Decreased fat oxidation during exercise in severe obstructive sleep apnoea syndrome.

Aim: To assess whether the severity of obstructive sleep apnoea syndrome (OSAS) is associated with altered fat oxidation (FO) during physical exercise in men with type 2 diabetes (T2DM) and/or the metabolic syndrome (MetS).

Methods: A total of 105 consecutive overweight or/and T2DM male patients were hospitalized for metabolic check-ups including bioimpedancemetry to measure lean body mass (LBM), standardized exercise calorimetry to assess FO, maximum fat oxidation (MFO) and carbohydrate oxidation (CHO), and OSAS screening using respiratory polygraphy. Twenty patients were classified as having severe OSAS, according to the apnoea/hypopnoea index (AHI), with greater than 30 events/h (mean AHI: 45.2±14.3 events/h). They were group-matched for age, BMI, and the presence of T2DM and/or MetS with two other OSAS groups: mild (AHI<15 events/h [n=20]; mean AHI: 8.8±4.5 events/h); and moderate (AHI>15 events/h and<30 events/h [n=20]; mean AHI: 23.7±4.2 events/h).

Results: MFO adjusted for LBM was severely decreased in the severe OSAS group (1.6±1.0 mg.min(-1).kgLM(-1)) compared with the moderate (2.5±0.9 mg.min(-1).kgLM(-1); P=0.008) and mild (2.9±0.8 mg.min(-1).kgLM(-1); P=0.003) groups. All exercise-intensity levels (20%, 30%, 40% and 60% of the theoretical maximum aerobic power) showed reduced FO levels between the severe and mild-to-moderate OSAS groups. However, no differences in CHO were seen at any level of exercise between groups. Pearson's correlation analysis showed that AHI and the oxygen desaturation index were negatively associated with MFO corrected for LBM (r=0.41 and r=0.37, respectively; P<0.005).

Conclusion: OSAS severity is associated with altered FO during exercise.