What does this mean for me, the go-getter who brags to my friends about how much I work?
Stop doing that! It's annoying, and it won't pay off in the long run. If you're younger than 40, it may seem like a long way away, but it'll come sooner than you think -- and this study didn't make a conclusion one way or another for adults under 40, so more research is needed. The bottom line is that, if possible, find some work-life balance that gives you time to rest and recover away from the job.
Does this mean everyone will migrate to the three-day workweek? Tuesday will be the new hump day, Wednesday the new Friday. If four full days of sleeping in, lazy brunches, and Netflix binges mean we'll all be smarter, and better-equipped to live long, happy lives, then maybe it's time to change our culture. All in the name of science!