I don´t oil my blades regularly, just when I´m sure, I dont wanna use them for some time, but that´s personal taste (most of my knives are carbon steel blades). I wouldn´t use WD40, if you want to do food prep. I´d take mineral oil in general. It´s cheaper and it doesn´t matter when you eat an apple, peeled by a fresh oiled blade.
Just my two Cent.
Kind regards