Compared with subjects within the lowest quartile of HDL-CH, the adjusted OR of pre-OSA and OSA in subjects within the highest quartile (>1.76 mmol/l) was 0.78 (95% CI: 0.65–0.94) and 0.59 (95% CI, 0.45–0.78), respectively; and a significant exposure-response trend was observed for both pre-OSA and OSA (both p < 0.05). Here, C4B is linked to obstructive sleep apnea syndrome.