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…)