I don't know how much of this I buy. I worked nights or 3rd shift for years by choice and I always felt just as sharp at night, if not sharper, as I did during the daytime once I got my sleep schedule sorted out.

If you're normally a daywalker and occasionally pull an all-nighter, sure I could see there might be some impact on your mental state. But once you flip the script, I don't see any reason for prolonged effect on your mental capacity. At least not in my experience.