New to iOS 8 is Apple's HealthKit platform, which offers the ability to track and share a vast range of health, fitness, and medical data points across multiple apps and devices. It can be used as a wellness and fitness tool--aggregating data about diet, activity, exercise, and sleep from multiple sources--as well as a serious medical tool for managing and monitoring chronic conditions.
It's a dynamic platform, working hard behind the scenes to deliver a personalized experience to each iPhone user, using data pulled from your iPhone's M7 or M8 sensor and allowing you to view all of this health data inside one app. Here's a quick guide to getting started and setting up your own health database.
Behind the scenes, yet always working
As a medical tool, HealthKit offers tremendous value for a few different reasons. It can aggregate data from a range of apps or connected medical devices, like a glucose meter or blood pressure cuff, as well as consumer-oriented fitness devices. It also offers the ability to automate the recording of medical metrics. If you're using connected devices, this helps to ensure the accuracy of the data because it goes straight from the device to the associated app on your iPhone and then into HealthKit. If your doctor's office uses an electronic records system that supports HealthKit, that data can then be automatically entered into your medical record.
For the most part, you don't interact with HealthKit directly. The platform is really little more than a data store on your iPhone, and apps can write information into and pull information out of it. Some apps do both, though others may only input data or retrieve it.
Most of the actual processing of HealthKit data--comparing the calories you've eaten with the number you've burned throughout the course of the day, getting data from a fitness tracker or other device, or compiling information and sending it to your doctor--is done in the third party apps that send information to and retrieve it from HealthKit.
Apple's Health app, which is pre-installed on any iPhone 4s or newer running iOS 8, is the exception to this rule. It provides you the ability to view all of your HealthKit data from every HealthKit-compatible app. It also allows you to manually enter data and includes a dashboard for visualizing the data.
Health also includes a Medical ID feature that allows you to record important medical information--conditions, medications, allergies, and emergency contacts (which can include your primary care doctor or specialists). You can choose to have your Medical ID available from your phone's lock screen in case of an emergency where you're unable to provide that information. You can access this by tapping the Emergency button when asked to enter a passcode, which also allows your iPhone to make 911 calls while locked.
Working with third-party apps
When you install an app that supports HealthKit, you'll need to configure it to access various types of HealthKit data. That process will vary from one app to the next, but typically the option to setup an app's connection with HealthKit is something you see the first time you launch an app or it's located within the app's settings. Most apps will also let you choose what metrics you want to record, access, or process--just switch on the appropriate toggles
When you configure an app to work with HealthKit data or if you later adjust which metrics it works with, you'll see a permissions screen called Health Access. The screen will identify the app and show you exactly which data points it will write into HealthKit and which ones it will read out of HealthKit. You need to explicitly confirm you are giving the app permission to access each individual data point both to write and read. This means that you know exactly what information an app can work with and ensures that apps cannot access data without your knowledge and consent.
You can see a full list of all the apps that have requested access to HealthKit both in Health (by tapping the Sources icon at the bottom of the app) and by selecting Health from the Privacy screen in Settings. You can also tap on each app to see what permissions it has requested and to change them.
Apple has built HealthKit to respect user privacy in part with the permissions model that allows you to always see what apps can access what data. It has also barred developers from selling HealthKit information to data brokers or mining it for any purpose other than medical research, in which case all the data must be made anonymous. If you backup your iPhone to your computer using iTunes, Apple requires you to enable the option to encrypt the backup in iTunes in order to backup your HealthKit data (if you don't, the data won't be included in the backup).
Even with these protections, however, it's wise to consider what an app is going to do with your data. For example, many fitness apps offer the ability to automatically post data to your social networks. Many services, including ones centered on weight loss, fitness, and healthcare store or process data in their own private clouds. What happens to information when you use such apps or services is governed by their terms of service, so pay extra close attention to what you're agreeing to when installing any health, fitness, or medical apps.