Ask HN: Improve your concentration?

Hi, I've noticed that my concentration tends to lapse after spending 12+ hours in front of a computer. At a startup thats a way of life so I want to find good ways to concentrate better and remain focused even while working long hours. So far, I've tried drinking a lot of water throughout the day, eating a lot of light meals, avoiding sugar. Also, I try to avoid multi-tasking. Its hard to avoid checking email because you always feel like you are missing something impt but thats an area where I definitley waste a lot of time.

Any efficiency gurus out there with any tips?