The severity of obstructive sleep apnoea does not influence ambient IGF-I levels

Objective Obstructive sleep apnoea (OSA) is reported to have effects on a number of hormone systems including the hypothalamo-pituitary axis. We aimed to determine the impact of OSA severity on insulin-like growth factor-I (IGF-I) levels. Design and Methods This is a prospective cohort study performed between November 2014 and May 2017. IGF-I was measured on serum samples, and data were collected on demographics, BMI and parameters of OSA. Results 611 participants were recruited (202 female, 53.5 +/- 12.5 years; mean BMI 36.2 +/- 8.0 kg/m(2)). 26.2% had mild OSA; 27.3%, moderate OSA; and 44.5%, severe OSA. 15.2% of IGF-I values were below the age-related reference range. Increasing BMI correlated with greater AHI (r = .28, p < .001), ODI (r = .30, p < .001), severity of OSA (r = .17, p < .001), duration with oxygen saturation (SaO(2)) <90% (r = .29, p = .001) and reduced median SaO(2) levels (r = .19, p < .001). IGF-I levels correlated negatively with age (r = -.13, p = .001), BMI (r = -.16, p < .001), diabetes (r = -.108, p = .009), AHI (r = -0.10, p = .043) and severity of OSA (r = -.10, p = .013). No association of IGF-I was observed with ODI, median SaO(2) levels or duration of SaO(2) < 90%. Regression analyses were used to examine determinants of IGF-I, all of which contained the independent variables of age, gender and BMI. All models showed IGF-I to be predicted by age and BMI (p < .05); however, none of the parameters of OSA were significant within these models. Conclusion Insulin-like growth factor-I levels in OSA are dependent on age and BMI; however, no additional effect of any OSA parameter was observed, supporting the hypothesis that OSA effects on IGF-I are indirect through concomitant body composition and metabolic parameters.