I dunno, sleep research is notoriously wishy washy. There are other studies that say living on ~5 hours of sleep a night will leave you with a longer lifespan. Ultimately, the takeaway is that we know abso-fucking-lutely nothing about sleep. Even when you go to take a sleep study and they wire you up, they just compare your brain activity to the average. They don't really know what is specifically going on; they have not deduced much aside from figuring out that your brain turns off most of your muscles when you sleep so you do not physically act out what you are doing in dreams, which would be disastrous. A defect in that mechanism is why sleepwalking happens.