Can a Fitbit or Apple Watch Help Fight Thyroid Disease?

A nursing student recently used the viral TikTok video to share how she thought her Apple Watch could help diagnose her thyroid condition. Noting that such wearables can track oxygen levels, heart rate, an irregular heartbeat, and VO2 max, she explained her belief that if it had the notifications, it might indicate a thyroid problem. She was later diagnosed with hypothyroidism.

Anand Narayanan, MD

Stories of people identifying potential health abnormalities via consumer wearables are becoming popular as users increasingly have wearable devices capable of passively tracking health information, such as the Apple Watch or Fitbit, on their wrist. A June 2019 Pew Research Center survey showed that by that time, 21% of US adults regularly wore a smartwatch or fitness tracker.

These devices use plethysmography to measure heart rate, heart rhythm (normal sinus rhythm versus atrial fibrillation), blood oxygen saturation, and VO2 max (maximum oxygen uptake as a proxy for heart health).

Precise wearable devices to track your heart rate

Several studies have shown the accuracy of heart rate data from wearables when compared to traditional measurement, although there is slight discrepancy between smartwatch brands.

Aaron Neinstein, MD

Regarding heart rhythm, a large trial was published in The New England Journal of MedicineThe Apple Heart Study recruited 419,297 patients and found a positive predictive value of 84% between irregular heartbeat notifications on the Apple Watch and a diagnosis of atrial fibrillation.

One study revealed that the heart rates of wearable devices can correlate well with patients’ thyroid disease status. This study looked at 30 patients with hypothyroidism and 14 patients with hypothyroidism in a setting receiving radioiodine treatment for thyroid cancer. They found that a decrease in a Fitbit heart rate of 1 standard deviation was associated with a 0.2 ng/dL decrease in thyroid hormone levels and a twofold increase in the odds ratio for hypothyroidism. Heart rate measured by wearable devices showed better sensitivity than resting heart rate measured in an office environment due to the higher volume and frequency of data collected.

So we believe that in the near future, clinicians will typically prescribe a wrist device that can be worn along with measuring thyroid function tests to support the management of patients’ thyroid disease.

Rise in telemedicine may lead to more wearable data usage

Also, with the increase in telemedicine driven by the COVID-19 pandemic and some people favoring remote visits, we believe that wearables will allow a further shift in care towards relying on data points obtained from wearables to inform our patient care.

We saw this firsthand with a recent patient, Mrs B, who was hospitalized for atrial fibrillation with rapid ventricular response. We diagnosed her with Graves’ disease and gave her methimazole.

During her telehealth appointment after hospital discharge, she described her Fitbit’s heart rates which dropped to between 40 and 60 beats/minute. Using this information and thyroid function tests, we were able to be confident in reducing the dose of methimazole remotely.

Since she only had nonspecific symptoms, we took advantage of her heart rate trends as an objective way to monitor her condition. This made Mrs. B confident that her Graves’ disease was being treated appropriately.

We’ve previously published other reports of similar cases where wearable devices that monitor heart rate help diagnose and treat thyroid disease.

VO2 Max needs further verification

In the last decade, wearable wrist technology has become widespread. We are increasingly likely to have patients with known or undiagnosed thyroid disease using smartwatches, which gives them the opportunity to gain greater insights into their health from something already on their wrist. Extensive research has been done and validation of certain metrics, such as heart rate and cadence, while others remain more hopeful than reality. Over time, measures and other data from these devices may provide greater insight into pathophysiology than is possible today.

We envision a future in which measures such as VO2 max or energy expenditure from wearable devices can provide more useful information for managing thyroid disease.

Currently, wearable technology enables us to better practice telehealth and leverage continuous heart rate data along with patients’ reported symptoms to enable accurate remote assessments of thyroid function.

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