IGF-I levels and depressive disorders: results from the Study of Health in Pomerania (SHIP).

In vitro and in vivo models revealed that the somatotropic system exerts central effects on the central nervous system. Disturbances to this system such as in the case of growth hormone deficiency or growth hormone excess, are associated with a wide range of psychiatric disorders. Nonetheless, there is no epidemiological data available regarding the influence of growth hormone and its mediator, insulin-like growth factor I (IGF-I), on depressive disorders. The objective of this study was to investigate whether endogenous IGF-I levels may predict depression in humans. We included 4079 adult subjects from the Study of Health in Pomerania (SHIP), a population-based study with a 5-year follow-up period. The main predictor was the baseline IGF-I value categorized in three levels as <10th percentile, between the 10th and the 90th percentile (the reference group) and >90th percentile. The outcome measure was the incidence of depressive disorders according to the Composite International Diagnostic-Screener (CID-S). After adjustment for potential confounding variables, females with IGF-I levels below the 10th percentile had a higher incidence of depressive disorders during follow-up (OR 2.70 95% CI 1.38-5.28, p=0.004) compared to females within the reference group (10th-90th percentile). Among males, those with IGF-I levels above the 90th percentile had a higher risk of depressive disorder (OR 3.26 95% CI 1.52-6.98, p=0.002) than those within the 10th-90th percentile. In conclusion we can demonstrate that low IGF-I levels in females and high IGF-I levels in males predict the development of depressive disorders in this general adult population sample.