It has become widely accepted that the immune system, and specifically increased levels
of inflammation, play a role in the development of depression. However, not everyone with
increased inflammation develops depression, and as with all other diseases, there are risk
factors that may contribute to an increased vulnerability in certain individuals. One such
risk factor could be the timing of an inflammatory exposure. Here, using a combination of
PubMed, EMBASE, Ovid Medline and PsycINFO, we systematically reviewed whether exposure to
medically related inflammation in utero, in childhood, and in
adolescence, increases the risk for depression in adulthood. Moreover, we tried to
determine whether there was sufficient evidence to identify a particular time point during
the developmental trajectory in which an immune insult could be more damaging. While
animal research shows that early life exposure to inflammation increases susceptibility to
anxiety- and depressive-like behaviour, human studies surprisingly find little evidence to
support the notion that medically related inflammation in utero and in
adolescence contributes to an increased risk of developing depression in later life.
However, we did find an association between childhood inflammation and later life
depression, with most studies reporting a significantly increased risk of depression in
adults who were exposed to inflammation as children. More robust clinical research,
measuring direct markers of inflammation throughout the life course, is greatly needed to
expand on, and definitively address, the important research questions raised in this
review.