As always, take these things with a pinch of salt.  Though the comments are quite interesting and useful to read.

As a family we have definitely put more emphasis on good sleep routine, more exercise and less screen time.  Harder to do so with our now teens, but we believe it is the best approach for our younger ones.

At least 60 minutes of physical activity a day, nine to 11 hours of sleep a night, and no more than two hours a day of recreational screen time were tied to higher mental test scores.

NYTimes: 
https://www.nytimes.com/2018/09/26/well/mind/kids-brainpower-tied-to-exercise-sleep-and-limited-screen-time.html