Environmental factors driving susceptibility to depression; psychosocial or microbiological?

By Graham Rook

Chronic inflammatory disorders (allergies, autoimmunity, IBD) have increased dramatically in developed countries. But depression is strongly associated with these disorders and should therefore be increasing in parallel. While there is no universal agreement, there is evidence that rates of depression are indeed increasing (discussed and referenced in Raison et al., 2010). Moreover, moving from the developing world to the U.S. increases the risk. For example, Mexican immigrants to the U.S. have rates of depression similar to those seen in Mexico. However, individuals of Mexican descent born in the U.S. have higher rates that are equivalent to those of the U.S. population at large, suggesting that it is the American lifestyle rather than acculturation shock that accounts for the increase (Vega et al., 2004). Interestingly there is also a significantly higher risk of mood and anxiety disorders in urban populations, compared to rural ones (Peen et al., 2010).

These findings all imply an environmental trigger that is more prevalent in developed and urban situations than in undeveloped and rural ones. But what is this environmental trigger? (more…)

Genes essential to the immune system that are “entrusted” to microbial “Old Friends”

In 2005 Sarkis Mazmanian and colleagues showed that a single polysaccharide from an intestinal commensal, Bacteroides fragilis, could largely correct the subnormal and functionally distorted development of the immune system that occurs in germ-free mice (Mazmanian et al. 2005). More recently they have shown, using three different models of intestinal inflammation, that the same polysaccharide, given by mouth, can turn on crucial immunoregulatory pathways (Mazmanian et al. 2008). In the discussion of the latter paper they state:- (more…)