“Snorers are three times more likely to suffer a potentially fatal blood clot,” the Daily Express has reported. The newspaper explains that researchers from Taiwan say this is the first study to prove that a link between sleep apnoea and deep vein thrombosis (DVT) exists.
Sleep apnoea is a particularly severe condition where sleep is disturbed by pauses in breathing as well as snoring. There are an estimated 3 million people in Britain who have sleep apnoea.
This seven-year study of more than 10,000 people - of whom about half had sleep apnoea - resulted in 40 cases of DVT. DVT is a serious but rare condition in which a blood clot forms in a vein - usually in the leg. The clot can break off and cause a life-threatening blockage in the lung, known as a pulmonary embolism.
Although the number of people developing a clot in this study was small (about 0.4%) the increased risk for people with sleep apnoea seems large when presented in relative terms (three times the risk). This presentation of the figures in the headlines could cause people to worry unduly.
There were 30 cases of DVT (0.53%) in the sleep apnoea (snoring) group and 10 (0.22 %) among the non-snorers after three to four years, which is an actual difference of 20 cases (0.31%). This means that if sleep apnoea was cured in 1,000 people then, "optimistically", about 3 cases of DVT could be prevented.
Limitations worth noting include:
- The study relied on administrative claims data recorded by physicians and non-clinical staff, which might make the diagnoses less accurate.
- Some personal information, including body mass index and smoking status, was not available, so the researchers were unable to fully adjust for these. Obesity is clearly linked to DVT and sleep apnoea and could have been an important confounder or alternative explanation for the effect seen.
“Sleep disordered breathing” and obstructive sleep apnoea are treatable conditions. Treating them is important as there are already several clear complications to having the condition, including:
- high blood pressure
- heart attacks
Snorers (or partners of snorers) can find out more about sleep apnoea.