This piece is written by one of our contributors; neuroscience MSc student – Roshni Sandhu.
Stress is an inevitable part of our daily lives. It has become increasingly common to hear the word “stress” in our modern society, in the media and in our social circles. Stress has taken on quite a different meaning today as a response to the increased pressures of modern life and the vast array of demands placed on our time and energy. However, since the beginning of time, the stress response was utilised by our ancestors in order to avert threat and danger in the face of acute short term stressors and challenges. In a world where survival was dependent on speed, quick movements and the need to avoid being eaten by prey, our stress response has done us well in ensuring the survival of our species (1). The stress response continues to be adaptive today and in small doses is optimal for a variety of cellular, biochemical and metabolic functions. At the same time, chronic stress is having a negative and detrimental impact on our health as a population.
Thus, one of the major challenges we face today is: How do we understand and manage chronic stress appropriately in order to optimise our health and well-being?
What is Stress?
Stress is a difficult concept to define. For each individual, stress is precipitated by different factors and the way in which we experience stress also varies from person to person. Hans Selye, a prominent and early scientist in the field of stress research defined the concept in 1936 as “the nonspecific response of the body to any demand made upon it” (2). Selye suggested that stress was non-specific because he believed at the time that it did not involve emotions or the arousal of the nervous system. He also asserted that stress also occurs in species of plants and bacteria which lack nervous systems. This idea was later criticised as being too general, too biological and lacking in an understanding of both cognition and psychology (3).
Another stress researcher, Richard Lazarus, emphasised that stress can be defined as “the negative feelings and beliefs when people feel unable to cope with demands from the environment.” He believed that stress occurred when people lack the resources to deal with a stressful event and consequently become threatened. He also asserted that stress is subjective and that all stressors are not perceived equally by all people (4).
At present, more recent definitions point to the idea that in humans, stress is a response to both situations and events that pressure us. It is also significant to point out that our reactions to stressors will differ based on our genetics, our unique circumstances, environments and life experiences (5). In addition, stress encompasses our reactions to events. Stressors can range in their strength and severity. While it is generally expected that events which elicit stress are negative, this is not always the case. Positive events also have the ability to cause stress in a similar way. The key reason is because increased stress can be the result of a significant life event or change such as marriage, having a baby, preparing for a holiday, festival or large event or even planning and preparing to go on vacation. Although positive, these events elicit changes and accompany an increase in demands which in turn puts pressure on people (6).
The concept of stress is currently recognised and researched in a myriad of fields such as psychology, psychiatry, neuroscience, medicine, molecular biology, genetics, occupational health and public health (7). The representation of stress in all these fields and the fact that stress affects us all at various times and in different capacities points to it being an important subject worthy of discussion and further consideration.
The Biological Mechanism Behind Stress:
The stress response in the body is quite complex. It begins in the brain.
- When a stressor, danger or threat is perceived by the body, this information gets sent to an area of the brain called the amygdala. The amygdala is a part of the limbic system and is primarily used in the processing of emotions and in the fear response.
- When the amygdala receives the message that there is danger, a signal is sent to the hypothalamus. The hypothalamus is responsible for a variety of functions. It controls and regulates essential brain functions such as body temperature, heart rate, hunger, thirst, and fatigue. It is also the area of the brain which links both the nervous system and the endocrine system, the system that produces the body’s hormones.
- Next, the hypothalamus activates the autonomic nervous system. The autonomic nervous system is automatic. It works unconsciously and regulates blood pressure, breathing rate, heart rate, metabolism, water and electrolyte balance, digestion, urination, defecation and sexual responses. The autonomic nervous system has two components: the sympathetic nervous system also known as the “fight or flight” response and the parasympathetic nervous system or the “rest and digest” response.
- In response to a stressor, the autonomic nervous system communicates with the adrenal glands which in turn release adrenaline. This activates the sympathetic nervous system and causes physiological changes in the body. There is an increase in heart rate and sweating, the pupils dilate and the airways widen so more oxygen can enter the body and the brain. The body also releases stored energy in the form of glucose and fat and there is an increase in resting metabolic rate. These changes are meant to aid the body to act in an emergency. Concurrently, functions of the body which are not required to deal with the stressor at that time such as digestion and urination are slowed (8).
- The second component of the stress response, the central nervous system’s response, involves the hypo-thalamic pituitary axis (HPA), which involves the hypothalamus, pituitary gland and the adrenal glands. In response to stress, the hypothalamus releases corticotrophin releasing hormone (CRH). CRH travels to the pituitary gland and stimulates the release of another hormone adrenocorticotropic hormone (ACTH). ACTH then travels to the adrenal glands and binds to receptors on the adrenal cortex, causing the release of the hormone cortisol, the body’s main stress hormone. Cortisol is a glucocorticoid, a class of hormones which protects the body against inflammation.
- When the threat or stressor passes, cortisol levels drop and the body enters homeostasis or a balanced state. The parasympathetic nervous system then kicks in to counteract the stress response (8).
The Impact of Acute Stress on the Body:
Acute stress is an adaptive response. Adaptive responses maintain homeostasis in the body. In particular, stress hormones cause energy to be used by the body during the stress response. In addition, during acute stress, less important functions such as digestion are slowed and energy is utilized by the skeletal muscles and the brain. In the case of the stressor, these areas are more active. Therefore, it is adaptive for energy stores to be diverted to those areas (4).
- Acute stress improves memory. Stress hormones such as cortisol can lead to greater focus and an increase in short term memory (9).
- Short term stress is beneficial for performance and motivation. Cortisol increases the brain’s plasticity in small doses. Adrenaline increases the body’s attention and cognitive functioning (10).
- Acute stress also activates the immune system in a positive way, which helps to ward off infections. The stimulation of immune activity also heals wounds quickly (11).
The Impact of Chronic Stress on the Body:
Although the stress response is present in all humans and helps to regulate short term stressors, chronic stress has several negative impacts on the body and on health. When there is chronic stress, both the sympathetic nervous system as well as the HPA axis remain activated, which alters the body physiologically and makes it susceptible to illness and disease (4).
- Chronic stress has negative effects on the brain. It affects the hippocampus, the part of the brain responsible for the process of learning and memory. It reduces the volume of the hippocampus and also decreases neurogenesis (the growth of new nerve tissue) in these areas (12)(13). In turn, this can lead to decreased spatial memory (memory which records information about the environment) and disorders of declarative memory (memory of facts and events which are stored and can be consciously recalled). Cortisol has an inverse relationship with memory. This means that the more cortisol there is in the body, the more memory is impacted (14).
- Cognition is also impacted by chronic stress and involves important functions such as attention, decision making, learning and judgment. Chronic stress increases cortisol levels, which leads to changes in neural networks and hippocampal tissue. There is also a loss of dendrites, a part of the nerve cell which propagates electrical signals within the brain. Furthermore, stress leads to the loss of grey matter in the pre-frontal cortex, the area responsible for complex cognitive behaviour and executive functions such as decision making, planning, attention and reasoning (15).
- Chronic stress early on in life has a negative impact on both cognitive and emotional health. Individuals who experience early life stress, for example, poverty, abuse or neglect have a higher risk of developing mental health disorders such as anxiety and depression. This is due to the fact that early on in life, the brain is still developing and is therefore vulnerable. In turn, this may induce structural changes in the brain (16).
- The onset of chronic stress in adulthood may also increase one’s susceptibility to a wide range of mental health disorders. These include anxiety, depression, post-traumatic stress disorder, eating disorders, sleep disorders and schizophrenia (4)(17). The Mental Health Foundation UK’s 2018 study on stress levels, the largest known study of stress to date in the UK stated that 51% of adults who felt stressed reported feeling depressed and 61% reported feeling anxious (18).
- Stress is also linked to gastrointestinal disorders such as irritable bowel syndrome (IBS). It is now known that the central nervous system and the gastrointestinal (GI) tract are connected through the gut-brain axis. Therefore, chronic stress which affects the brain also affects the GI tract and leads to dysbiosis (the imbalance of bacteria), dysfunction in the gut, low grade inflammation and potential tissue damage (19).
- Chronic stress is linked to an increased rate of cardiovascular disease (CVD), as well as an increase in heart attacks and strokes. The hormones which mediate stress such as adrenaline contribute to hypertension, which is a risk factor for CVD. Furthermore, the stress response also contributes to atherosclerosis, which is thought to be due to a persistent increase in inflammation (20).
- Chronic stress suppresses immune function. Over time, it decreases leukocyte (white blood cell) numbers, and inhibits their function. This leads to a decrease in wound healing, a decreased resistance to both infection and cancer and an increase in both inflammation and auto-immune diseases such as lupus and rheumatoid arthritis (11).
- Chronic stress is linked to an increase in inflammation. Chronic stress leads to an increase in pro-inflammatory cytokines. When there is an increased production of cytokines, our body’s ability to fight infection is compromised. In addition, this inflammatory response has been linked to a whole host of health conditions such as cardiovascular disease, cancer, metabolic issues, mental health conditions such as depression as well as neurodegenerative diseases such as Parkinson’s disease (21).
The Mental Health Foundation UK’s 2018 study on stress levels noted that 74% of respondents have felt so stressed and overwhelmed they were unable to cope (16). Consequently, it is important that effective strategies to manage stress are implemented.
- Physical activity: Exercise reduces levels of both cortisol and adrenaline in the body. In addition, it releases endorphins which are the body’s natural painkillers and have beneficial effects on mood and reduces stress levels. TIP: UK government guidelines recommend 150 minutes of moderate intensity activity (brisk walking, cycling) or 75 minutes of vigorous intensity activity (running) or shorter durations of very vigorous activity (sprinting, stair climbing) or a combination of moderate, vigorous and very vigorous activity per week for adults. Muscle strengthening activities should be done at least two days a week (ex: resistance exercise, heavy gardening, carrying heavy shopping bags) (22).
- Social Support: Social support is defined as “the care or help from others that an individual can feel, notice or accept” (23). Social support is positively correlated with mental and physical health. In addition, one’s social network buffers against stress through helping individuals discuss and cope with stressors (24). 37% of respondents in the Mental Health Foundation UK’s 2018 study on stress who felt stressed said that they felt lonely as a result of their stress (16). TIP: Try to connect and spend quality time with those in your social network.
- Sleep: A lack of sleep results in an increase in stress hormones in the body. Furthermore, chronic sleep deprivation also places one at risk for developing mental health disorders such as depression (25). TIP: Aim to get 7-8 hours of restful, high quality sleep per night. Limit screen time two hours before sleeping as blue light from cell phones, computers and televisions disrupt the body’s circadian rhythms and disrupt sleep.
- Diet: During periods of stress, our body is depleted of nutrients and therefore these nutrients must be replenished. Furthermore, when stressed, individuals often skip meals or choose unhealthy options which are higher in fat and sugar content or “comfort foods” (26). 46% of respondents in the Mental Health Foundation UK’s study on stress levels reported that they ate too much or unhealthily and 29% of respondents started drinking alcohol or increasing their alcohol consumption as a result of stress (16). TIP: Eat nutritionally dense healthy whole foods. Try to incorporate a variety of colourful fruits and vegetables into your diet. Avoid excessive amounts of caffeine and alcohol.
- Relaxation Techniques: These techniques activate the parasympathetic nervous system and help to dampen the stress response:
- Breathing exercises: Taking long, slow deep breaths with focus. Breathe in through the nose for 4 seconds, hold the breath for 7 seconds, exhale through the mouth for 8 seconds.
- Meditation: A mental exercise involving concentration, observation and awareness to calm the mind. There are several different types and techniques of meditation which include visualization, focusing attention on breathing, reflection and resting awareness.
- Mindfulness: Focusing your thoughts on the present moment.
- Progressive muscle relaxation (PMR): Used to relieve muscle tension, stress and anxiety by progressively tensing groups of muscles in the body and subsequently relaxing them.
- Yoga, tai-chi and qi-gong: Using various postures and movements along with steady breathing to increase clarity and mental focus.
TIP: Try to incorporate some of these techniques into your overall daily routine in order to manage your stress levels.
- Self-Care: Take some time out for yourself to do the things you enjoy.
NB: If you feel your symptoms of stress are overwhelming and affecting your quality of life/ability to carry out daily functions, please reach out to a health care professional or provider (your GP, a psychologist/therapist).
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