Stress and Infectious Disease
Stress refers to the physical or psychological pressure that individuals experience, which can manifest in worry or tension. Infectious diseases, on the other hand, are illnesses caused by pathogens like bacteria and viruses. Research has established a significant link between stress and the development of infectious diseases, suggesting that chronic stress can weaken the immune system and increase susceptibility to infections.
According to the general adaptation syndrome model proposed by Hans Selye, the body undergoes three stages in response to stress: alarm, resistance, and exhaustion. Chronic stress can lead to various health issues, including weakened immunity, increased risk of infections such as colds and flu, and several chronic health problems. Studies have shown that psychological stress correlates with a higher incidence of respiratory infections, and recent investigations during the COVID-19 pandemic have highlighted the association between long-term stress and greater vulnerability to severe illness.
The economic ramifications of stress-related infections are substantial, impacting workplace productivity, healthcare costs, and educational outcomes. As such, integrating stress management into public health initiatives is increasingly recognized as vital for improving health outcomes and reducing the burden of stress-related diseases.
Stress and Infectious Disease
Definition: Stress is physical or psychological pressure, worry, or tension. Infectious diseases are illnesses of the human body caused by pathogens such as bacteria and viruses. Research has linked stress to the development of infectious diseases in humans.
Stress and the Human Body
In 1936, scientist Hans Selye introduced his general adaption syndrome model, which describes how the human body attempts to restore homeostasis when subjected to physical stress that threatens life. Selye, the founder of stress research, believed that human bodies react in predictable ways to external stressors, and that chronic exposure to stress could change the body chemically, resulting in disease. Selye’s three-step model included stages of alarm, resistance, and exhaustion.
In the alarm stage, the body experiences hormonal changes to address the perceived threat. The body’s defenses activate the hypothalamic-pituitary-adrenal axis, sympathetic nervous system, and adrenal glands to release chemicals such as cortisol, adrenaline, and noradrenaline. Catecholamines produce an emotional response, such as fear. The immune systemmobilizes to respond to the threat, equipping the body with the chemical energy needed to “fight or take flight.”
The second stage of stress is resistance, in which the body attempts to return to homeostasis. Metabolic changes keep the body functioning. If the threat continues, the body stays stressed without recovery, leading to stage three, exhaustion. All reserves are used up. Fatigue, burnout, dysfunction, impaired thinking, and damage to body cells and tissues occur, resulting in disease. In experimental animals, repeated severe stress resulted in physiological changes such as a smaller thymus gland, gastrointestinal ulcers, larger adrenal glands, and sometimes death.
Types of Stress
Many scientists have studied the concept of stress for decades. Stress is commonly categorized as acute or chronic. Acute stress involves an immediate threat that causes an alarm reaction. An example of acute stress is stepping on a snake or being frightened by an unknown noise at night. When the stress passes, the body recovers and relaxes.
With chronic stress, such as long-term disease or job, financial, or relationship worries, the body remains threatened. This does not allow the body to recover, lowering the immune response and putting the body at risk for illness. Diseases that can result from long-term stress include severe headaches, high blood pressure, depression, stomach ulcers, and increased incidence of colds, the flu, and other infections.
Research
To investigate if stress decreases host resistance to infection, Sheldon Cohen and colleagues studied the connection between psychological stress and the common cold resulting from respiratory viruses in 1991. They found that the incidence of common colds increased in a dose-response manner with psychological stress. These scientists from Carnegie Mellon University concluded that increased psychological stress was directly related to increased infection rates from respiratory viruses.
In 1993, T. W. Klein of the University of South Florida College of Medicine found that neuroendocrine hormones can change the functioning of immune cells. His experimental studies demonstrated a connection between stress and infection, with human subjects under increased stress more likely to contract a disease with a cold virus.
In 1998, Cohen and colleagues published a study on life stressors and the common cold in the journal Health Psychology. The study aimed to define the nature of life stressors and the biological link to disease susceptibility. The researchers looked at white blood cell activity and natural killer (NK) cell activity in the host's blood sample before the virus "challenge." Epinephrine, norepinephrine, and cortisol were measured in urine the day before host exposure to the virus. The study's results showed that the total infection rate was eighty-four percent.
Scientists continue to look at ways that stress impacts infectious diseases. In 2009, researchers at the University of Saskatchewan published an article in the International Journal of General Medicine reviewing modern approaches to stress and infectious disease, emphasizing respiratory illnesses. The researchers claimed stress can affect levels of specific hormones that activate or suppress the immune system. However, the study focused on how stress affects disease suscepstibility and how new medical approaches can address remaining complex questions.
Further investigations conducted amid the COVID pandemic have presented proof of the link, between stress and infection risks as indicated by recent studies revealing that persistent stress is linked to heightened vulnerability to contracting COVID and experiencing more severe illness outcomes as a result. A comprehensive meta analysis undertaken in 2023 encompassing an array of studies demonstrated that individuals, under psychological stress, faced a 58 percent greater likelihood of contracting viral respiratory infections and exhibited slower recovery rates.
Impact
Stress-related infections continue to have profound societal and economic consequences. Data from 2019 showed workplace productivity losses from stress-related infections nearly doubled to $45 billion annually, with remote work introducing new challenges in tracking and managing illness-related absences. Healthcare spending on treating stress-related infectious diseases reached $8 billion annually, while stress-related absence rates increased twelve percent since 2019.
The educational sector saw similar impacts, with students missing 240 million school days annually due to infectious illnesses percent of which are linked to stress-compromised immunity. Distance learning has added complexity, with 164 million learning days lost due to illness in in 2023. The healthcare system faces mounting pressure, experiencing a 32 percent increase in stress-related infectious disease hospitalizations, with mental health conditions worsening infection outcomes by 45 percent.
The impact of the COVID-19 crisis brought attention to how psychological stress can affect susceptibility to infections. It is notable that Medicare and Medicaid allocate about $12 billion each year to tackle diseases caused by stress emphasizing the increasing strain on public healthcare systems. This increasing evidence of stress's role in infection susceptibility and severity reinforced the critical need for incorporating stress management into broader public health strategies.
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