Fitbit Estimated Oxygen Variation: We explain SpO2, sleep apnea and blood oxygen

We speak to Fitbit scientist about how it all works
Fitbit Estimated Oxygen Variation explained
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In January 2020 Fitbit turned on its long awaited blood oxygen detection feature. Since 2017 it's been packing an SpO2 sensor into its leading devices, but hasn't used the data. Until now.

Blood oxygen can be used to detect sleep conditions such as sleep apnea, and offer a better analysis of what's going on with our bodies in those lost hours.

But Fitbit's Estimated Oxygen Variation data needs a little explanation. We spoke to Dr. Conor Heneghan, Fitbit’s Lead Sleep Research Scientist for everything you need to know.

What is Estimated Oxygen Variation?

A reading of the oxygen levels in your blood, it uses a red LED in the optical heart rate monitor.

Fitbit's detection is a little different. Rather than spitting out a single percentage score it examines the difference in the highs and lows of your blood oxygen, and looks to highlight potential underlying conditions.

However, that would require you checking and understanding the data.

Fitbit devices with SpO2

Fitbit Estimated Oxygen Variation: SpO2, sleep apnea and blood oxygen explained

Fitbit has been packing SpO2 sensors into some of its wearables, so if you have a Charge 3, Fitbit Ionic or any Versa smartwatch you're good to go.

Users of Inspire or Alta trackers don't have the hardware inside, so won't get the update.

The new feature has been rolling out pretty fast, starting in the US and we've already had our devices updated.

Estimated Oxygen Variation Graph explained

Fitbit Estimated Oxygen Variation: SpO2, sleep apnea and blood oxygen explained

Unlike some devices that will give you a number for your blood oxygen level. However, a Fitbit spokesperson told us that the graph provided by Fitbit is an "estimation of the variability of oxygen levels in the bloodstream".

It's not a graph of the actual Sp02 estimate.

The example screenshot above shows what the graph will look like – and from what we can see, blood oxygen is monitored by the sensor during sleep – and variations which could show a sleep apnea issue are highlighted on the graph.

Essential reading: Fitbit's Sleep Score explained

"We're showing a metric which correlates with the average variability of your blood oxygen level," said Dr. Conor Heneghan.

"Let’s say Person A has oxygen level of 96% +/-1% and Person B has oxygen level of 95% +/- 4% throughout the night, then Person B will see a higher “estimated oxygen variation” throughout the night. We calculate this every minute."

Can Fitbit track sleep apnea?

Fitbit Estimated Oxygen Variation: SpO2, sleep apnea and blood oxygen explained

"We are not claiming this can be used to correlate with sleep apnea status," said said Dr. Conor Heneghan. "No, there is not currently an alert within the device or app. This graph is another opportunity for us to provide more data to our users."

So while a large level of variation in blood oxygen COULD show sleep apnea – Fitbit won't spell this out for you.

"Seeing frequent big variations is a clue that you may be experiencing breathing disturbances during sleep—something you might want to talk to your doctor about, particularly if you experience symptoms such as excessive tiredness, loud snoring, or gasping during sleep. Keep in mind that how you wear your device can also affect this data."

There's lots of caveats here, not least the "estimated" part of the Fitbit name. It's likely the company got fed up waiting for FDA clearance in the wake of competitors getting similar features out onto the wrists of consumers. So, for now, you need to check the data and make your own conclusions.

What else can Estimated Oxygen Variation Graph show?

Of course, blood oxygen isn't all about sleep apnea.
"Sleep apnea is a common cause of variation in oxygen level, but sleeping at altitude can also increase variability. It’s probable that some types of heart failure are associated with variation in oxygen level, too (Cheyne-Stokes respiration). However, we are not claiming any medical use with this feature," said Dr. Conor Heneghan.