What is the relationship between stress and infectious disease?

Definition

Stress is physical or psychological pressure, worry, or
tension. Infectious diseases are those illnesses of the human body caused by pathogenic organisms
such as bacteria and viruses. Research has linked stress to the development of
infectious disease 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 (balance) 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 noradrenalin. Catecholamines produce an emotional response, such as fear.
The immune
system mobilizes 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, and dysfunction, along with 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

The concept of stress has been studied by many scientists for decades. Stress is commonly categorized as acute or chronic. Acute stress involves an immediate threat that causes the 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 in a threatened state. This does not allow
the body to recover, and it lowers the immune response, 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 (in 1991) studied the connection between psychological stress and
the common
cold resulting from respiratory viruses. 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 rates of infection 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 an infection with a cold virus.

Cohen and colleagues (in 1998) published a study related to life stressors and
the common cold in the journal Health Psychology. The study’s
goal was 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.”
The hormones epinephrine, norepinephrine, and cortisol were measured in
urine the day before host exposure to the virus. The results of the study showed
that the total rate of infection was 84 percent.

Scientists continue to look at ways that stress impacts infectious disease. 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, with emphases on respiratory illnesses. The researchers claimed that stress can affect levels of specific hormones that activate or suppress the immune system. However, the focus of the study was on how stress affects disease susceptibility and on how new medical approaches can address remaining complex questions.

Impact

Stress affects everyone, even though human experience, perception, and response varies. Stress can be either mental or physical, or both. Physical symptoms that plague the general population, such as headaches or insomnia, often occur with stress and result in lost days from work and school. Research on the common cold and other respiratory infections has linked infections to stress.

More than one billion people experience colds each year. The impact of the common cold on the work force can be quantified: about 23 million days of work at a cost of $25 billion in lost productivity each year. Some 26 million school days are missed by students sick with colds each year, impacting the educational system and student learning. About $2.5 billion is spent to treat colds annually, aiding the pharmaceutical industry.

Stress and resulting infections greatly affect the function and economic well-being of the general population, health and medical care, business and industry, health insurance, and government, which, in the United States, for example, assumes the costs of health care for persons on Medicare and Medicaid. Discovering the relationship of stress to costly and life-altering infections can encourage new ways to cope with day-to-day and chronic stresses for improved health and quality of life.

Bibliography

Ader, Robert, ed. Psychoneuroimmunology. 4th ed. Boston: Academic Press/Elsevier, 2007. A classic text in the field of psychoneuroimmunology, the study of interactions between psychology and the immune and nervous systems of the human body.

Cohen, Sheldon, et al. “Types of Stressors that Increase Susceptibility to the Common Cold in Healthy Adults.” Healthy Psychology 17, no. 3 (1998): 214-223. Details a follow-up study from Cohen’s work in 1991 regarding the relationship of stress to the common cold.

Cooper, Cary L. Handbook of Stress Medicine and Health. 2d ed. Boca Raton, Fla.: CRC Press, 2005. Reviews stress and its direct relationship to health, long-term stress, and the immune system.

Lovallo, William R. Stress and Health: Biological and Physiological Interactions. Thousand Oaks, Calif.: Sage, 2005. Explains links among stress, health, and disease, with attention to the psycho-physiological responses of the body to stress.

Steptoe, Andrew, and Jane Wardle, eds. Psychosocial Processes and Health: A Reader. New York: Cambridge University Press, 1994. Contains research studies on various aspects of health, including life stress and psycho-physiological processes in disease.