Objective: To examine whether the activation of indoleamine 2,3-dioxygenase (IDO), an enzyme involved in serotonin production, is associated with depressive symptoms.
Methods: The participants were 544 women and 442 men (aged 24-39 years) from the population-based Young Finns Study who participated in a medical examination in 2001 (including IDO and depression) and 2007 (follow-up assessment for depression).
Results: At baseline, IDO was associated with depressive symptoms (in the total cohort: B = 0.23, p < .001; women: B = 0.20, p = .007; men: B = 0.29, p = .002; p for interaction = .19). IDO at baseline was also associated with depressive symptoms at follow-up in women (B = 0.17, p = .03), which remained significant when adjusting for any of the biologic and behavioral risk factors. Adjusting for body mass index attenuated the association by 6%. In the final model including all baseline variables, none of the risk factors (except for baseline depressive symptoms) were associated with depressive symptoms at follow-up.
Conclusions: These data suggest that IDO activity may be a risk factor for future depression especially in women. IDO-induced alterations in serotonergic function may offer one biologic explanation to the well-established associations between inflammation and depression.