Why is で used in 健康でいられる but not に？ Is this an adverb?

Question

I'm really confused about this one, does it mean "Stay healthy"? But if it does mean that shouldn't it be に instead of で？

Answer 1

健康 is a na-adjective, and ～でいる is the correct way to say "to stay [state]". でいられる is its potential form.

• What is the difference between でいる and である in this example?
• What is the meaning/grammar behind noun + でいる?
• ～ないでいる verb ending

健康でいられる
to be able to stay healthy

～にいる means "to be at/in [place]" (e.g., 日本にいる = "to be in Japan"), but 健康 is not a place.