"Jak jest twoje zdrowie?" sounds totally wrong to me, although I understand perfectly why you wrote that. It's hard to say if there is some verb implicit here. I guess you should just remember this as a construction which is a bit ungrammatical.
"Jak twoje zdrowie?" isn't some superidiomatic phrase like "How are you?"... I think the literal translation of "How is your health?" is equally natural and equally weird at the same time ;)