As you noticed in your example, it is often used about about abstract things. Yes, one might say, "you need a healthy dose of vitamins, etc." But it is also common to say, "She needs a healthy dose of realism," etc.

Hey! So it basically means a good amount or a lot, not to go lightly on something... if that makes sense. So if someone says “I need a healthy does of sun” that means they need a lot. In your example it implies that many people think jealous is bad but in fact some (or a healthy dose) is good. There is no specific amount someone means when they say this and depending on the context it can mean some or a lot. I hope I could help!