#caffeine

"Coffee dehydrates you"
At normal intake, coffee's mild diuretic effect is offset by its own fluid volume — a controlled trial found no hydration difference between coffee and water drinkers.
Myth

Best Foods and Drinks for Focus
Most 'brain food' content is aesthetic. This is the actual evidence on caffeine, glucose, and attention.
Meta-analysis

Does Caffeine Affect Sleep? The Half-Life Problem
Caffeine's half-life is longer than most people plan around — here's the trial that measured a 6pm coffee's effect on sleep at midnight.
Single RCT