The future of public health could be in your hands – or on your wrist, to be precise.

Researchers are using smartwatches and fitness trackers to do rigorous large-scale studies that would have been impossible in the past. It’s a growing trend that may vastly expand our knowledge of an array diseases.

“There’s really no disease that won’t be touched by this type of research,” said Calum MacRae, MD, PhD, vice chair of scientific innovation for the Department of Medicine at Brigham and Women’s Hospital.

Wearables are already in use to research heart, respiratory, neurological, and liver diseases, as well as gynecological conditions, certain cancers, diabetes, sleep quality, autism, and mental illness. In one recent example, as many as 1 million iPhone and smartwatch users may sign up to share data about their menstrual cycles and other health and lifestyle factors like sleep and stress. Already, 100,000 have enrolled in this Apple Women’s Health Study, a 10-year project among Harvard, Apple, and the National Institute of Environmental Health Sciences (NIEHS) that is unprecedented in size and scope.

There are a lot of mistaken beliefs out there about clinical trials, but they may actually be the key to treating cancer. Doctors know that an irregular menstrual cycle can be a sign of many things, from infertility to heart disease, diabetes, or even cancer. Many doctors believe menstrual history should be considered a vital sign, like pulse or blood pressure, but they say menstrual and reproductive health is woefully underfunded and understudied.