Driving is a skill requiring many simultaneous cerebral activities, mainly eye-hand coordination with accurate speed and direction computations.1 This high level of activity requires full concentration, as evidenced by the higher accident rates in those who use mobile phones while driving.2 There is very good evidence that inadequate sleep is an important cause of fatigue-related driving accidents, possibly causing up to 20% of all accidents.3 Most of these sleep-related accidents are due to lifestyle issues such as driving without having had adequate sleep, and happen at times when vigilance is naturally low (eg, in the afternoon and at night).3 Furthermore, accidents are extremely expensive to society, with fatal accidents costing over £1 million.4 For nearly 20 years the part played by sleep disorders—particularly obstructive sleep apnoea (OSA)—has been recognised.5 OSA can grossly fragment sleep and produces excessive daytime sleepiness that is likely to cause the increased road traffic accident rates seen in patients with OSA. However, it is not entirely clear what aspects of sleep fragmentation in OSA lead to poorer driving ability: is it just sleepiness and inevitable “microsleeps” at the wheel or is there also general impairment of driving skills including eye-hand coordination such as occurs with excess alcohol? The evidence suggests mixed effects during simulated driving.6

As with arguments over OSA and cardiovascular risk,7 there may be confounders influencing any apparent relationship between OSA and driving accidents. For example, obesity itself is a cause of excessive sleepiness without necessarily the presence of OSA.8 Obesity may influence mechanical aspects of driver ability such as proper scanning of the road (particularly to the sides), as well as fully effective braking and steering in hazardous situations. Other risk factors for OSA such as alcohol consumption may also be important confounders. In …