Rest is a vital part of our immune system, but unfortunately, it’s often overlooked. Many of us opt for spending late nights working or binge-watching TV instead of sleeping. While it’s tempting to catch up on Disney classics before bed, Sleeping Beauty may have had the answer we’ve been looking for all along. Quality sleep positively impacts our overall health and wellbeing. If you’re wanting my late-night TV recommendation for good health, I’d recommend the back of your eyelids.
Sleep disorders are a common problem in Australia, with over 1.2 million Australians estimated to experience sleeping problems[1]. Sleep is an essential element of living and keeps us happy, healthy and sniffle-free, so let’s explore the link between sleep and the immune system.
What happens when we sleep?
Sleep is essential for our bodies, as it enables us to filter and process what we’ve done throughout the day. Sleep impacts our alertness, tiredness and cognitive function[2].
The sleep/wake cycle, known as our circadian rhythm, is part of our nervous system and is controlled by the hypothalamus. When it’s dark at night, our eyes send a signal to the hypothalamus to say that it’s time to feel tired. Our brain then sends messages to release melatonin, which increases tiredness. When we sleep, the body repairs and restores our muscles and organs, and enables our immune system and metabolism to reach a balance, known as homeostasis, which is why sleep and recovery are so closely linked.
Why we sleep
There’s a communication network between the immune system and our nervous system. Neurons and immune cells share intercellular signals, such as hormones, cytokines, neurotransmitters and modulators[2]. Our immune system is regulated by our nervous system directly via hormones and indirectly through blood flow, blood pressure and lymphatic flow[3]. Conversely, our immune cells traffic to all the cells in the body and come into close contact with nerve endings.
When we’re asleep, the body enhances the consolidation of both our neurobehavioral and immunological memories[2]. These memories form the basis of the body’s memory, creating its’ ability to adapt to future stressors[2]. Without sleep, the body is deprived of this memory formation, and may not be able to adapt as adequately with reoccurring stressors.
Why does sleep help when you’re sick?
Sleep helps when you’re sick because it’s when the body responds to ‘danger signals’ that have occurred throughout the day, including physical activity and cell injury[3]. At the beginning of the sleep cycle, the body releases pro-inflammatory cytokines. In turn, these pro-inflammatory cytokines support our immune responses. If we’re sleep-deprived, the body still exerts an inflammatory response, leaving us feeling weak and fatigued. These pro-inflammatory mediators rise when we don’t get enough sleep, increasing our overall bodily inflammation[3].
While we’re asleep, the body also releases immunoregulatory cytokines, such as interleukin (IL)-1, impacting our immune system.
How does sleep fight off infection?
Sleep helps fight off infection because it improves the ability of some of the body’s immune cells, known as T cells, to attach to virus-infected cells and kill them. This is partly because adrenalin and prostaglandin levels dip while the body is asleep, and these two hormones can prevent T cells from working properly to kill infected cells[4].
When we don’t get enough sleep
Loss of sleep can infer a negative impact on our immune system and suppress our immune response. While excessive sleep won’t stop you from getting a cold, sleep deprivation makes us more susceptible[3]. Sleep deprivation decreases our production of lymphocytes and natural killer cells, which plays an important role in our immune system[3].
Sleep deprivation can increase our stress hormone cortisol, suppressing immune system function and reducing our ability to fight inflammation[2].
Why do I feel sick at night but not during the day?
It’s common to experience feeling sick at night because of your body’s circadian rhythms. This helps regulate both sleep and the immune system, and as a result, means that the immune system is most active during sleep. When the immune system kicks in, it releases a variety of chemicals to help fight infection, some of which also induce inflammation. This means that while your body is busy fighting the infection, some of your symptoms (such as fever or a sore throat) may be temporarily exacerbated by the inflammation. The immune system is least active during the afternoon or early evening, which is when you may feel a bit better[5].
When we fall sick
When we do get a cold, our demand for sleep increases[6]. It’s so important to listen to this signal and allow your body to sleep to recover as quickly as possible from illness.
We encourage you to prioritise your sleep. We recommend that you create a beautiful night-time routine to help you drift off peacefully and support your immune system.
References:
- Hechtman, Leah 2012, Clinical Naturopathic Medicine, Elselvier, Sydney.
- Besedovsky, Luciana, et al., 2011, ‘Sleep and immune function’, European Journal of Psychology, vol. 463 no. 1 pp. 121-137
- Asif, Nayyab, et al., 2017, ‘Human immune system during sleep, American Journal of Clinical and Experimental Immunology, vol. 6 no. 6 pp. 92-96
- Stoyan Dimitrov, Tanja Lange, Cécile Gouttefangeas, Anja T.R. Jensen, Michael Szczepanski, Jannik Lehnnolz, Surjo Soekadar, Hans-Georg Rammensee, Jan Born, Luciana Besedovsky. Gαs-coupled receptor signaling and sleep regulate integrin activation of human antigen-specific T cells. The Journal of Experimental Medicine, 2019; jem.20181169 DOI: 10.1084/jem.20181169
- Smolensky MH, Reinberg A, Labrecque G. Twenty-four hour pattern in symptom intensity of viral and allergic rhinitis: treatment implications. J Allergy Clin Immunol. 1995;95(5 Pt 2):1084-1096. doi:10.1016/s0091-6749(95)70212-1
- Benington JH, et al., 1995, ‘Restoration of brain energy metabolism as the function of sleep’, Process in Neurobiology, vol. 45 no. 4 pp. 347-360
