BACKGROUND: Hypoxia-inducible factor 1 (HIF-1) affects the circadian clock in obstructive sleep apnea (OSA) and may have a bidirectional relationship with circadian mechanisms. This study examined the link between circadian clock and HIF-1 in OSA patients versus controls. METHODS: 70 participants underwent polysomnography (PSG), and were assigned into OSA (apnea-hypopnea index (AHI) ≥ 5, n = 54) or control (AHI <
5, n = 16) groups. RESULTS: The OSA group was characterized by increased CLOCK, CRY1, PER1 and HIF-1a protein levels, both in the morning and evening (all CONCLUSIONS: OSA affects the circadian clock and HIF-1 pathway, with increased CLOCK, CRY1, PER1, and HIF-1α protein levels observed in OSA patients. The interplay between these systems may involve complex posttranscriptional and posttranslational mechanisms.