Many of us are stressed in our everyday lives and while we know stress can take a toll on our bodies, it is surprising how much stress can affect our ability to fight off disease. This week we focus on how stress can affect our immunity and ultimately increase our susceptibility to disease. While much research has been conducted on the topic, it is quite surprising that definitive answers have yet to be found. We discuss how stress can affect our immune system thus leading to susceptibility to developing the common cold, as well as how other diseases may or may not be easier to develop because of stress.
In Chapter 8 of Sapolsky’s book: Why Zebras Don’t Get Ulcers (2004) we are given an introduction to how our immune system works. We know through our middle school science courses that our immune system is supposed to attack things that are foreign to our body while ignoring the cells our bodies produce. While this sounds easy, our immune system is actually quite complicated. From this chapter we learn that are immune defenses are lead by cells that circulate throughout our bodies called lymphocytes and monocytes (white blood cells). Specifically, there are T and B cells that work together in different ways to fight off infectious diseases. In some cases, T cells especially will fail to extinguish foreign invaders from our own healthy cells leading to autoimmune diseases or they may fight against objects that are ingested or touched such as allergens. From this chapter, we begin to understand the details of how our immune system works, but now we want to focus on how stress can affect our immune system and lead to the potential development of diseases. When an individual is stressed they will fail to form new lymphocytes and the lymphocytes that are currently circulating in their bodies will have a short life. They will be unable to create new antibodies when they get in contact with something infectious and there will no longer be communication among lymphocytes causing havoc, all caused by the increase of glucocorticoids in our system. So while we know how stress can affect the immune response, questions that spark our interests currently are whether or not stress makes us more susceptible to developing illnesses such as cancer, the common cold, and depression.
There has been a great number of studies that have sought to answer the question proposed above. One such study was conducted by Cohen and Colleagues (2012) to determine how chronic stress may make an individual susceptible to developing the common cold. They answered this question in two separate studies. The first study assessed stressful life events and glucocorticoid receptor resistance (GCR). GCR refers to the lack of sensitivity immune cells have to glucocorticoid hormones that are designed to stop inflammatory response. The results of their first study found that stressed individuals had a greater risk for developing a common cold. This is caused by the interference by GCR with the HPA down-regulation of pro-inflammatory cytokine is released in response to an infectious agent. Study 2 sought to use the measurement of GCR as a predictor for how much local pro-inflammatory cytokine was produced in response to an infection. Their results showed that greater GCR predicted production of more local pro-inflammatory cytokines in individuals with the common cold. This data suggests that dealing with prolonged stress can result in GCR which interferes with the regulation of inflammation which makes individuals susceptible to developing the common cold (Cohen et al., 2012). Additionally, a review paper by Hodes and colleagues (2015) discuss how elevated pro-inflammatory cytokines circulating throughout our bodies that increase leukocytes can contribute to development and maintenance of depression (Hodes, Kana, Menard, Merad, and Russo, 2015).
Lastly, there is a false concept that increased stress can lead to the development of cancer. While there are many animal studies that show stress can, in fact, increase tumor sizes, there are many studies that find no association between stress and cancer. One such study was conducted by Shoemaker and colleagues (2016) that sought to understand whether the frequency of stress and adverse life events had anything to do with the risk of developing breast cancer. This study is unique in that they used a cohort of 106,000 women from the United Kingdom. From these women, they gathered breast cancer diagnoses every 3 years as well as any stressful or adverse life events. Their results showed there to be no association of breast cancer risk with the overall frequency of stress. To many, these results may seem surprising which is understandable. In his chapter, Sapolsky explains many ways stress can attribute to tumor growth and development and he discusses why some studies that do show associations between stressful life events and cancer could be false because of their retrospective aspect. However, even in the discussion, Shoemaker and colleagues (2016) do not provide a concrete reason for their results (Shoemaker et al., 2016).
Together these articles and book chapter help us understand how stress can affect our bodies in more ways than one. One question I had that was answered during our discussion in class was how the stress we put our bodies through while working out may have a negative physiological outcome. However, Julie said it best that this only happens when we overdo our workouts. We have to find a balance between getting a good workout in that actually increases our immune system helping us fight off the common cold, to not pushing ourselves over our limits during a workout where we feel like our bodies are fighting against us.
Cohen, S., Janicki-Deverts, D., Doyle, W.J., Miller, G.E., Frank, E., Rabin, B.S., & Turner, R.B. (2012) Chronic stress, glucocorticoid receptor resistance inflammation, and disease risk. PNAS, 109(16), 5995-5999.
Hodes, G.E., Kana, V., Menard, C., Merad, M., & Russo, S.J. (2015). Neuroimmune mechanisms of depression. Nature Neuroscience, 18(10), 1386-1393.
Sapolsky, R.M. (2004) Why zebras don’t get ulcers: A guide to stress, stress related diseases, and coping. New York: W.H. Freeman.
Shoemaker, M.J., Jones, M.E., Wright, L.B., Griffin, J., McFadden, E., Ashworth, A., & Swerdlow, A.J. (2016). Psychological stress, adverse lfie events and breast cancer incidence: a cohort investigation in 106,000 women in the United Kingdom. Breast Cancer Research, 18(72).