As a follow up to our recently published The Gut-Sleep Connection series, we’ll now explore What Happens During Sleep and When We’re Sleep Deprived.
What Happens During Sleep
After waking from a bizarre dream, we sometimes perceive sleep as chaotic and unstructured. The opposite is actually true. Sleep is highly controlled and predictable. Two different types of sleep occur through a total of five stages that repeat every 90 minutes for about five cycles over a full night’s sleep. It is just that precise. The two types of sleep are non-rapid eye movement (NREM) and rapid eye moment (REM).
Non-rapid eye movement (NREM) sleep has four stages that take us from light sleep to deep sleep, indicated by slow brain waves, lower pulse and dropped blood pressure. We spend about 75% of our sleep time in this state. NREM plays a role in transferring new information, skills or memories to long-term storage. A part of that process is weeding out unnecessary neural connections so that we remember what we need to and forget what we don’t (McCarley 2007). It’s during the deepest stages of NREM that the body boosts immunity, balances metabolism, regulates blood pressure and repairs muscles/tissues.
Rapid eye moment (REM) sleep, commonly known as the dreaming stage, takes the information transferred during NREM and integrates it with all other existing memories. REM helps make sense of what we learned that day and places it in the context of what we already know. REM is also a time when we have an emotional reset and find resolution with the day’s experiences. This overnight therapy session is what makes it possible to wake level-headed, accurately read social cues and navigate through life’s challenges (Kahn, Sheppes & Sadeh 2013; Nishida et al. 2009). The reason why people experience the bizarre scenarios that can arise in dreams during this stage is because rational thought is deactivated and anything is possible! This is also how sleep inspires creativity and assists us with problem-solving, by helping us get out of our own conscious, sometimes narrow-minded way.
All types and stages of sleep have specific functions benefiting health and well-being. The timing is just as important as the action of sleep. Research demonstrates that the early hours of sleep are dominated by NREM, while the later hours, especially the last 2 hours of an 8-hour sleep night, are dominated by REM (Walker 2017). Sleep stages are experienced every 90 minutes; the ratios simply change. This makes getting a full night’s sleep, aligned with circadian rhythms and without sleep aids, critical to reaping the health benefits of sleep.
What Happens When We’re Sleep Deprived?
A loss of sleep, defined as sleeping less than 7 hours a day, impairs well-being and results in a suboptimal physical and psychological state. Even over a mere 10 days, the brain and body are deeply compromised. (Just imagine what years of insufficient sleep may do.) Sleep deprivation affects our ability to concentrate, learn and remember (Havekes, Vecsey & Abel 2012). It also influences our emotional state by increasing reactivity, mood swings, aggression and hypersensitivities, while creating a fear-based mindset. A lack of sleep literally makes us more animalistic by switching our brain activity from the cortex to primitive brain regions. Forget about problem-solving, brainstorming, insights or creativity. Those are out of reach.
Sleep deprivation also takes its toll on the body. Without enough sleep or enough quality sleep to nurture all sleep stages, renewal, detoxification and enhancement processes are never fully completed. Over time, this leads to compromised immunity, unmanaged inflammation and the onset of diseases and conditions like heart disease, diabetes, obesity, cancer, depression, anxiety, Alzheimer’s, autoimmune illnesses and digestive disorders (Ali et al. 2013; Covassin & Singh 2016; Hsaio et al. 2015; McEwen & Karatsoreos 2015; Mullington et al. 2009; Nagai, Hoshide & Kario 2010).
A major pathway that links sleep to illness is the way circadian rhythms regulate immunity and the corresponding hypothalamic-pituitary-adrenal (HPA) stress axis (Buckley & Schatzberg 2005; Hirotsu, Tufik & Anderson 2015). When we are sleep deprived, the HPA stress axis is activated, resulting in hormone shifts: Cortisol increases, and levels of growth hormone decrease (Besedovky, Lange & Born 2012; Kim, Jeong & Hong 2015; Rea, Dinan & Cryan 2016). This compromises immunity, affecting our ability to manage inflammation and fight off infection.
As sleep deprivation keeps the stress axis on high alert, the effects alter metabolic activity, particularly insulin regulation, thereby further suppressing the immune system (Tsai et al. 2018). In conjuction with the hyperactive stress response, the sympathetic nervous system (SNS) remains in a fight-or-flight status. When the SNS stays in an “on” position without balance from the parasympathetic nervous system (PNS), the result is suppression of anti-inflammatory processes and higher susceptibility to disease.
Fortunately, there is good news: We are taken out of the SNS during NREM sleep, and the release of stress chemicals, specifically norepinephrine from the SNS, shuts off during REM sleep (Walker 2017). Sleep helps us manage stress, resolve emotions and wake with a clear head. Since inflammatory and psychological pathways are shared in the body, this in turn affects immunity (Sternberg 2001). But it doesn’t stop there. The sleep-immunity connection is also intricately linked to the gut.
In our next part, we will look deeper into HOW GUT HEALTH PLAYS A PART and SLEEP MANAGES APPETITE AND METABOLISM.
References from IDEA Fitness Journal March-April 2020 “The Gut-Sleep Connection” by Teri Mosey, PhD