Plasma homocysteine in obstructive sleep apnoea

Aims Whether increased homocysteine is one mechanism linking obstructive sleep apnoea (OSA) to cardiovascular abnormalities is unclear. We hypothesised that plasma homocysteine would be higher in OSA patients than in control subjects, would increase further during sleep, and decrease after treatment with continuous positive airway pressure (CPAP). Methods and Results For study A, homocysteine was measured in 22 OSA patients and 20 controls first before sleep, then after 5 h of untreated OSA, and then in the morning after CPAP treatment. Homocysteine was similar in the OSA and control subjects at all three time points, and declined overnight in both groups (P=0.0017, P=0.036, respectively). To further assess this diurnal variation, we studied plasma homocysteine under a full-night protocol in 10 OSA patients and 12 controls (study B). Homocysteine was measured before sleep, in the morning after sleep, and at noon. Results in both OSA and control groups showed an overnight decline in homocysteine which was reversed by noon (repeated measures ANOVA: OSA, P=0.04; controls, P=0.02). Study C showed that disturbed sleep did not affect homocysteine levels in normal subjects. Conclusion There is a significant diurnal variation in plasma homocysteine, so that homocysteine is lower in the morning after waking. Neither OSA nor disturbed sleep elicit acute or chronic changes in homocysteine.