Cardiovascular risk markers in obstructive sleep apnoea syndrome and correlation with obesity

Background: High C- reactive protein ( CRP) and homocysteine levels are risk factors for cardiovascular disease. Some, but not all, previous studies have reported increased levels of CRP and homocysteine in patients with obstructive sleep apnoea syndrome ( OSAS). A study was undertaken to investigate the levels of these factors in carefully selected patients with OSAS and matched normal controls. Methods: CRP and homocysteine levels were measured in 110 subjects following polysomnography ( PSG). Non- OSAS patients ( group 1) were compared with two patient groups ( mild/ moderate OSAS ( group 2) and severe OSAS ( group 3)) group- matched for body mass index ( BMI), and a fourth group of patients with severe OSAS who were more obese ( group 4). All were free of other disease and similar in age, smoking habits and cholesterol levels. 50 suitable patients were commenced on continuous positive airway pressure ( CPAP) treatment after PSG and 49 were reassessed 6 weeks later. Results: CRP levels were similar in groups 1, 2 and 3 ( median ( interquartile range ( IQR)) 1.11 ( 0.76 - 2.11) mg/I vs 1.82 ( 1.20 - 3.71) mg/I vs 2.20 ( 1.16 - 3.59) mg/I; p = 0.727, Kruskal- Wallis test), but were significantly higher in group 4 than in the other groups ( 5.36 ( 2.42 - 9.17) mg/I, p < 0.05 by individual group comparisons). In multivariate analysis of all subjects, BMI was an independent predictor for CRP levels (beta = 0.221; p = 0.006) but apnoea-hypopnoea index and other measures of OSAS were not. There was no difference in homocysteine levels between all four groups ( p = 0.1). CPAP did not alter CRP ( 2.29 ( 1.32 - 4.10) vs 2.84 ( 1.13 - 5.40) mg/I; p = 0.145) or homocysteine levels ( 8.49 ( 3.66) vs 9.90 ( 4.72) mu mol/I; p = 0.381). Conclusion: CRP and homocysteine levels are not associated with OSAS severity in men but CRP is independently associated with obesity.