Reference charts
Normal Oxygen Level While Sleeping (SpO2)
Blood oxygen dips a little during sleep. The usual reference for how far it goes in healthy people is an all-night pulse oximetry review of 350 people whose sleep studies were normal (Gries and Brooks, Chest, 1996). This page reads those numbers. Whether a watch or ring measures them accurately at night is a separate question.
Updated . Educational reference, not medical advice.
What is a normal oxygen level while sleeping?
In 350 healthy people with normal overnight polysomnography, median SpO2 while sleeping averaged 96.5% (SD 1.5). They spent 10% of the night below an average of 94.7% (SD 1.6), and the single lowest reading of the night averaged 90.4% (SD 3.1). People over 60 ran lower: a median of 95.1% and a 10%-of-the-night level of 92.8% (Gries and Brooks, Chest, 1996). These are study averages from one sleep lab, ages 1 month to 85 years. They are not a diagnostic cut-off and not medical advice.
SpO2 while sleeping in healthy people
| Measure | What it means | All healthy subjects (n = 350) | Subjects over 60 |
|---|---|---|---|
| Median SpO2 (Sat 50) | Half the night above this level, half below | 96.5 ± 1.5% | 95.1 ± 2.0% |
| Sat 10 | The level below which the person spent 10% of the night | 94.7 ± 1.6% | 92.8 ± 2.3% |
| Lowest SpO2 (Low Sat) | The single lowest reading, after motion artifact was excluded | 90.4 ± 3.1% | Not given in the abstract |
Source: Gries RE, Brooks LJ. Normal oxyhemoglobin saturation during sleep. Chest 1996;110(6):1489–1492 (abstract). Mean ± SD.
How to read this chart
Gries and Brooks went back through all-night pulse oximetry from a sleep laboratory in a tertiary care hospital. Everyone included had normal results on overnight polysomnography. People with known craniofacial or neurologic abnormalities, or a diagnosed lung disease such as asthma or COPD, were left out. The 350 healthy subjects were 184 male and 166 female, aged 1 month to 85 years. Periods of motion artifact were removed before the numbers were tabulated.
Each column is an average across people. Median SpO2 is the middle of one person's night. Sat 10 is the level that person spent 10% of the night below. The lowest SpO2 is one reading. Because each figure is a mean with a standard deviation, some healthy people sat above it and some below. The study did not publish percentile cut-offs, and none are added here.
None of the measures was related to sex, race, or body mass index. Age was: subjects over 60 had a lower Sat 10 and a lower median. In the same paper, 21 patients with stable asthma did not differ from the healthy group, while 25 patients with obstructive sleep apnea had a significantly lower median, Sat 10, and lowest reading.
The paper is from 1996, and the abstract does not name the oximeter. Its full text, with any finer age breakdown, was not opened for this page, so only the abstract figures appear in the table.
How a sleep study scores oxygen drops
A sleep study does not grade the night against one normal percentage. It scores events. The AASM Manual for the Scoring of Sleep and Associated Events, version 3 (February 2023), is the AASM's reference for scoring polysomnography and home sleep apnea tests. The 2017 AASM diagnostic guideline describes the hypopnea rule from version 2.3: a drop in airflow counts when it comes with a 3% oxygen desaturation or an arousal, with an alternative rule that requires a 4% desaturation. A desaturation in that rule is a drop, not a level. Events per hour of sleep become the AHI. Counting the oxygen drops alone gives the oxygen desaturation index, compared with the AHI in overnight oximetry vs a sleep study.
Awake vs asleep
Daytime resting readings, by age, are on the blood oxygen level chart. The healthy group in Gries and Brooks had a median sleeping level of 96.5%, with a dip toward the low 90s at the lowest point of the night. How a pulse oximeter turns red and infrared light into a percentage is explained in what SpO2 is.
Watch and ring readings at night
A watch or ring that reports overnight SpO2 is making an optical estimate from the wrist or finger, which is not the same set-up as a sleep-lab oximeter. Whether those overnight readings hold up is reviewed in Sensor Bio's is SpO2 accurate at night. A low number on a wearable is a reason to ask a clinician, not a diagnosis.
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Frequently asked questions
What is a normal oxygen level while sleeping?
In Gries and Brooks (Chest, 1996), 350 healthy people with normal sleep studies had a median SpO2 while sleeping that averaged 96.5%. They spent 10% of the night below about 94.7%, and the lowest single reading averaged 90.4%. These are study averages, not a diagnostic cut-off.
Is it normal for oxygen to drop while sleeping?
A small dip is common. In the healthy group studied by Gries and Brooks, the lowest reading of the night averaged 90.4%, about 6 points below the 96.5% median. People with obstructive sleep apnea in the same paper had significantly lower values.
What SpO2 while sleeping is too low?
This page does not set a cut-off, and the source study did not publish one. It reports averages for healthy people. A sleep study scores breathing events and oxygen drops instead of grading the night against one percentage, and a clinician reads overnight oximetry alongside symptoms.
Does sleeping SpO2 fall with age?
Yes, in this study. Subjects over 60 had a median sleeping SpO2 of 95.1% and spent 10% of the night below 92.8%, compared with 96.5% and 94.7% for the whole healthy group.
Is sleeping oxygen different for men and women?
Gries and Brooks found no relationship between any of their sleeping oxygen measures and sex, race, or body mass index. Age was the factor that mattered.
Can my watch tell me my oxygen level while sleeping?
A watch or ring gives an optical estimate of overnight SpO2. It is not a sleep-lab oximeter and is not a diagnosis. Overnight wearable accuracy is a separate question from what a normal sleeping level is.
References
- Gries RE, Brooks LJ. Normal oxyhemoglobin saturation during sleep: how low does it go? Chest 1996;110(6):1489–1492. doi.org/10.1378/chest.110.6.1489
- Kapur VK, Auckley DH, Chowdhuri S, et al. Clinical Practice Guideline for Diagnostic Testing for Adult Obstructive Sleep Apnea: An American Academy of Sleep Medicine Clinical Practice Guideline. J Clin Sleep Med 2017;13(3):479–504. doi.org/10.5664/jcsm.6506
- Troester MM, Quan SF, Berry RB, et al. The AASM Manual for the Scoring of Sleep and Associated Events: Rules, Terminology and Technical Specifications. Version 3. Darien, IL: American Academy of Sleep Medicine; 2023. aasm.org/clinical-resources/scoring-manual/