Sleep apnoea, snoring and CVD: still the causal link is missing

Both sleep apnoea and snoring have been included as risk factors for CVD, mainly from observational studies, however the biological pathway of causality remains unknown. To explore the mechanism would improve therapeutic intervention of sleep apnoea, even more the prevention of CVD.

In the present study (1) the method was applied in such a way to rule out possible confounders and reverse causality, based on the genetic variants of sleep apnoea and snoring reported in recent large studies (2). Genetic associations, aiming to investigate bidirected causality of sleep apnoea and snoring with common CVD i.e., hypertension, coronary artery disease, atrial fibrillation, heart failure and stroke were obtained from 5 cohorts from the UK, Canada, Australia, USA and Finland, using multivariate Mendelian randomization, adjusted for Body Mass Index (BMI), smoking, education and insomnia. The interesting finding of the analysis of 523366 samples showing sleep apnoea and snoring both having significant correlations with hypertension and coronary artery disease, attenuated after adjustment for BMI as a confounder. The associations with the rest of cardiovascular morbidity were not significant. Similarly, only hypertension was linked to the occurrence of sleep apnoea, increasing the risk by 53%, but this causal effect decreased to unsignificant values after multiple testing. In simple words, patients who snored or experienced sleep apnoea tend to have increased risk for CVD, if they also have increased BMI.

Considering the associations between snoring and sleep apnoea with cardiovascular diseases, the results indicate a genetic pathway that also include obesity. Obesity and sleep apnoea often co-exist, moreover they share common genes and common metabolism mechanisms, which according to the present study could partially explain their association with CVD. For the clinical practice implementation, it is even stronger to recommend for prevention and management of CVD intensive weight control for patients who snore or are being diagnosed with sleep apnoea, mainly for those with hypertension or coronary artery disease. Still, the critical question remains: which came first, the chicken or the egg?