For the women's health study, the company's teaming up with the Harvard T.H. Chan School of Public Health and the NIH's National Institute of Environmental Health Sciences. The study "seeks to analyze the impact of certain behaviors and habits on a wide breadth of reproductive health topics," Apple said.

It'll look at menstrual cycle data and ask participants for more details with monthly surveys, in the hopes of gaining deeper understanding about conditions such as polycystic ovary syndrome (PCOS), infertility, osteoporosis and menopausal transition. Apple says the multi-year study is the first long-term one "of this scale and scope."

Apple's partnering with Brigham and Women's Hospital and the American Heart Association for its heart and movement study, which will explore factors that impact heart health and "potentially cause deterioration in mobility or overall well-being." Participants can take sign up through the Research app and track their workouts with Apple Watch. The study may provide insights on how "certain mobility signals and details about heart rate and rhythm could serve as potential early warning signs of atrial fibrillation (AFib), heart disease or declining mobility."

The third study will collect headphone usage and environmental sound data via iPhone and the Apple Watch Noise app to look at how they affect hearing over time. It'll also explore how sound exposure over time can affect cardiovascular health and stress levels. Apple's working with the University of Michigan on that project, data from which it'll share with the World Health Organization's Make Listening Safe initiative.

Apple says the Research app will only share data with studies you've signed up for. The app explains how your data will be used, and you can control what information you share with each research team. Apple customers in the US can download the app and join the studies as of today.