Health data that will soon be stored on iOS 8-powered devices could be a gold mine for ad networks, but Apple has made it off limits for now.

Ahead of Apple's expected September 9 new device launch, the company has set new rules for what developers can do with health data collected using its HealthKit platform — chiefly that they're not allowed to sell health data that could be used for targeted advertising.

HealthKit, available as part of iOS 8, offers developers a set of APIs to share their apps' data with Apple's new Health app, the iOS health hub where users can view data about their sleep, heart rate, calories burned, blood sugar, and cholesterol.

The Financial Times reported that an update to Apple's iOS developer program license agreement told developers that they must "not sell an end-user's health information collected through the HealthKit API to advertising platforms, data brokers or information resellers".

As noted by The Guardian, app developers using HealthKit can still share data with "third parties for medical research purposes" so long as they have the user's consent.

Apple's vision for the HealthKit is that it will allow users to share health data directly with doctors. The company has reportedly already been in discussions with healthcare professionals and also health insurers about how the platform could be used in the healthcare sector.

The company has also placed rules around what type of apps can use HealthKit data. Only apps that are "primarily designed to provide health and/or fitness services" will be able to use HealthKit APIs, according to The Guardian. Developers will also not be able to use HealthKit data for serving advertising themselves.

Of course, Apple's developer agreement don't prevent rogue developers from breaking the rules, however anyone serious about their app would risk being booted out of Apple's tightly curated App Store.

According to the FT, Apple execs have also discussed medical apps with the US Food and Drug administration, while others in the health tracking business, such as Fitbit, have recently clarified that they don't sell data that could identify the user.

Apple is expected to announce a new 4.7-inch display iPhone on September 9, and possibly an even larger 5.5-inch phone in addition to a new wearable that may be its long-rumored iWatch.

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