Can your fitness tracker spot illness before you can?

In just a few years fitness trackers and wearable health monitors have gone from novelty to trendy. Now research suggests body sensors can do much more than count your steps.

Trackers can give insight into your baseline health and signal changes that could help your doctor, according to a new study from the Stanford University School of Medicine.

Researchers used bio sensors to track more than 250,000 daily health measurements from 60 study participants over two years. They tracked participants’ weight, heart rate, blood oxygen, skin temperature, and calories in and out. They also measured people’s exposure to gamma rays and X-rays in their bones to discover whether doctors could catch signs of illness before the wearer felt symptoms.

It was possible, researchers concluded, to measure deviations from normal and to associate them with environmental conditions, illness or other factors that affect health.

Geneticist Michael Snyder, one of the study’s senior authors, wore eight sensors on a flight to Norway in 2015 and noted changes in his heart rate and blood-oxygen levels. From previous trips, he knew his oxygen levels usually dropped during airplane flights and his heart rate increased at the start of the flight but both eventually returned to normal. That didn’t happen on the Norway flight.

Snyder says he wasn’t surprised when he later developed a fever and signs of Lyme disease, which were confirmed by subsequent tests. “Wearables helped make the initial diagnosis,” Snyder said in a news release.

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