It goes without saying that the HealthKit data collected by different apps in iOS 8 is private and can only be shared or used by the iPhone owner and their approved doctor or insurance company. However, Apple wants to make sure that there will be no privacy issues, so they've just tightened the rules in that regard.
According to The Guardian, Apple has changed the rules of the game in their latest iOS 8 Beta. The tech giant has advised developers that their apps are not allowed to use the info provided by HealthKit in order to make money off it. There will be no bulk info sales to advertisers, data brokers or information resellers.
However, data may be shared with third-party medical facilities for research purposes. Also, the developers are not allowed to have their apps access the info from HealthKit unless they are built specifically for fitness services or are linked to an external device like a bracelet, fitness band or other accessories.