people sad, disheartened, worthless, irritable and restless. They lose interest
in any kind of social activity and prefer isolation.
Sickness behavior, on
the other hand, is described as "a coordinated set of adaptive behavioral
changes that develop in ill individuals during the course of an infection."
Sickness behavior affects the lifestyle of an individual by bringing about
changes like excessive sleep, fatigue, and sometimes insomnia,
loss of energy, aches and digestive problems.
Sickness behavior is
the body's response to immune trauma and infections and is known to be mediated
by pro-inflammatory cytokines. It is a
protective mechanism of the body to accelerate recovery by energy conservation.
For example, fever accompanying sickness behavior helps to fight infection.
Certain similarities exist between depression and sickness behavior such as
fatigue, sleepiness and failure to concentrate. In addition, the three symptom
dimensions of depression, which are melancholia (a failure to react to
pleasurable stimuli, and excessive psychomotor retardation and weight loss),
anxiety, and physio-somatic symptoms like increased sensitivity to pain are
also observed in sickness behavior.
There are also some
differences between the two conditions. Symptoms of depression not observed in
sickness syndrome include suicidal ideation, symptoms of guilt and
worthlessness, excessive eating and weight gain. Depression is usually a
progressively worsening condition associated with functional deterioration. On
the other hand, sickness behavior is an acute, short-term state where the body
aims to combat an infection or trauma and hence enhance recovery.
The researchers note
that "Translational studies show that inflammatory pathways may account for
sickness behaviour as well as clinical depression and, therefore, may explain
the partial phenomenological overlap between both conditions."
Thus, though both
these conditions share common inflammatory pathways, the inflammatory pathways
provoke two different responses, a beneficial sickness behavior which is a
compensatory reflex reaction, and clinical depression, which is a progressive
Depression and sickness behavior are Janus-faced
responses to shared inflammatory pathways; Michael Maes et al; BMC Medicine