That being said this is no doubt a sensitive area as far as privacy is concerned since we reckon there are many who might object to their information being shared or used for the wrong reasons. This is why Apple has recently updated their guidelines which will now require such medical research apps that use ResearchKit to get approval from an ethics board.
According to the updated guidelines, “Apps conducting health-related human subject research must secure approval from an independent ethics review board. Proof of such approval must be provided upon request.” Prior to this, Apple had suggested to developers to consult with a review board or an ethics committee.
However with the updated guidelines, it seems that approval is a must and that Apple could ask to see proof of that whenever they want. Hopefully this will result in apps and researches that users will feel comfortable participating in.