep. You can also try sleep meditations, deep breathing exercises, or progressive muscle relaxation.
For more practical tips on how to optimize the quality of your sleep, listen to Dr. Andrew Huberman’s podcast episode “Master Your Sleep and Be More Alert when Awake.”
Sleep is affected by age, but we aren’t powerless against it. What are some of your favorite techniques for a restful night’s sleep? Let us know: firstname.lastname@example.org
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