Apple Health study reveals important data on the menstrual cycle

In honor of International Women’s Day, new preliminary findings from the Apple Women’s Health Study underscore the importance of paying attention to menstrual cycles and their connection to overall health.

Many doctors consider periods to be a vital sign, but this area of health is under-researched. The Apple Women’s Health Study is the first of its kind research conducted with the Harvard TH Chan School of Public Health and the National Institute of Environmental Health Sciences (NIEHS) that aims to advance understanding of cycles periods and how they relate to various health conditions, such as polycystic ovary syndrome (PCOS), infertility, and the menopausal transition.

The study is significant in its scope and scale because it invites anyone in the US who has ever menstruated to contribute to this research simply by using their iPhone.

new findings

Researchers at the Harvard Chan School used survey data from the Apple Women’s Health Study to advance scientific understanding of the relationship between persistent abnormal periods, PCOS and endometrial hyperplasia, and cancer. Looking at a preliminary analysis cohort of more than 50,000 study participants, the study team found:

12 percent of the participants reported a PCOS diagnosis. Participants with PCOS had more than four times the risk of endometrial hyperplasia (pre-cancer of the uterus) and more than 2.5 times the risk of cancer of the uterus.

5.7 percent of participants reported that their cycles took five years or more to reach cycle regularity after their first period. Participants in that group had more than double the risk of endometrial hyperplasia and more than 3.5 times the risk of uterine cancer, compared with those who reported that their cycles took less than a year to reach regularity.

“More awareness is needed about the physiology of the menstrual cycle and the impact of irregular periods and PCOS on uterine health,” said Shruthi Mahalingaiah, MD, MS, assistant professor of Environmental Reproduction and Women’s Health at Harvard Chan School and Co-Principal Investigator of the Apple Women’s Health Study.

Cycle Tracking on iPhone and Apple Watch

The Apple Women’s Health Study invites anyone in the US who has ever menstruated to contribute to scientific research by signing up through the Apple Research app.

The study allows participants to share their cycle tracking data, along with other health data from their iPhone and Apple Watch, if they have one. Participants can also provide a more complete set of information about their personal and family history and lifestyle through occasional surveys.

Those interested can download the Apple Research app to enroll in the Apple Women’s Health Study./Courtesy Apple

The Research app helps the study reach people at various stages of their lives, different races, and across the United States. Participants control the types of data shared with the study, with transparency about how the data will be used for study purposes.

Cycle Tracking is available in the Health app on the iPhone or the Cycle Tracking app on the Apple Watch, allowing users to track their menstrual cycle along with details such as symptoms or ovulation test results. Cycle Tracking uses information users have recorded for past periods and cycle length, plus heart rate data from Apple Watch, to provide predictions of fertile periods and windows. Users can turn on notifications to let them know when their next period or fertile window is approaching.

With iOS 16 and watchOS 9, Cycle Tracking can inform users if their recorded cycle history from the previous six months shows a pattern of irregular periods, infrequent periods, prolonged periods, or persistent spotting. It’s important to know when these patterns occur, as they may be a sign of an underlying health condition. Users can also get information about the detected cycle deviation and export the last 12 months of their cycle history in PDF format to share with their supplier.

Additionally, new temperature detection capabilities in Apple Watch Series 8 and Apple Watch Ultra allow users to receive retrospective ovulation estimates. The new sensors collect overnight wrist temperature data that can be used to estimate the probable day of ovulation after it has occurred and improve period predictions. Knowing when ovulation occurred can be helpful for family planning, and users can view these estimates in the Health app.

Cycle Tracking allows users to conveniently track their menstrual cycle and receive period and fertile window predictions./Courtesy Apple

Privacy is fundamental to the design and development of all Apple features. When a user’s iPhone is locked with a passcode, Touch ID, or Face ID, all their health and fitness data in the Health app, except Medical ID, is encrypted.

All health data backed up to iCloud is encrypted both in transit and on Apple’s servers. When using iOS and watchOS with default two-factor authentication and a passcode, the Health app data synced to iCloud is end-to-end encrypted, which means Apple doesn’t have the key to decrypt the data and therefore therefore, you cannot read them.