Speaking from experience & research;
Reading not only boosts your brainpower, but also has other side-effects. First and foremost, it is the number 1 positive escape, it relaxes you, passes time, and gives you an overwhelming sense of joy! (depending on the type of reader). Drugs are a negative escape, reading is a positive escape; that is where it comes from. Reading is said to "increase intelligence", but that's only if you read non-fiction (I'm a fiction book worm), but reading any book can boost your memory.
Have a nice day!
(if it wasn't clear enough or if you would like me to elaborate/explain then simply comment below!)
Cheers,