There is a fascinating article on The Scientist web site about "Neurotransmitter-Regulated Immunity."
It reports on a pair of research articles delving into the relationship between our brains and our immune responses. The experiments were done on mice. Normally, I resist paying much attention to animal experiments, because they often turn out to not really tell us much about human health. But these research efforts are shining some light on basic mechanisms that could help explain phenomena that we've all seen play out in real life.
One of the most consistent observations in population health is that people in wealthier neighborhoods tend to be healthier and live longer than those in poor neighborhoods. What is particularly striking is that even after you take into account differences in lifestyle (smoking, physical activity, body weight) some of the discrepancies persist.
Then there is the data indicating that people with higher status jobs tend to be healthier than those at the bottom of the work hierarchy. Again, some of the difference persists even when researchers try to factor in lifestyle and other characteristics. It seems there is something about being at the top of the heap that translates into better health.
These health disparities are also seen in countries (Britain for example) that have universal health care coverage and where the differences in the kind of health care available to rich and poor are much less extreme than in the United States.
Along the same lines, researchers continue to investigate how racism itself might explain some of the health disparities between members of majority and minority communities.
Stress has been offered as one potential explanation for a link between social factors and physical health. Much of the attention has gone to corticosteroids. These naturally-occurring hormones (also distilled for use as medications) can sometimes suppress immune function.
The research discussed in The Scientist involves a different set of substances in our bodies, including acetylcholine and noradrenalin. The animal research indicated these neurotransmitters can affect how the immune system works.
Maybe it's another piece of the machinery that connects how we live, how we feel... and how likely we are to get sick and die.