The association between the presence of TPOAb and depression has been unclear. Though, most studies investigating the relationship between thyroid function and depression measured just the current presence of depressive symptoms, thus focused on state* characteristics of depression.
It may be questioned whether thyroid function is more distinctly associated with trait** markers. A study based on a large population-based survey in the Netherlands explored this hypothesis. They found no significant relationship between the presence of TPOAb and state markers of depression in the general population. Though, the presence of TPOAb is associated with trait characteristics of depression like neuroticism scores and a lifetime diagnosis of depression. One explanation is that the association between TPOAb and trait characteristics of depression more likely is the result of a co-association with another factor, like predisposition for autoimmunity and is not a result of causal relationship.
State* is a momentary emotional reaction to internal and/or external trigger and our physical, behavioural, cognitive and psychological reaction to it.
Trait ** presents the tendency of an individual to habitually feel, think and behave in a certain way and it is generalized in many different situations and contexts. Traits are stable in time.