Sleep: Your immune system's best friend

By Meryl Ong

For more articles on healthy habits and lifestyle medicine, please visit Meryl's blog: The Mindful Hustle


With the exam season fast approaching, many of us have succumbed to the temptation of pulling late-night study sessions. After all, sacrificing a few hours of sleep in exchange for revision will surely pay off, right? While it is true that night revision can be more effective for some, a problem may arise if this habit translates into a persistent issue of sleep deprivation.

In this article, I seek to explain the scientific links between sleep and immune function, highlight the consequences of chronic sleep deprivation and finally, offer some fun & simple suggestions to help you develop better sleep habits. (Do note that the scientific concepts referred to have been simplified for easier understanding.) Here we go!


The Link Between Sleep and Immunity

As the global community endures in our battle against COVID-19, our heightened understanding of the invasion of pathogens into our bodies has helped us to recognise the importance of maintaining a strong immune system.


Sleep is a critical period for the strengthening of our immune functions. This is because during early stages of rest, a rise in hormones such as the pituitary growth hormone (GH), prolactin and melatonin occurs in our blood. This sends a pro-inflammatory signal, which stimulates our immune system. This is followed by an activation of immune cells in our bodies, which leads to a rapid increase in pro-inflammatory cytokines - small proteins responsible for communication between cells, regulating our body’s response to infections and inflammations. Essentially, they provide immune defence in the body while we are asleep, recognising and eliminating cells with foreign antigens (structures which indicate that it is non-self). This phenomenon occurs due to the build up of ‘danger signals’ during the day, which come into effect while we are resting at night.


Besides the effects of a rise in hormones and danger signals, our circadian rhythm also has a role to play in controlling various processes involved in an immune response. The Circadian Locomotor Output Cycles Kaput aka CLOCK gene is a key component of our internal circadian clock, and its activity enhances immune activation in the body during the night. Moreover, it has been found that lymphocytes (a type of white blood cell) builds up in the lymph nodes during sleep. All this is possible due to the coordination between the circadian and immune rhythms, where nocturnal sleep is associated with a rise in inflammatory activity.


Finally, in the same way sleep promotes memory consolidation, this idea can be applied to the formation of immunological memory, which intensifies during sleep. Should these processes occur during waking hours of the day, it can result in fatigue, immobility and pain - which would render us unable to cope with the mental, physical and environmental elements we face on a daily basis.


A noteworthy fact:

You may be surprised to learn that a lack of sleep can result in lowered efficacy of flu vaccinations, which builds upon the concept that inadequate sleep is linked to impaired immune function. As such, if you would like to ‘milk’ the benefits of receiving a flu jab, research suggests that treating your body right with a sufficient amount of sleep is the way to go.


How much sleep do we actually need?

Studies have revealed that the widely recommended 8 hours of sleep is not necessarily the optimal duration for everyone. Instead, the number of hours of sleep someone needs is dependent on a range of factors, including genetics, sleep quality and age. The overall trend is that the older someone gets, the less sleep he or she requires per night. Teenagers aged between 14 to 17 years should clock in around 8-10 hours, whereas adults need approximately 7 to 9 hours. This, of course, only serves as a general rule of thumb.


On this note, relying on physical cues is the easiest way to determine if we have obtained sufficient sleep. These include feeling refreshed and energised upon getting up in the morning, the ability to last the day without feeling sleepy, as well as having the mental energy to focus on tasks. That said, if you find yourself nodding off to sleep during lessons, chances are you’re not obtaining sufficient rest at night!


Repercussions of Inadequate Sleep

Now that we have established the scientific links between sleep and immunity, let’s shift our focus to understand the other consequences of sleep deprivation.


Interestingly, many studies on the effects of sleep deprivation have compared the performance of sleep-deprived individuals to people under the influence of alcohol. In one such study, people facing a lack of sleep were placed in a driving simulator and given a hand-eye coordination task. Results reveal that they performed as poorly or even worse in the activity compared to those who had consumed alcohol. Therefore, hand-eye coordination can worsen with insufficient sleep.


Apart from a deterioration of hand-eye coordination and weaker immunity, a lack of sleep can also result in:

· Poorer memory

· Increased sensitivity to pain

· Development of depression

· Impaired ability to make wise decisions

· Increased tendency to overeat

· Greater risk of developing chronic, non-communicable diseases such as hypertension, diabetes, heart disease and obesity


Another interesting point to note is that nights of inadequate rest can result in an accumulation of ‘sleep debt’. Similar to the idea of paying off your loans, your body will eventually need to make up for missed sleep. A 2016 study found that our bodies require four whole days to recover from just an hour of lost sleep. As such, a growing sleep deficit may become increasingly difficult to overcome, and symptoms associated with sleep deprivation may persist for prolonged periods of time.



Building Better Sleep Habits

Making simple changes to your routine can lead to significant improvements in your sleep quality and duration. Here is a list of ideas reviewed by health professionals to encourage you to make a start:


· Adhere to a sleep schedule - try your best to fall asleep and awake at the same time every day. Personally, keeping tabs on how I spend the last few hours of my day by means of a timetable has helped me to work towards achieving this goal. Additionally, I find the ‘bedtime reminder’ feature on my mobile phone a useful way to prompt myself to wind down, just in time for bed.

· Avoid drinking caffeine after lunch

· Avoid drinking alcohol before bed

· Craft a personalised bedtime routine (this can entail reading a book before bed, performing light stretches, taking a hot shower, listening to soothing music etc.)

· Where possible, steer away from the usage of computers, smartphones or the television before bed

· Exercise regularly, preferably 5 hours or more before your bedtime. This is because adrenaline levels, heart rate as well as body temperature remain high for some time after exercise, which may hinder your ability to fall asleep!

· Should you wish to nap during the day, try to limit its duration to 30 minutes or less. This will prevent the disruption of your sleep schedule. · If you’re a tea lover, you can find a list of yummy bedtime herbal teas here!

· Most importantly, if you have been experiencing regular sleep problems, it will be best to seek professional help from a medical doctor


I hope this has inspired you to catch more Zzzzzs!


References:

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3256323/

2. https://pubmed.ncbi.nlm.nih.gov/20398008/

3. https://www.webmd.com/sleep-disorders/sleep-requirements

4. https://www.psychologytoday.com/us/blog/refire-don-t-retire/201609/how-much-sleep-do-you-really-need

5. https://www.webmd.com/sleep-disorders/features/immune-system-lack-of-sleep

6. https://ghr.nlm.nih.gov/gene/CLOCK

7. https://www.nhs.uk/live-well/sleep-and-tiredness/how-to-get-to-sleep/

8. https://www.webmd.com/sleep-disorders/features/can-exercising-at-night-hurt-your-sleep

9. https://pubmed.ncbi.nlm.nih.gov/27775095/