FGF23 and obstructive sleep apnea syndrome: After adjustment for age, BMI, diabetes, hypertension, asthma, thyroid disease, COPD and vitamin D levels, α-Klotho levels were lower in the severe and non-severe OSA group (<i>p</i> = 0.001, both) compared to the simple snoring group, whereas FGF-23 levels were higher in the severe and non-severe OSA group (<i>p</i> = 0.001; both) compared to the simple snoring group.