Can a Fitbit or Apple Watch Help Fight Thyroid Disease?

A nursing student recently used a TikTok video that went viral to share how she believed that her Apple Watch could have helped diagnose her thyroid condition. Noting that such wearable devices can track oxygen levels, heart rate, presence of irregular heartbeats, and VO2 max, she explained her belief that if she had the notifications on, these might have pointed to an issue with her thyroid. She was subsequently diagnosed with hypothyroidism.

Anand Narayanan, MD

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

These devices use plethysmography to measure heart rate, heart rhythm (normal sinus rhythm vs atrial fibrillation), blood oxygen saturation, and VO2 max (maximal oxygen uptake as a surrogate for cardio fitness).

Wearables Accurate for Tracking Heart Rate

Numerous studies have demonstrated the accuracy of heart rate data from wearable devices when compared with conventional measurement, even though there is minor variability between smartwatch brands.

Aaron Neinstein, MD

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

One study revealed that wearable device heart rates could correlate well with patients' thyroid disease state. This study looked at 30 patients with hypothyroid and 14 patients with euthyroid in the setting of receiving radioactive iodine therapy for thyroid cancer. They found that a decrease of Fitbit heart rate by 1 standard deviation was associated with a 0.2 ng/dL decrease in free thyroxine levels and a twofold increase in the odds ratio of hypothyroidism. Heart rate measured by wearable devices showed better sensitivity than resting heart rate measured in the office setting owing to higher volume and frequency of data collected.

So we believe that in the near future, physicians will commonly prescribe a wearable wrist device alongside measurement of thyroid function tests to support management of patients' thyroid disease.

Rise in Telemedicine May Prompt More Use of Wearable Device Data

Also, with the increase in telemedicine prompted by the COVID-19 pandemic and some people preferring remote visits, we believe that wearable devices will further enable a shift in care towards reliance on data points obtained from wearables to inform our patient care.

We have seen it first-hand with a recent patient, Mrs B, who was admitted to the hospital with atrial fibrillation with rapid ventricular response. We diagnosed her with Graves disease and discharged her on methimazole.

During her post-discharge telehealth appointment, she described heart rates from her Fitbit that had dropped to between 40 and 60 beats/min. Using this information and her thyroid function tests, we were able to have confidence in decreasing her methimazole dose remotely.

Because she had only nonspecific symptoms, we leveraged her heart rate trends as an objective way to monitor her condition. This left Mrs B confident that her Graves disease was being treated appropriately.

We have previously published other reports about similar cases where wearables showing heart rate aided in diagnostics and treatment of thyroid disease.

VO2 Max Needs More Validation

In the last decade, wearable wrist technology has become widely adopted. We are increasingly likely to have patients with known or undiagnosed thyroid disease using smartwatches, thus giving them the opportunity for greater insights into their health from something already on their wrist. Certain metrics, such as heart rate and rhythm, have been extensively researched and validated, whereas other metrics remain more hope than reality. Over time, other and more metrics and data from these devices may provide greater visibility into pathophysiology than is possible today.

We imagine a future where metrics such as VO2 max or energy expenditure from wearable devices could provide more useful information for thyroid disease management.

For now, wearable technology enables us to better practice telehealth and leverage continuous heart rate data in conjunction with patients' reported symptoms to better enable accurate remote assessments of thyroid function.

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Cite this: Anand Narayanan, Aaron Neinstein. Can a Fitbit or Apple Watch Help Fight Thyroid Disease? - Medscape - Jul 21, 2022.