The devices are just one part of the study. Participants will also receive at-home gene and microbiome sample kits from UBiome that will help find any common genetic traits. They'll also have to spend about 10 minutes per day logging their diets, goals and moods in a mobile journaling app, Recovery Record.

While you don't strictly need an Apple Watch to track heart information, not every device has the ability to provide detailed heart rate histories or share data directly with researchers. That makes it particularly useful for studies like this, and gives Apple a potential edge over rivals. It's hoping to extend that tracking further when it enables ECGs on Series 4 watches in the near future.