Cardiovascular Risk Markers in Obstructive Sleep Apnoea Syndrome and Correlation with Obesity

Silke Ryan ¹, Geraldine Nolan ², Evelyn Hannigan ², Sean Cunningham ², Cormac T Taylor ³ and Walter T Mcnicholas ^4*

¹ St. Vincent's University Hospital, Republic of Ireland
² St Vincent's University Hospital, Republic of Ireland
³ University College Dublin, Republic of Ireland
⁴ St. Vincent's Hospital, Republic of Ireland

^* To whom correspondence should be addressed. E-mail: walter.mcnicholas{at}ucd.ie.

Accepted 26 November 2006

Abstract

Background: Elevated C-reactive protein (CRP) and homocysteine levels are risk factors for cardiovascular disease. Some, but not other, previous studies have reported increased levels of CRP and homocysteine in patients with obstructive sleep apnoea syndrome (OSAS). We investigated levels of these factors in carefully selected OSAS patient and matched normal control cohorts.

Methods: We measured CRP and homocysteine levels in 110 subjects following polysomnography (PSG). Non- OSAS patients [G1] were compared to two patient groups (mild/moderate [G2] and severe OSAS [G3]), group-matched for body mass index (BMI), and a fourth group of severe OSAS patients who were more obese [G4]. 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 therapy (CPAP) after PSG and 49 reassessed 6 weeks later.

Results: CRP levels were similar in all 3 BMI- matched groups (median[IQR] 1.11[0.76,2.11]mg/l [G1] vs 1.82[1.20,3.71] [G2] vs 2.20[1.16,3.59] [G3]; p=0.727 by Kruskal-Wallis testing) but significantly higher in G4 than in all other groups (5.36[2.42,9.17] mg/l, 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), whereas AHI and other measures of OSAS were not. There was no difference in homocysteine levels between all four groups (p=0.101). Furthermore, CPAP therapy did not alter CRP (2.29[1.32,4.10] vs 2.84[1.13,5.40] mg/l; p=0.145) or homocysteine levels (8.49±3.66µ mol/l vs 9.90±4.72µmol/l; p=0.381).

Conclusion: CRP and homocysteine levels were not associated with OSAS severity in men but CRP is independently associated with obesity.

Keywords: C - reactive protein, cardiovascular disease, homocysteine, obesity, obstructive sleep apnoea syndrome

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