SAN FRANCISCO (KPIX 5) — The heart rate sensors in the most popular wearables tech, including the Apple Watch and Fitbit, might not work as well for people of color, according to an article published in STAT, a health and medicine publication.

Some users have complained about inaccurate readings from Fitbit on Reddit.

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CNET News Editor-at-Large Ian Sherr says this problem has persisted for a long time, but the technology is getting better.

“The way it works is that they use a green light that then tracks when there is more blood or less blood. And what they do is they actually have increased the amount of light that they’re using,” said Sherr. “Apple actually uses infrared on top of all of that.”

The STAT report says that green light is more readily absorbed by melanin, which is a natural skin pigment more prevalent in people with darker skin.

“Scientific studies, any type of study on humans, usually they’re done with the majority, which is typically white people. So when people of color have the same issues that the scientific study is testing, then you’re not really going to see what’s really going to affect them,” said San Francisco resident Bakari Adams.

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Fitbit said in a statement to KPIX 5:

“Fitbit takes accuracy very seriously and continuously performs studies to rigorously test the accuracy of our products among diverse groups of users. Our internal studies show that Fitbit’s PurePulse technology performs to industry standard expectations for optical heart rate on the wrist, tested against properly calibrated industry standard devices like an EKG chest strap. To achieve the most consistent performance, we specifically designed our optical system to emit green light at sufficient strength to effectively penetrate darker skin and our detector to be sensitive enough to accurately detect the heart rate signal. Our R&D team carefully evaluates other technologies, including infrared light, which we have found performs less well in ascertaining heart rate signal, particularly during motion.”

Graduate student Tevon Strand-Brown says tech companies may not have considered biases as they grew rapidly.

“I think it’s something that needs to start happening not just in tech companies, but from my perspective, engineering education. It’s something that Stanford hasn’t really done in the past but could do a lot more of in the future,” he said.

Experts say it’s important to note that these devices are designed to help users better understand their health, but should not be a replacement for going to see a doctor or used as a medical grade device.

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KPIX 5 has reached out to Apple for comment, but have not yet heard back.