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Psychophysiology is the scientific study of the interaction between the mind and the body. The impact of psychological stress and mental activity can have an adverse effect on the body, which in turn can lead to disease (Lovallo, 2005). Stress can impact physiology either indirectly through behaviours such as alcohol consumption and smoking, or directly through physiological changes such as changes in heart rate, blood pressure, immune function and endocrine response (Lovallo, 2005).
The physiological mechanisms involved begin with the Autonomic Nervous System (ANS). ANS is an unconscious control system which regulates digestion, heart rate, pupillary response, respiratory rate, sexual arousal and urination. It controls these functions using two different components, the Sympathetic Nervous System and the Parasympathetic Nervous System. Both systems originate in the spinal cord. The Sympathetic Nervous System triggers the release of stress hormones as part of the fight/ flight response activating physiological changes. The Parasympathetic Nervous System is responsible for returning the body to homeostasis ie its original calm before the fight/ flight response (Lovallo, 2005).
There are several models of stress proposed historically:
The Fight or Flight Model was proposed by Walter Cannon in 1929 and was the first to use the term stress in terms of demands on the body. Cannon coined the term fight/ flight response to describe the physiological reaction to a perceived threat in the environment. He also termed homeostasis as the process of maintaining internal stability (Lovallo, 2005).
Hans Selye later built on the research by Cannon and proposed the General Adaption Syndome model which is made up of three stages: Alarm – the fight/ flight response where stress hormones are released preparing the body for physical activity. Seyle argued this response also decreased the immune system leaving individuals vulnerable to disease. Resistance – during this stage the body will return to homeostasis, however if the perceived threat or condition persists the body will adapt to deal with this by continuing to resist, thereby remaining in state of arousal. Exhaustion – The final stage in GAS. When the body has remained in near continuous fight/ flight arousal it begins to lose the ability to oppose the stressors and decrease the harmful impact therefore exhausting itself. This in turn can cause: Reduction in the body’s resistance to stress; The immune system can become compromised, therefore unable to stave off disease; Reduced immunity due to chronic stress can cause heart attack, severe infection and/ or other diseases (Lovallo, 2005).
Worldwide, T2D has reached epidemic proportions. Since 1980 the number of people with a diagnosis of T2D has increased from 108 million to 422 million in 2014 (Diabetes, 2018) and is estimated to increase by 54% by 2030 (Spruijt-metz, Reilly, Cook, Page, & Quinn, 2014).
T2D is a chronic metabolic disease where there is not enough insulin, or the insulin released by the pancreas does not do its job in reducing blood sugar levels (“Type 2 diabetes”, 2018). T2D can lead to several comorbidities such as cardio-vascular disease, heart disease and stroke, to name but a few (“Type 2 diabetes”, 2018). T2D can be managed though lifestyle changes (diet, exercise) and medication, which requires a lot of self-management, This can be psychosocially and behaviourally demanding (Noordali, Cumming, & Thompson, 2017).
It is possible psychological stress can contribute to T2D, however the mechanisms surrounding this are still misunderstood (Carvalho, Urbanova, Hamer, Hackett, Lazzarino, & Steptoe, 2015). Research by Carvalho et al (2015) investigated whether stress responsiveness is linked to glucocorticoid and mineralocorticoid sensitivity. In a controlled experiment 37 people with T2D and 37 non-diabetic people underwent psychophysiological stress testing. The exclusion criteria for those with T2D was no history of coronary heart disease, inflammatory disease, allergies or mood disorders. In the healthy participants they had no history or objective signs of CHD, hypertension, diabetes, inflammatory diseases or allergies. Both groups underwent identical mental stress testing which consisted of two 5-minute mental tasks: a Stroop colour word interference test and a mirror tracing task (Carvalho et al., 2015).
The results showed people with T2D had a blunted stress responsivity in systolic blood pressure, diastolic blood pressure and heart rate. Post stress recovery in heart rate was also impaired. People with T2D also had higher levels of cortisol measured over the days and increased glucocorticoid sensitivity at baseline. They also suggest in diabetes modulation (Carvalho et al., 2015).
This study suggests that an impaired stress responsivity in people with T2D is due in part to a lack of stress-induced changed in mineralocorticoid and glucocorticoid sensitivity (Carvalho et al., 2015).
Limitations in this study are: Cross-sectional in nature therefore no causal conclusions can be drawn; Did no alter salivary cortisol levels due to the small sample size – results may differ if different stressors are used; cortisol stress reactivity may be different if measured in a different part of the day(Carvalho et al., 2015).
A positive psychological trait known to be linked to improved psychological and physical wellbeing is optimism. It is thought to also play a part in stress-related conditions such as metabolic syndrome and cardiovascular disease. Indirectly, it has an impact on health through health behaviours, and directly through psychophysiological processes. These pathways both affect the development of cardiovascular disease and other chronic illnesses (Puig-Perez, Hackett, Salvador, & Steptoe, 2017).
Puig-Perez, Hackett, Salvador, & Steptoe, (2017) conducted a study to assess the relationships between optimism, stress responsivity and daily cortisol output in people with T2D. Their hypothesis was that greater optimism would be related to heightened BP reactivity and better post-stress recovery in people with T2D and that no relationship was expected between optimism and acute cortisol response to stress; that greater optimism would be inversely associated with cortisol output over the day and expected optimism would be positively related to better self-related health (Puig-Perez et al., 2017).
140 participants with doctor diagnosed T2D took part in their study. None of the participants had a history of coronary heart disease, inflammatory disease, allergies or mood disorders. They were instructed to refrain from using antihistamines and anti-inflammatory medication for the 7 days prior to the study and were also told not to drink alcohol or do any intense exercise the night before. For the 2 hours prior to the study they were also not permitted to smoke or drink caffeine (Puig-Perez et al., 2017).
Optimism was measured using the 10-item Life Orientation Test-Revised (LOT-R) and, to establish a baseline, participants completed the questionnaire prior to the laboratory stress testing session. Subjective stress was measured before and at intervals after the testing using a 7-point rating scale. Objectives measurement were taken at the beginning of the session and included: Systolic Blood Pressure, Diastolic Blood Pressure, Heart Rate, Saliva samples for the assessment of cortisol were also taken (10 measures of cortisol were taken overall throughout the study). The laboratory stress consisted of two 5-minute mental tasks: a Stroop colour word interference test and a mirror tracing task (Puig-Perez et al., 2017).
Their main finding was people with low optimism and T2D showed a blunted SBP and DBP response to stress. There wasn’t any association between optimism and cortisol response to acute stress. Optimism was not related to the cortisol response to stress but did related to cardio vascular responses to stress in people with T2D and this agreed with previous studies. However, contrasting with other studies was the observation of a relationship with systolic blood pressure and diastolic blood pressure but not heart rate. They also found optimism is associated with heightened BP response to stress in those with T2D in the same way as that observed in healthy individuals. Their results also contribute to evidence supporting the protective effect of optimism in T2D. Their results were also supportive of the assumption that optimism helps people with T2D to have a better physiological adjustment to stress. Further supporting their hypothesis, they found low optimism was related to higher cortisol pattern in those people with T2D and finally optimism was linked to better self-related health (Puig-Perez et al., 2017). Based on their findings they propose that optimism has a protective role against the physiological effects of stress particularly in a diseased population, but further studies are needed in the area (Puig-Perez et al., 2017).
Limitations of this study included the sample recruited were all of white European origin with T2D without a history of coronary heart disease, therefore the results may differ in a different population. Also, the cortisol was only measured over one day which may have limitations on the ability to assess physiological functioning. Optimism was measured as a continuous measure whereas other studies see optimism and pessimism poles as distinct constructs. Optimism measured was based on past experiences. No information whether optimisms impacts hBa1c or medication usage in the study (Puig-Perez et al., 2017).
There is evidence in both studies of psychophysiological mechanisms are more pronounced in those with T2D compared to non-diabetics and stress impacts people with T2D in an adverse way increasing the chance of developing other comorbidities. However further research is required in this area.
Carvalho, L. A., Urbanova, L., Hamer, M., Hackett, R. A., Lazzarino, A. I., & Steptoe, A. (2015). Blunted glucocorticoid and mineralocorticoid sensitivity to stress in people with diabetes. Psychoneuroendocrinology, 51, 209–218.
Lovallo, W. (2005). Stress & health (2nd ed.). California: Sage Publications.
Noordali, F., Cumming, J., & Thompson, J. L. (2017). Effectiveness of mindfulness-based interventions on physiological and psychological complications in adults with diabetes: A systematic review. Journal of Health Psychology, 22(8), 965–983.
Puig-Perez, S., Hackett, R. A., Salvador, A., & Steptoe, A. (2017). Optimism moderates psychophysiological responses to stress in older people with Type 2 diabetes. Psychophysiology, 54(4), 536–543.
Spruijt-metz, D., Reilly, G. A. O., Cook, L., Page, K. A., & Quinn, C. (2014). Behavioral Contributions to the Pathogenesis of Type 2 Diabetes. Current Diabetes Reports., 14(4), 1–10.
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