Read up on trademarks. This is MAYBE generic enough domain to be used for something else, but if you are making it about Apple's product you are going to be in trouble.
That is like Apple. If you want to register a domain with Apple in it to sell the apple fruit, nobody is going to say boo to you. But if you start a site with Apple in it and then start selling software or computers, then there is the chance your attempting to confuse the consumers into thinking you are actually Apple who is selling computers and iphones, etc.
I was thinking like Bros above and as you mentioned healthbook app, if developed, it could be claimed to infringe.