Association between insulin-like growth factor status and physical activity levels in rheumatoid arthritis

Objective. To determine if the altered insulin-like growth factor (IGF) sta tus in rheumatoid arthritis (RA) is due to inflammation, altered body compo sition, or lack of exercise. Methods. Subjects included 73 patients with RA, 54 patients with other rheu matic diseases, both inflammatory and noninflammatory, and 28 healthy, phys ically active controls. Serum levels of IGF-I, IGF-III and IGF binding prot ein-3 (IGFBP-3) were measured by radioimmunoassay. Body composition was est imated by bioelectrical impedance analysis, and habitual exercise level app roximated by questionnaire. Statistical analysis was performed by 2 and 3 w ay ANOVA and moderated hierarchical regression. Results. Serum IGF-I (p < 0.001), IGFBP-3 (p < 0.001), and the BP-3:total I GF molar ratio (p < 0.001) were depressed in both patient groups relative t o controls. In contrast, IGF-II levels were depressed only in patients with RA (p < 0.01). Differences in the IGF proteins between patients and contro ls could not be attributed to inflammation. Habitual exercise level, but no t body composition, was shown to be a significant predictor for IGF-I, IGFB P-3, and BP-3:total IGF molar ratio (p < 0.001). Conclusion. Our results indicate that the reduction in circulating IGF prot eins observed in our patients is more related to their sedentary lifestyle than to the inflammatory process. This conclusion is in agree ment with rep orts that show that highly active individuals typically exhibit higher leve ls of systemic IGF proteins than age matched sedentary controls.