The causes of intestinal dysbiosis: a review

Alternative Medicine Review, June, 2004 by Jason A. Hawrelak, Stephen P. Myers

A 1997 study assessed the effects of psychosocial stress on mucosal immunity, specifically the effect of emotional stress on secretory IgA (sIgA) levels. (60) The study was conducted on children ages 8-12 years (mean age 9.4 years). Ninety children were included in the trial--half of whom had a history of recurrent colds and flu, while the other half were healthy controls. The results demonstrated that stressful life events correlated with a decreased salivary ratio of sIgA to albumin. The ratio of sIgA to albumin controls for serum leakage of sIgA and is thought to give a clearer indication of mucosal immunity than total sIgA concentration. This result provides additional evidence of the likelihood of stress effectively decreasing mucosal immunity and, thus, diminishing intestinal colonization resistance.

Other studies on college students have found sIgA concentrations decrease during or shortly after examinations. (61) Salivary concentrations of sIgA are inversely associated with norepinephrine concentrations, suggesting sympathetic nervous system activation suppresses the production and/or release of sIgA. (60) Thus, frequent suppression of mucosal immunity by the sympathetic nervous system during stressful experiences could increase colonization of the intestinal mucosa by PPMs.

Holdeman et al studied factors that affect human fecal flora. They noted a 20-30 percent rise in the proportion of Bacteroides fragilis subsp. thetaiotaomicron in the feces of individuals in response 2to anger or fearful situations. When these situations were resolved, the concentration of these organisms in the feces decreased to normal levels. (62) This effect may be mediated via epinephrine, which has been shown to stimulate both intestinal motility and bile flow. As growth of B. fragilis subsp. thetaiotaomicron is enhanced by bile, this may partly explain the increased numbers of organisms in response to increased epinephrine release. (63)

In vitro experiments conducted by Ernst and Lyte have demonstrated that several neurochemicals have the ability to directly enhance the growth of PPMs. The influence of the catecholamines norepinephrine, epinephrine, dopamine, and dopa were assessed on two strains of Enterobacteriaceae--Yersinia enterocolitica and Escherichia coli, and one strain of Pseudomonadaceae--Pseudomonas aeruginosa. (64) All three bacterial species are potential pathogens, with Y enterocolitica (65) and E. coli (66) involved in GIT infections and P. aeruginosa in gastrointestinal, respiratory, and urinary tract infections. (67) The concentrations of catecholamines used in the experiment were equivalent to those found in plasma. The addition of norepinephrine, epinephrine, dopamine, and dopa to the cultures of E. coli resulted in increased growth when compared to non-catecholamine-supplemented control cultures. However, the largest increase in growth was observed with the addition of norepinephrine. Norepinephrine caused a large increase in growth of Y. enterocolitica, while both dopa and dopamine produced only small, but significant, increases in growth. Epinephrine demonstrated no effect. Norepinephrine also markedly increased the growth of P aeruginosa, while the other catecholamines appeared to have no effect on this organism. (64)