Study objectives: To assess the time-dependent effect of continuous positive airway pressure (CPAP), on insulin-like growth factor-1 (IGF-1), IGF binding proteins (IGFBPs) and pulsatile growth hormone (GH) secretion.
Design: A randomized, double-blind, sham-controlled, parallel group study.
Participants: Sixty-five middle-aged men with moderate to severe obstructive sleep apnea.
Intervention: Active (n = 34) or sham (n = 31) CPAP for 12 weeks, followed by 12 weeks of active CPAP (n = 65).
Measurements and results: Fasting morning IGF-1, IGFBP-3, and IGFBP-1 blood levels at 0, 6, 12, and 24 weeks. Overnight GH secretion was calculated by mathematical deconvolution of serial GH measurements from serum samples collected every 10 min (22:00-06:00) during simultaneous polysomnography in a subset of 18 men (active n = 11, sham n = 7) at week 12. Active, compared with sham, CPAP increased IGF-1 at 12 weeks (P = 0.006), but not at 6 weeks (P = 0.44). Changes in IGFBP-3 and IGFBP-1 were not different between groups at 6 or 12 weeks (all P ≥ 0.15). At week 24, there was a further increase in IGF-1 and a decrease in IGFBP-1 in the pooled group (P = 0.0001 and 0.046, respectively). In the subset, total (P = 0.001) and pulsatile (P = 0.002) GH secretion, mean GH concentration (P = 0.002), mass of GH secreted per pulse (P = 0.01) and pulse frequency (P = 0.04) were all higher after 12 weeks of CPAP compared with sham. Basal secretion, interpulse regularity, and GH regularity were not different between groups (all P > 0.11).
Conclusions: Twelve weeks, but not 6 weeks, of CPAP increases IGF-1, with a further increase after 24 weeks. Total and pulsatile GH secretion, secretory burst mass and pulse frequency are also increased by 12 weeks. CPAP improves specific elements of the GH/IGF-1 axis in a time-dependent manner.
Clinical trials registration: Australia New Zealand Clinical Trials Network, www.anzctr.org.au, number ACTRN12608000301369.
Keywords: Continuous positive airway pressure; IGF binding protein; growth hormone; insulin-like growth factor 1; obstructive sleep apnea; pulsatility.