I Am Tired...Achoo! Is That A Cold?!
- The Little Physio
- May 10, 2019
- 3 min read
Sleep has many restorative physiological functions one of which ties in with the immune system. We can be aware of an impending cold when we have been sleep deprived or have experienced some sleep debt, for whatever reason. Maybe you can remember a cold when you were studying for exams, when you were working late shifts or had a great weekend socialising to the wee hours of the morning.
This blog post will explore the relationship between sleep and the immune system, and why we can get sick when we are in sleep debt.
The immune system
Our immune system is a highly complex army of cell and factors with the ability to detect and eliminate the right enemy in the body. The immune system can be separated into the innate and the adaptive immune system. Each arm of the immune system has a different purpose.
The innate system is the first line of defence in the presence of a pathogen or ‘intruder’. If the first line of defence fails to eliminate the pathogen then the adaptive arm of the immune response will also go to war. The adaptive immune system is developed to be able to use the right type of cells for a specific pathogen. For a quick summary of the complexity of the immune system, check out this video.
How does sleep influence the immune system?
When it comes to sleep, there are multiple studies describing the impact of sleep on the immune system, some of which are reviewed by Irwin (2016 and 2017).
Sleep can influence the immune system by affecting the hypothalamic pituitary axis (HPA) and the sympathetic nervous system (SNS). These systems are also activated when we are stressed; so if there is a combination of sleep deprivation and stressful events this can diminish optimal immune system function.
Through the HPA and SNS, during sleep there is a normal rise and fall of neurotransmitters and hormones. For example, norepinephrine and cortisol drop during sleep whilst hormones related to grown and restoration increase, such as prolactin, growth hormone and melatonin.
During sleep, there is an increase in development/differentiation in a T cell subtype belonging to the adaptive immune system and an increase in the cytokine interferon-gamma (IFNy). This T cell subtype and immune cytokine plays a role in the defence against viruses, such as the common cold. Meanwhile, there is a decrease in the expression of interleukin 10, a factor which suppresses immune response activity. Thus, during sleep, the body is primed to fight viral infections.
How does sleep deprivation affect body?
Lowered immune response
Sleep deprivation can be defined as loss of a whole or part of a nights sleep, or fragmented sleep.
With chronic sleep deprivation there is the HPA and SNS are activated. This initially leads to inhibition of the cortisol/glucocorticoid response, thus there is an acute immunosuppressive effect. With chronic SNS activation via sleep deprivation, anti-viral activity is decreased but there is an increase in an inflammatory profile, thus leading to chronic inflammation with a compromised immune response. Furthermore, an effective immune response to vaccinations is impaired with sleep deprivation and this lack of response persists six months later with booster shots.
When we look at the details we see a shift of T cells to a subtype more capable of attacking bacteria as opposed to viruses and a shift in cytokine production to a profile promoting immunosuppression.
In a sleep deprived body, your immune system is less capable of ramping up an appropriate immune response to things like the common cold. Thus, we are susceptible to getting sick at times when we are tired.
Chronic diseases
Cardiovascular disease is considered an inflammatory disease. Sleep issues can lead to chronic inflammation and via this mechanism promote cardiovascular disease. In the cases of individuals with more than one year history of insomnia, less than 5 hours of sleep or more than 7 hours of sleep, increased risk for high blood pressure, and increased morbidity and mortality for coronary heart disease and stroke.
With sleep deprivation there is also a decrease in the natural killler cell population. This is a cell type with crucial roles in recognising and eliminating ‘old’ cells as well as tumours/cancerous cells.
Sleep well
We have much to be grateful for when it comes to our immune system. Without an immune system we would be at prey to pathogens surrounding us daily. Optimal function of the immune system is tied closely with good quality and consistent sleep of 7-8 hours duration. Good sleep regulates the flux of immunoprotecting factors to ward off infections and chronic diseases. When your mum or dad says, go to sleep when you are busy studying or working, they are within very good reason. So, sleep well for your body and long term health.
Resources for further information
Summary of immune system
Irwin 2016 - Why Sleep Is Important for Health: A Psychoneuroimmunology Perspective
Irwin 2017 - Sleep Health: Reciprocal Regulation of Sleep and Innate Immunity
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5143488/
Comments