You’re counting your steps, tracking your workouts and measuring your sleep with your wearable fitness tracker. But these devices can do more than help you improve your health—the data they track can help you spot dangerous health problems. 

Just ask Curtis Carey of Hudson, Wisconsin. His wife gave him a Fitbit fitness tracker for Christmas 2017. After using the tracker for a few months, Carey, now 69, noticed his heartbeat was irregular. 

“It would jump up to 130 [beats per minute] then down to 60, then back up and back down,” he says. On the Fitbit app, he could see that his heart rate had been normal for the previous month or two.

He didn’t have any chest pain or discomfort, and a visit to his doctor didn’t uncover any problems.

But by fall 2018, Carey was worried. After strenuous activity, his heart rate would stay above 100 beats per minute for more than two hours. 

When a hunting trip left him winded and worn out, he sought care again. A CT scan of his heart showed blockages in three blood vessels, including one that was 95% obstructed. 

In March 2019 Carey had bypass surgery to clear the blockages and he’s now well into his recovery.

There are five serious health risks that your fitness tracker could help detect: heart disease, atrial fibrillation, kidney disease, diabetes, and cancer.

Heart rate irregularities could point to heart disease

Like in Carey’s case, the data from your fitness tracker could show an irregular heartbeat.

“Heart rate spikes that aren’t caused by exertion need to be explained.”
Felipe Lobelo
Emory University

Heart rate spikes that aren’t caused by exertion need to be explained, says Felipe Lobelo, an associate professor at the Rollins School of Public Health at Emory University in Atlanta. 

Any spikes accompanied by palpitations; pain in the chest, back, belly, jaw, or arm; lightheadedness; sleep issues; or shortness of breath warrant prompt medical attention. 

“Those are signs and symptoms typical of cardiovascular disease,” Lobelo says. “Whether they come with or without your Fitbit showing weird data, I think those are important things to check with your doctor.”

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Your tracker might also show a sustained increase in your typical resting heart rate. Most adults have a resting heart rate between 60 and 100 beats per minute, and lower numbers generally mean you’re more fit. 

Not sleeping enough, nicotine, caffeine and stress can raise your resting heart rate, but a resting heart rate that’s consistently well over your normal rate should prompt a call to your doctor, says Naresh Rao, director of physical therapy at Sports Medicine at Chelsea in New York City and a member of the American Osteopathic Association.

You’ll also want to watch how quickly your heart rate gets back to normal after exertion. That’s one of the most useful numbers you can get out of fitness trackers
Felipe Lobelo
Emory University

You’ll also want to watch how quickly your heart rate gets back to normal after exertion. That’s one of the most useful numbers you can get out of fitness trackers, Lobelo says. “The number of beats you can recover in the first minute is a pretty good marker of how fit you are,” he says. 

Early research is finding that if you exert yourself to 80 to 90% of your theoretical maximum heart rate (220 minus your age) that rate should drop by at least 25 beats per minute in the first minute of rest, Lobelo says. Lower recovery rates may mean you’re at higher risk for cardiovascular disease.

If your heart rate stays elevated for more than five to 10 minutes after exertion, that’s concerning, Rao says. In that case you should see your doctor or go to the emergency room.

The rhythm of your heart: detecting atrial fibrillation

The ECG feature on the Apple watch adds heart rhythm to the health features many wearables track. ECGs can help spot signs of atrial fibrillation, a rhythm disorder.

That information is useful, but Rao points out that the watch tracks one aspect of the heart’s rhythm, while medically supervised electrocardiograms track 12 different aspects.

Weight gain or loss could be a sign of kidney or heart disease, diabetes, or cancer

If you sync your wearable with a smart scale you can also watch for unexplained weight gain or loss. Unexplained weight gain could simply mean you’ve taken in more sodium than usual, and your body needs extra water to flush it out. 

But it could also be water retention from kidney disease or from congestive heart failure, where your heart is not pumping effectively. 

Weight loss when you’re not trying to lose weight could be a sign of various health conditions, including diabetes and cancer.

For sleep tracking, it may be too soon to spot problems

Rao isn’t sold on the sleep tracking features of wearables. He thinks it’s too early in their development to make meaningful decisions based on their data.

“The jury is still out on that,” he says. “They’re not measuring brain waves.” 

And for any health concerns, you won’t get all the information you need from a wearable device. “You typically need more than just a Fitbit. By themselves they are not going to diagnose anything. You need the combination of human touch and technology,” Lobelo says. “But they can provide useful insights for diagnosis and help people achieve an active lifestyle.”

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