How Stress Makes You Ill

One of the most important aspects of what separates harmless stress
from the stress that makes you ill is duration. We can cope with a
brief period of stress, so long as it isn't too traumatic or
overwhelming. The problems arise when we stay stressed for long
periods of time, because it's not what we're designed for. We are
designed for life on the primordial plane millions of years ago.
Natural selection adapted us very well for that environment. Our basic
design hasn't moved on a lot since then because few things in our
present lives threaten our ability to make it to child-bearing age. In
those days life was mostly very dull, interspersed occasionally by
short periods of extreme danger or opportunity. If an antelope passes
your cave, you've got about 20 seconds to do something about it, or
you and your family won't eat for a week. If, on the other hand, you
emerge from your cave to be confronted by a sabre-tooth tiger, what
you do over the next 20 seconds will determine whether you pass on
your genes or not. So we got very good at dealing with short periods
of stress. The hormone adrenaline was evolved to cause a range of
changes to the body to occur very quickly when the need arises. It
does a brilliant job, turning us into finely adapted machines able to
fight or to run at the peak of our body's capacity.Within a few
heartbeats, adrenaline, released by the body in response to perceived
threat, affects almost every bodily function. The heart beats faster,
to pump more blood around the body, we become breathless so as to load
up with more oxygen, the blood vessels to the muscles and the skin
dilate, to allow greater muscular activity and to lose heat, which we
are sure to generate in our flight from the beast that is chasing us
and all our nerves become super-sensitive as we are going to need all
possible acuity in the life or death struggle ahead. In addition, the
bowels will tend to open up at both ends, as this can allow a rapid
jettisoning of a few pounds of body weight, helpful in running faster
and will lay a powerful scent trail. As most of our predators in those
days relied heavily on their sense of smell, while we don't, the
confusion that this causes gives us a few seconds to find a crevice to
crawl into to avoid being eaten.All highly adaptive if you're being
pursued by a sabre-tooth tiger, but little use to you if you're
sitting in an office, or a restaurant, or at home.So adrenaline makes
us well-adapted to short-term stresses. The problem is that that isn't
the way our modern world is constructed. There are few wild animals
threatening to eat us and most short-term threats to life and limb
have been eradicated. The threats we face are more subtle, more
subjective and much longer lasting. We aren't designed for that. So we
suffer the effects of stress, rather than being enhanced by them and
the same heightened arousal that protected our ancestors makes us ill.
Natural selection doesn't care. Most of the physical effects of
chronic stress don't threaten our lives until after the normal
reproductive years, and as far as natural selection is concerned we
are, by then, disposable.