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.