Obstructive Sleep Apnoea (OSA) is associated with a high prevalence of hyperuricaemia, which occurs in up to 57% of men with severe OSA, most likely due to increased oxidative stress. Previous work has shown that treatment of OSA with Continuous Positive Airway Pressure (CPAP) reduces serum and urinary uric acid levels, but these studies have been conducted without appropriate control groups. We aimed to assess this effect in a randomised controlled trial.
Stored serum samples from a previously described trial group were analysed (1). This consisted of samples taken from 38 men with known type 2 diabetes and newly diagnosed OSA (>10 dips/h >4% in oxygen saturation (ODI)), randomised to receive either therapeutic (n=19) or placebo CPAP (n=19) for 3 months. Serum Uric Acid (SUA) levels were measured from samples taken at baseline and after 3 months CPAP.
Results are expressed as mean (SD). Both groups were well matched at baseline, with no significant difference between age 58.1 years (10.6) therapeutic CPAP group vs. 55.6 (6.9) placebo CPAP group, BMI 36.4 kg/m2 (5.0) vs. 35.6 (3.6), HbA1c 8.5% (1.8) vs. 8.1% (1.6), or ODI 33.9/hour (21.9) vs. 35.7/hour (21.1). There was also no significant difference in therapeutic or placebo CPAP usage 3.7h/night (3.2) vs. 3.7 (2.6) p=0.8. There was no significant difference in SUA levels at baseline 362 µmol/l (96) vs. 413 µmol/l (91), or at 3 months 354 µmol/l (83) vs. 406 µmol/l (101). Baseline SUA did not correlate with Apnoea-Hypopnoea Index (r=–0.2, p=0.5), ODI (r=0.1, p=0.6), BMI (r=0.1, p=0.4), or HbA1c (r=–0.3, p=0.9). The mean change in SUA at 3 months did not differ significantly between treatment groups (–7.6 µmol/l (35.9) vs. –6.2 µmol/l (46.2); p=0.9, 95% CI –28.7 to 25.9).
This RCT using therapeutic and placebo CPAP has shown no evidence of a significant reduction in serum uric acid following three months treatment. This is in contrast to previously published uncontrolled data. This study was not however powered to detect a difference in SUA levels and may be therefore underpowered. Further RCTs are needed to explore this effect further.
West SD, et al. Thorax. 2007; 62:969–974.