What’s something that you do daily that has such a profound effect on everything ranging from cognitive performance, physical health, mental well-being, and even your ability to drive a car? It’s so important that on average, humans spend about one third of their lives engaging in this activity. It is essential in many of our processes, yet over 70% of adults report not getting enough of it. So what’s this magical, elusive activity? Sleep.
Why Do We Sleep?
Even though we may think of sleep as a passive, relaxing event, one where everything “shuts down,” this isn’t exactly the case. You may not consciously be working, but your brain and body are.
During sleep, your brain clears itself of the waste products that it accumulates during the day. Throughout wakefulness, your brain is hard at work. As it engages in your everyday activities, waste products accumulate within the brain. This is normal, and isn’t a problem, IF you get enough good quality sleep. When you start to drift into dreamland, your brain’s garbage disposal starts to turn on. Just like when the trashmen come to your house to pick up your trash, the brain has a system that does something similar. The glymphatic system is the brain’s waste clearing pathway, and it is hard at work while you’re hard at rest (Eugene & Masiak, 2015). Proteins and waste products that accumulate in the brain’s interstitial space (the fluid that fills the space in your brain) while you’re awake can lead to neurodegenerative diseases such as Alzheimer’s disease or Dementia if they are not disposed of properly (Xie et al., 2013). The interstitial fluid in your brain increases by about 60% while we’re asleep, which allows Cerebrospinal Fluid (CSF) to be pulsated through the brain around every 20 seconds. CFS clears the brain of waste products while simultaneously re oxygenating the brain (Reddy & van der Werf, 2020). Think of this like your brain going through its own car wash every night that you get quality sleep..it comes out the next morning looking all shiny and clean!
While your brain is going through it’s nightly carwash, it’s also hard at work engaging in other processes. Remember how in college you would always (or still do…) pull an all-nighter to cram for an exam the next day, only to forget everything you “learned” overnight once you sat down to take the test (not me speaking from experience…)? There’s an actual physiological reason that happened! Sleep is crucial for memory consolidation. During the stages of sleep called Non-Rapid Eye Movement (NREM), we experience Sleep Spindles, which is a pattern of brain waves that occur during sleep. Studies have shown that after learning, there is increased sleep spindle activity both during daytime naps and overnight sleeping (Ulrich, 2016). They have also found a linear correlation between sleep spindle activity and recall performance (Ulrich, 2016). Even more interestingly, neurodegenerative diseases that are associated with loss of memory are also associated with reduced sleep spindle activity (Lu & Göder, 2012). Although science is still trying to figure out how exactly sleep spindles work to help with memory consolidation, we can rest assured (pun intended) that higher quality and quantity sleep can be beneficial to learning and memory.
Sleep Deficiency and Cognition
As you saw above, lack of good quality sleep may impact both the susceptibility of developing neurodegenerative diseases, and the ability to optimize memory. But regular sleep disturbances that are all too common for the majority of us may be getting in the way of our ability to perform at our cognitive peak.
Several cognitive functions rely on good quality sleep for their proper operation. Mood, emotional regulation, stress coping, attentional control (van Someren et al., 2015), creativity, innovation (Killgore, 2010), social behavior (Dorrian et al., 2019), motivation (Odle-Dusseau et al., 2010), cognitive flexibility (Whitney et al., 2017), logical reasoning, decision making, and problem solving (Baert et al., 2015) are all cognitive domains that have been shown to be impacted by sleep disturbances. Researchers have found that in workers who averaged less than 7-8 hours of sleep per night, there were significantly higher productivity losses when compared to individuals who got sufficient sleep (Hafner et al., 2017). These productivity losses were equivalent to almost 8 days of lost work performance per year! That’s a week and a half of vacation time you could have spent on a beach somewhere… And what’s worse? These performance losses translate into loss of wages as well. Researchers have found that a slight 1 hour/week increase in average sleep time can result in a 4.5% increase in wages over the long-term (Hafner et al., 2017). A raise, AND extra vacation time? Count me in.
Sleep disturbances are affecting our productivity in the workforce, but also in the younger generations who are broadening their knowledge and skill set in school. Insufficient sleep has been correlated with poor grades in academics (Fernandez-Medina et al., 2020). As we’ve mentioned before, good quality sleep is necessary for memory formation, but also for motivation, attention, and self-efficacy, all of which are important for academic achievement (Fernandez-Medina et al., 2020). According to a National Sleep Foundation Study, more than 87% of high school aged students are not getting the recommended hours of sleep (Hafner et al., 2017). The future of our nation is chronically sleep deprived…this sounds promising.
Not only are these cognitive processes directly impacted by lack of quality sleep, but the cognitive killers that I’ve discussed on previous blogs can also be exacerbated by sleep disturbances. Short sleep can disrupt the expression of genes that are implicated in inflammation, and has been linked to abnormal glucose metabolism and an increased risk of insulin resistance and type 2 diabetes (van Someren et al., 2015). Have you ever had a rough night’s sleep, and then spent the next day binging on all sorts of highly processed (but equally delicious) foods? That’s unfortunately, normal. Lack of good quality sleep can dysregulate our control of appetite by increasing hormones that make us feel hungry and decreasing hormones that tell us we’re satiated (van Someren et al., 2015). This leads to an increased likelihood of overconsuming foods, especially by way of snacking. And no, when we’re sleep deprived we don’t tend to overeat salads and apples, but instead binge on foods that light up our reward pathways such as hyperpalatable foods (think: candy, potato chips, french fries and cheeseburgers). This can lead to an increased risk of weight gain, which as we know, can drive both metabolic dysregulation and inflammation. Definitely not a good sign for our brains!
Diet and Shut Eye
Of course if it’s a blog post I’m writing, diet has to fit into this equation somehow. Diet and sleep have an intricate bi-directional relationship. Just as lack of sleep can regulate our nutritional habits, our dietary patterns can impact our ability to have high quality sleep. If you’re like many adults who have trouble getting good quality shut eye, the good news is that looking at our overall diet may provide some clues as to how we can begin getting better sleep.
Some diets that are commonly promoted as “healthy,” such as the Mediterranean Diet (Muscogiuri et al., 2020), and the DASH diet (Rostami et al., 2019) have been shown to have a positive effect on sleep quality and quantity in the studied populations. In fact, one study has found a significant correlation between adherence to the Mediterranean Diet (MD) and sleep quality. Godos et al., (2019) found that for every one-point increase on Mediterranean Diet score, individuals were 10% more likely to have better sleep quality. Both the MD and the DASH diet are high in nutrient-dense foods such as fruits and vegetables, fish, nuts and seeds, and are low in lesser-nutritious foods such as refined grains, red or processed meats, and sugar-sweetened beverages. So what do these foods have to do with sleep?
Firstly, neuroinflammation, inflammation in general, and oxidative stress may contribute to poor sleep quality (Godos et al., 2019, Kanagasabai & Ardern, 2015). Many of the components of the MD and DASH diets are anti-inflammatory in nature, which may reduce the risk of inflammation and oxidative stress and therefore improve one’s probability of higher sleep quality (Fernandez-Medina et al., 2020).
These diets are also high in nutrients that our bodies need to regulate sleep. Tryptophan is an amino acid that serves as the precursor for melatonin, those pills that you take when you have trouble sleeping. Kidding…kinda. Melatonin is a naturally produced hormone in the body that regulates our sleep-wake cycle. For our body to be able to synthesize this hormone properly, it needs adequate levels of tryptophan, and the MD is high in tryptophan-containing foods (Fernandez-Medina et al., 2020). Tryptophan-rich foods include: lean poultry (turkey and chicken), fish (salmon, sardines, oysters), dairy products (milk and cheese), and nuts and seeds.
Both the MD and the DASH diets are commonly full of foods that are considered “low” on the glycemic index (GI) scale. Low GI foods are those that, once eaten, won’t spike your blood sugar and insulin levels. High GI diets (diets with foods that easily spike blood sugar and insulin levels) have been associated with increased insomnia, particularly when consuming high intakes of added sugars, starches, and refined grains (Gangswich et al., 2020). Conversely, foods that are high in fiber and whole fruits are associated with a decreased risk of insomnia (Gangswich et al., 2020). The MD and DASH diets are high in both fiber, and whole fruit products.
Finally, higher levels of omega-3’s in the body is correlated with significantly improved sleep wellness (Zhao et al., 2020). In one study, participants in the omega-3 supplementation group had an average of 58 minutes increase in sleep duration, as well as fewer instances of waking throughout the night when compared to the control group (Montgomery et al., 2014). The MD particularly is high in foods that contain omega-3 fatty acids including Salmon, Oysters, Sardines, and other types of fatty fish.
Besides these two diets, there are a few other nutritional components that need to be touched on as it relates to sleep. Here are two specifically that need to be highlighted (readers beware..).
- Caffeine: OK hear me out..I’m a coffee fan too, but in moderation and at appropriate times. It doesn’t take me having to tell you that caffeine consumption, especially too late in the day, messes with your sleep. Too much caffeine can cause a decrease in sleep time and sleep quality, and it will cause you to take longer to fall asleep once you get into bed (Zhao et al., 2020). Listen, I’m not a crazy person, so I’m not going to tell you to give up coffee. However, when drinking caffeine, try to do so before 1pm, and limit to only 2-3 cups a day. That’s a reasonable ask, right?
- Alcohol: although a night of heavy drinking may help you to “pass out quickly” (not me talking from experience..again…), it doesn’t result in quality sleep. Alcohol consumption prior to bed can reduce REM sleep and cause sleep disruptions (Park et al., 2015). One study found that low amounts of alcohol, characterized by fewer than 2 drinks per day for men, 1 drink per day for women, decreased sleep quality by 9.3%. Moderate amounts of alcohol, 2 drinks per day for men, 1 drink per day for women, decreased sleep quality by 24%. And high amounts of alcohol, greater than 2 drinks per day for men, and 1 drink per day for women, decreased sleep quality by 39% (Pietila et al., 2018). Again, I’m not going to suggest you give up drinking, but do so in a mindful way as you now know the impact that it has on your sleep quality.
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Instead of Counting Sheep You Can…
Obviously, sleep is important. Not only to be able to function optimally the next day, but to reduce your risk of several health implications like MetS, chronic inflammation, or even neurodegenerative diseases. If you’re part of the 70% of adults who don’t get enough sleep, try out some of these tips.
- Add in a few servings of fatty fish weekly: as you saw above, Omega-3 fatty acids are correlated with better sleep quality. Try adding in a serving or two of wild caught salmon, sardines, cod, oysters, or mackerel into your regular meal schedule.
- Increase intake of tryptophan containing foods: tryptophan is needed for the body to form melatonin-the hormone that helps you sleep. Foods high in tryptophan include lean poultry, dairy products, fish, nuts, and seeds.
- Increase your intake of fiber: fiber has been shown to decrease your risk of insomnia. Fiber is best found in its whole plant food version. Foods rich in fiber include vegetables, whole grains, fruits, nuts, and seeds.
- Limit high GI foods: these include added sugars, starches, and refined grains, as these are correlated with increased risk of insomnia. Try and limit the consumption of these foods especially as it gets closer to bed time.
- Be careful with caffeine and alcohol consumption: as you saw above, these can be damaging to a good night’s sleep. Try to have a “cut-off” from caffeine before 1pm, and when drinking at night do so in lesser amounts most of the time (and if you really have trouble sleeping, try completely cutting it out for a night..or three..and see how you feel!).
- Regulate your routine: give yourself a “wind-down” routine that you engage in nightly that helps your brain to prepare for sleep. This can include some gentle yoga, reading, meditation, or journaling. Anything that doesn’t include looking at screens!!!
If you want a magic pill to take that will: improve your quality of life, sharpen your memory, make you less susceptible to diseases such as diabetes, metabolic syndrome, and Alzheimer’s, increase your energy, and help you to perform better in your job…save your money try getting some regular, quality shut eye nightly instead.
References
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Dorrian, J., Centofanti, S., Smith, A., & McDermott, K. D. (2019). Self-regulation and social behavior during sleep deprivation. Sleep Deprivation and Cognition, 73–110. https://doi.org/10.1016/bs.pbr.2019.03.010
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