The Heartline study, open to people aged 65 and older, will research atrial fibrillation and early detection of stroke using Apple's smartwatch.
The Apple Heart and Movement, Women's Health and Hearing Studies are now open for enrollment in the U.S.
The studies will be conducted in collaboration with leading medical institutions to examine hearing, women's, mobility and heart health.
The ResearchKit-based study launches in partnership with Stanford to identify irregular heart rhythms.
Called MyGeneRank, the app allows users with genetic data from 23andMe to obtain an estimated genetic risk score for coronary artery disease.
There is also a new video instruction step that makes it easier for developers to display rich video content to users within their apps.
BiAffect can monitor mobile device usage, including keyboard typing speed, to predict manic and depressive episodes in people with bipolar disorder.
The two parties aim to use digital health technology to help people with chronic pain decrease their use of pain medication.
The study will use WebMD's newly redesigned Pregnancy app for iPhone, enabling participants to easily answer questions and share connected device data.
Stress was the most common trigger, linked to 37% of seizures, followed by lack of sleep (18%), menstruation (12%) and overexertion (11%).