Apple Said to Expand HealthKit From Tracker to Diagnosis Tool

So far Apple Inc.’s HealthKit has mostly collected fitness data from its devices. In the future, if the company gets its way, the software will interpret that information, turning it into advice for users, doctors and others.

Scores of health-care experts hired by Apple in recent years are building improved electronic health record software that can better analyze and understand the implications of patient data, according to people familiar with the team’s plans.

The iPhone maker is also working on new apps for the Apple Watch. One helps users track sleep patterns, one of the people said. Another app gauges ...