In mid-2015, researchers studying fitness trackers counted 500 different devices on the market. They ended up having 60 participants, including the lead researcher, wear up to 7 devices every day for as long as 11 months, and then analyzed the more than two million data points they'd collected. Reporting in the journal PLoS Biology, they say that while "portable biosensors" are marketed as fitness trackers, they can also establish one's baseline health, revealing "useful health information" ranging from personal circadian rhythms and environmental changes to very early signs of illness or disease. In other words, looped in with one's medical records, these devices could help improve preventative care.
The lead researcher, geneticist Michael Snyder, had in 2012 learned through genetic analysis that he was at risk of developing diabetes in spite of his healthy lifestyle, he reported in the journal Cell; with the multiple trackers on his wrist, he was able to track his own insulin sensitivity. He even once noticed his oxygen level, which generally dips on airplane flights, fail to return to normal when he landed in Norway. Then a mild fever set in, and he ended up being diagnosed with Lyme disease at a very early stage. "What we really want to understand is what does it mean to define a healthy state, then quickly identify deviations from that state," he tells Scientific American. He compares the effect to a car's check engine light, and adds: "It's nice to see a little light when something's not right." So which trackers do this best? That's next on Snyder's list to study. (One woman found out she was pregnant thanks to her Fitbit.)