TFF2 and obstructive sleep apnea syndrome: Spearman rank correlation analysis showed that in the MetS with OSAHS group, lgC5 was negatively correlated with the AHI (r = − 0.394, P = 0.035, Fig. 3) and was not correlated with triglycerides, HDL-C, fasting blood glucose, bradykinin, CGRP, SP, pepsin, IL-8 and other indicators.