Stress and Allergies: The Surprising Link

STRESS AND ALLERGIES: THE SURPRISING LINK

Researchers are uncovering a surprising link between the stress response and allergic reactions. They’ve noted both an underactive and overactive stress response in individuals with allergic conditions, indicating that dysregulation of this physiologic response may play a role in the development or exacerbation of allergies.

THE PHYSIOLOGY OF STRESS AND ALLERGIES

The stress response is mediated through the sympathetic nervous system and the hypothalamus-pituitary-adrenal (HPA) axis. These are normal physiologic processes for reaction during stressful circumstances.

The sympathetic nervous system responds by increasing the secretion of catecholamines from the adrenal gland including epinehrine (adrenaline) and norepinephrine. This results in enhanced heart and respiratory rate, sweating and decreased intestinal motility, as well as directing blood to muscles and away from organs.

The HPA axis is a cascade of activation resulting in increased secretion of cortisol from the adrenal gland. Cortisol elicits changes throughout the body including altering the immune response, blood sugar, blood pressure, bone formation, cognition and digestion. Prolonged elevation of cortisol or the inability to maintain high hormone output with prolonged activation may result in deleterious health effects.

Allergies are mediated by a hypersensitivity reaction of the immune system in which the immune system responds to harmless proteins (antigens). Allergic reactions involve antibodies, which are proteins formed by white blood cells known as B-lymphocytes. These proteins, also known as immunoglobulins (Ig), bind to proteins and cause the release of several pro-inflammatory chemical mediators. IgE is the antibody most commonly associated with allergic reactions. Other white blood cells including mast cells, basophils and eosinophils release chemicals such as histamine involved in allergic responses.

THE RELATIONSHIP BETWEEN STRESS AND ALLERGIES

Research indicates that environmental factors such as stress play a significant role in the development of allergies. Scientists propose that a dysfunctional HPA axis in response to stress may facilitate changes in the immune response and thus, could increase the risk for allergic sensitization and exacerbation, particularly under stressful conditions.

Several interesting studies indicate that infants under stress who have elevated cortisol levels are more likely to develop allergies, and conversely, infants with lower cortisol are less likely to develop allergic conditions. In one study published in December 2011, researchers measured salivary cortisol in infants at six months of age and three times during a single day. Scientists determined IgE levels from blood samples taken at six, 12 and 24 months of age. The researchers found that elevated morning cortisol was associated with a 60 percent increase in the likelihood f IgE sensitization and a 28 percent increase in the likelihood of allergic skin conditions. Elevated afternoon cortisol was associated with a 56 percent increase in the likelihood of IgE sensitization and a 33 percent increase in the likelihood of allergic skin reactions, while elevated evening cortisol showed a 49 percent increase in the likelihood of IgE sensitization and 37 percent increase in the likelihood of allergic skin conditions.

A study published in July 2004 evaluated cortisol levels related to the heel-prick in newborns. Researchers compared cortisol levels between newborns who had a family history of atopy, and newborns without atopic predisposition. Scientists also measured IgE levels from cord blood. Cortisol levels were significantly higher in response to the heel-prick in newborns with a family history of atopy and in the newborns with elevated IgE. Thus, the study authors concluded that atopic disposition in neonates is associated with altered responsiveness of the HPA axis  to stress, which may increase the vulnerability to develop allergic manifestations later in life.

In a study published in September 2002, scientists compared subjects who had allergic skin conditions to healthy control subjects and evaluated them for both HPA axis and sympathetic nervous system activation in response to a laboratory stressor consisting of a free speech and mental arithmetic task in front of an audience. The subjects with the allergic skin condition showed blunted cortisol response to the stressor compared to the healthy subjects. However, the subject with the allergic condition showed a heightened sympathetic nervous system response with elevated catecholamines compared to the control group. Other research demonstrates that psychological stressors cause an increase in eosinophils, allergy-related T-lymphocytes, and alter the chemical mediators released from immune cells.

SUPPORTING A BALANCED STRESS AND IMMUNE RESPONSE

Research demonstrates numerous variables that impact both the stress and allergic response. Specifically, exercise, healthy weight, diet and certain adaptogens can significantly impact the immune and stress response.

Exercise. Exercise modulates the HPA axis, depending on the intensity. Studies indicate that low-intensity exercise lowers cortisol levels, while high-intensity exercise can elevate cortisol. In a study published in July 2008, moderately trained men participated in 30-minute exercise regimes and were evaluated for HPA responsiveness. The investigators found that low-intensity exercise resulted in lower cortisol levels.

In another study published in May 2005, aerobically fit and unfit women were evaluated for HPA response to a psychological stressor. The older-unfit women had significantly greater cortisol responses to the challenge than both the young-unfit and the older-fit women. The study authors stated that higher aerobics fitness among older women could attenuate these changes as indicated by an attenuated cortisol response to psychological stress.

During allergy season, patients may consider exercising in a gym or in the morning (5 to 10 a.m.) and mid-evening when pollen counts are lower.

Weight. Numerous studies demonstrate that weight management influences allergic symptoms as well as stress response. Adipose (fat) tissue products pro-inflammatory chemical mediators (adipokines), which pushes the immune system towards allergic-type responses. In one study published in January 2012, researchers demonstrated that an elevated body mass index (BMI) at one, four and/or seven years of age was associated with an increased likelihood of allergic lung conditions and sensitization to inhaled allergens at eight years of age.

Weight is also correlated to allergic symptoms in adults. Individuals with allergic lung conditions are more likely to be overweight than healthy controls, and the severity of the lung symptoms correlated with the extent of excessive weight. Similarly, overweight adults are more likely to have allergic lung hyperreactivity and elevated IgE.

Studies also indicate that visceral (abdominal) fat accumulation is related to dysregulation of the HPA axis functioning under normal as well as challenged conditions. For example, in one study published in June 2010, waist-to-hip ratio in women and fat mass index and waist circumference in men correlated to alteration in HPA response and cortisol levels.