SLP here. I get asked this a lot. I don't know of any particular studies that correlate sleep and stuttering levels, but here's what I always say: Sleep is required for pretty much all basic and complex body and brain functions. If you are underslept, you don't think as clearly, don't move as quickly, aren't as coordinated, *in general*. Speech is a motor activity that requires a lot of brain processing power. So it makes complete sense that less sleep --> less optimal speech functioning. Most people also tell me that they are more disfluent when they are sick. Same principle. If you're sick or underslept, *nothing* is working as well as it usually does. Speech follows that pattern! TL;DR For best results, ensure a good night's rest. /end unscientific entirely anecdotal "professional" opinion