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Blood Oxygen Level and the Apple Watch Series 6

by Marianne Navada

One of the new health features in the Apple Watch (S6) is the ability to measure blood oxygen. Here’s what you need to know.

What Is Blood Oxygen Level?

Blood oxygen level is the amount of oxygen in the blood. It’s an indicator of how well our body distributes oxygen from the lungs to the cells, tissues, and organs. 

We also refer to blood oxygen level as oxygen saturation. 

What Is a Good Blood Oxygen Level? 

A normal blood oxygen level “is often considered between 90-100%”.  There are health and other external factors that can affect levels, such as being in high altitude or if you have an existing condition. The point: one can live a “normal life” with levels below “normal”, and one should always consult with a physician for a personal diagnosis.

Your doctor can provide recommendations as to what ranges of oxygen levels are acceptable for you.


How Do We Measure Blood Oxygen Level? 

The most accurate way to measure blood oxygen level is through a blood test. An alternative is a pulse oximeter, a device that one usually clips onto the tip of the finger. The Apple Watch works similarly to a pulse oximeter. The device shines infrared lights onto your wrist, which then measures the light reflected back. The color of your blood is an indicator of blood oxygen levels. “…bright red blood has more oxygen, while dark red blood has less”. 


Here are the criticisms:

– Smart watches that act as blood oximeters are not FDA approved and it’s questionable if the wrist is an ideal body part to measure blood oxygen levels.

– Apple does not provide an error rate, so we don’t know how much these readings are off by.

– It’s unclear how skin color affects results. 

The Washington Post

Similar to other health features of the watch, the watch oximeter is not meant to replace medical diagnosis nor are these apps considered medical devices. Rather, it’s a great way to monitor your body and overall wellbeing and provide professionals with detailed information about your health. 

Apple Watch: How it Works

The Apple Watch measures your blood oxygen level throughout the day when it detects optimal conditions to do so. You can turn off this feature by going to your Apple Watch Settings > Blood Oxygen Levels and change settings. Personally, I leave it on so I can get a sense of how my levels are throughout the day. 

If you decide to measure your blood oxygen level on your own, there will be moments when the watch is unsuccessful. Apple recommends: 

  • Resting your arm on a table or lap. 
  • The apple watch isn’t too loose or tight.
  • Watch is flush with the top of your wrist and away from wrist bone. 

On Your Phone 

You can check your aggregated data by going to the Health app > Browse > Respiratory > Blood Oxygen.

I find these graphs useful, since I know when my blood oxygen level goes down. I am finding a pattern in the time of day when they are high and low. Of course, I take these with caution given the limitations mentioned, but the fact that a pattern exists is something.

Currently, I don’t wear my watch to sleep, but I will start to, since I’m curious to know how my levels are during slumber. Blood oxygen levels usually go down during this time. 

Commit to living.