The volunteers were asked to complete a series of tasks meant to stress most anyone out: First, they gave a speech in front of people in lab coats about why they deserved their dream job. Then, they had to count backwards in increments of 17 from 3,079.

Following the tests, the men who were raised in cities were found on average to have higher levels of certain blood cells and proteins in their blood. These specific components of the immune system, known as peripheral blood mononuclear cells (PBMCs) and interleukin 6, indicate a strong inflammatory immune response. The city men also had elevated levels of these markers for longerat least up to two hours, when they stopped having their blood drawn.

While inflammation is a crucial part of a healthy immune system, previous research has suggested that people who have chronic, low levels of inflammation are at higher risk of developing mental health disorders like major depression. The studys findings suggest that city-raised people might be more likely to fit this bill, though more research would be needed to definitively make that connection.