HealthKit

HealthKit is Apple's software framework for managing health and fitness data. Introduced with iOS 8, it provides a central, secure repository for health data and a set of APIs that allow apps to read and write this data with the user's consent. By standardizing data types and storage, HealthKit enables different health and wellness apps to share information and create a more coherent view of a user’s health.

HealthKit supports a range of data types, including quantitative metrics such as steps, distance, active and basal energy burn; vitals like heart rate and blood pressure; and long-term measurements such as height, weight, body mass index, sleep analysis, and glucose. The data is stored in a local database on the device and can be collected from multiple apps or devices. Developers must request explicit authorization for each data type the app wishes to read or write.

Privacy and security are central to HealthKit. Access to data requires user consent, and data can be protected with device passcodes and encryption. Health data can be backed up and, if enabled, can be synced with iCloud with user-controlled privacy settings.

Apple's Health app provides a user interface to view, annotate, and export HealthKit data and to control which apps have access. Third-party apps can integrate with HealthKit to contribute to or consume health data, enabling use cases such as activity tracking, chronic disease management, and clinical research.

Limitations include variability in data accuracy and the need for user consent for data sharing. HealthKit remains a foundational tool for iOS health apps, emphasizing privacy, interoperability, and user control.