Cross-sectional and longitudinal associations between insulin-like growth factor I and metabolic syndrome: a general population study in German adults.

BACKGROUND: A previous study showed an inverse association between the insulin-like growth factor I (IGF-I) and the risk of impaired glucose tolerance or diabetes mellitus. Moreover, myocardial infarction patients with high baseline IGF-I levels had a lower risk of diabetes mellitus. These data suggested a protective effect of IGF-I against the development of metabolic syndrome. However, there are no longitudinal data regarding IGF-I and metabolic syndrome. The aim of the present study was to investigate the longitudinal association between IGF-I and metabolic syndrome.
METHODS: Data from the population-based Study of Health in Pomerania, Germany, were used for cross-sectional (n = 3903) and longitudinal (n = 2143) analyses (5-year follow-up). Metabolic syndrome was defined by three or more of the following five components: abdominal obesity, elevated triglycerides, reduced high-density lipoprotein cholesterol, elevated blood pressure and elevated nonfasting glucose. Serum IGF-I and IGF binding protein 3 (IGFBP-3) were determined by chemiluminescence immunoassays. Logistic and Poisson regression analyses were performed to determine associations.
RESULTS: In cross-sectional analyses high IGFBP-3 as well as high and low IGF-I/IGFBP-3 ratio levels were associated with prevalent metabolic syndrome. In longitudinal analyses, the direction of the relation changed: men but not women with high IGF-I or IGF-I/IGFBP-3 ratio levels had an increased, whereas men with low levels had a decreased risk of incident metabolic syndrome.
CONCLUSION: In concordance with previous studies, our cross-sectional analyses showed a relation between low IGF-I/IGFBP-3 ratio and the prevalence of metabolic syndrome. In contrast, the longitudinal analyses indicated that a high IGF-I level was a risk marker for incident metabolic syndrome.