How sleep apnea affects oxygen saturation while you sleep

Quick takeaways

• When you have obstructive sleep apnea (OSA), breathing pauses can reduce oxygen levels while you sleep.³

• Oxygen levels during sleep normally range between 96% and 100%. In people with OSA, however, these levels can drop below 90%.^1,2

• OSA is associated with serious health problems such as high blood pressure, heart disease, and diabetes. These conditions may be related to repeated drops in oxygen levels during the night.³

• A sleep study can confirm the presence of OSA and show how oxygen levels vary throughout the night.¹⁴

• Continuous positive airway pressure (CPAP) therapy is the most common way to treat OSA. Its goal is to help people with OSA maintain steady breathing during the night.⁴

If you’ve ever woken up tired even after a full night’s sleep, you’re not alone. OSA is a common condition in which breathing is repeatedly reduced or interrupted during sleep, which can cause drops in blood oxygen levels and fragment sleep.³

Learn how OSA can affect oxygen levels during sleep, why this matters for your health, and what you can do to sleep better and take care of your well-being.

What is obstructive sleep apnea (OSA)?

Obstructive sleep apnea (OSA) is a condition in which airflow is repeatedly reduced or interrupted during sleep. During sleep, the relaxation of the muscles that help keep the upper airways open can cause them to narrow or close temporarily, making it difficult for air to pass through.

These pauses can last several seconds and occur many times per hour. When breathing is interrupted, oxygen levels can drop, and the body reacts to resume breathing.³

These pauses also disrupt sleep, even if you don’t fully wake up. Because of this, people with OSA often experience fatigue, sleepiness, or difficulty concentrating during the day.⁵

Each breathing pause is called an apnea. It can last from 10 seconds to more than a minute. During this period, little or no additional oxygen reaches the lungs.⁶

OSA is the most common type of sleep apnea and affects nearly 1 billion people worldwide.⁷

What is oxygen saturation (SpO₂)?

Oxygen saturation (SpO₂) indicates how much of the blood is being oxygenated — in other words, how much of the hemoglobin circulating in the blood is carrying oxygen. It is measured as a percentage (%).²

During healthy sleep, oxygen levels generally range between 96% and 100%. This range is important for the proper functioning of the heart, brain, and other organs during the night. Oxygen saturation can be measured with a small device called a pulse oximeter, placed on the tip of a finger. The device uses light to take the measurement. In people with OSA, oxygen saturation can decrease significantly during sleep.⁹ In some cases, these levels can drop below 90%, a value that health care professionals monitor closely.

Most people don’t usually think about oxygen levels during sleep. However, in those with OSA, these levels can drop dozens or even hundreds of times per night.⁶

How OSA reduces oxygen levels during sleep

In people with OSA, the muscles in the back of the throat relax. As a result, the airways narrow or collapse, blocking the passage of air and preventing more oxygen from reaching the lungs.⁶ During a breathing pause, the body continues to consume oxygen even without additional air coming in. As the pause prolongs, oxygen levels can decrease.^5,6

In OSA, these drops in oxygen levels can repeat many times throughout the night and, in some cases, be quite pronounced. The longer the interruption or reduction in breathing, the greater the drop in blood oxygen can be.⁸ When oxygen levels fall to a certain point, the brain triggers a brief arousal. This arousal allows the airways to reopen and breathing to resume. This usually happens without the person being aware of it.⁶ In people with untreated OSA, this cycle can repeat 5, 15, 30, or even more than 60 times per hour.⁶ Each brief arousal interrupts the normal sleep cycle and can disrupt the deep, restorative sleep that the body needs. Because of this, many people with untreated OSA may sleep eight hours or more and still wake up tired and without the feeling of having rested.

Why drops in oxygen levels during sleep can affect your health

How the body responds to drops in oxygen levels

OSA can cause breathing pauses that reduce the supply of oxygen to organs.⁶

To better understand this, here’s how it happens:

• The heart, lungs, and brain need oxygen to function.¹⁵

• In people with OSA, breathing pauses can reduce the amount of oxygen the body receives during the night.⁵

• When oxygen levels decrease, the body may release stress hormones. This hormonal surge can raise heart rate and cause blood vessels to narrow, which can increase blood pressure.¹⁶

• Over time, this response can contribute to higher blood pressure, including during the day.¹⁰

Health problems associated with low oxygen during sleep

The heart, lungs, and brain need oxygen to function properly. OSA is associated with serious health problems such as:³

• Heart disease
• Diabetes
• Depression
• Stroke
• High blood pressure
• Kidney disease

Sudden drops in oxygen levels during sleep can strain the heart. If you already have heart disease, untreated OSA can worsen the condition.¹¹

The brain needs oxygen continuously, even during sleep. Repeated drops in oxygen levels during the night can affect reasoning, memory, and mood. People with untreated OSA may experience symptoms such as difficulty concentrating and irritability.⁶

Symptoms that may indicate changes in oxygen levels during sleep

Changes in oxygen levels during the night can cause symptoms such as:⁶

• Morning headaches
• Excessive daytime sleepiness, even after a full night’s sleep
• Irritability
• Difficulty concentrating or with memory
• Mood changes

The signs of OSA can easily go unnoticed. You may not be aware of the drop in oxygen levels during sleep. If you experience symptoms during the day, talk to a health care professional. A sleep study can provide information about breathing, heart rate, and oxygen levels during sleep. This information can help you and your health care professional better understand what happens during sleep.

How treatment can help keep oxygen levels more stable

CPAP therapy was developed to help people with OSA maintain steady breathing during the night.⁴ To do this, it uses a device placed next to the bed that delivers a continuous flow of air through a CPAP mask.

When the airways stay open during the night, breathing can occur without interruptions. This can help maintain more stable oxygen levels in the blood, supporting its delivery to the heart, brain, and other organs.²¹

CPAP therapy has efficacy that is widely documented in the scientific literature.¹²

In some people, oxygen levels may remain low during sleep even when OSA is being adequately treated with CPAP. This may indicate the presence of another condition that also affects breathing or gas exchange during sleep. In these cases, the health care professional should investigate the cause and individually evaluate the most appropriate treatment. Depending on the condition identified, it may be necessary to use a device with two pressure levels (bilevel) or, in specific situations, supplemental oxygen.¹⁷

Lifestyle changes can contribute to better treatment outcomes. Among these changes are weight management, the habit of sleeping on your side, and reducing alcohol consumption. These measures can help reduce breathing events during sleep and, consequently, the oxygen drops associated with these events.^18,19

Oxygen levels during sleep can change over time — for example, with changes in weight, with aging, or with the development or progression of other health conditions. For this reason, in some situations, the health care professional may recommend a re-evaluation to check how breathing and oxygenation are during sleep and whether the treatment remains appropriate.²⁰

When to see a health care professional

Talk to a health care professional if you experience:

• Excessive daytime sleepiness
• Morning headaches
• Feelings of irritability or mood changes
• Difficulty concentrating
• Snoring or a feeling of shortness of breath during sleep

It may also be helpful to talk to a health care professional about your sleep if you have heart disease, uncontrolled high blood pressure, or type 2 diabetes. Having a sleep study to investigate OSA can help you better understand what happens during sleep. If you have OSA, treatment can help improve your sleep. In people with OSA and established cardiovascular disease, studies have also found an association between good adherence to CPAP therapy and a lower risk of recurrent cardiovascular events.¹³

Next steps

OSA and oxygen levels are closely related. Breathing pauses can reduce oxygen levels during sleep and affect your health.

If you suspect you have OSA or someone close to you has noticed signs of breathing interruptions during sleep, talk to a health care professional about having a sleep study to investigate OSA. You deserve restorative sleep and oxygen levels that support your health and well-being.

Learn more about your sleep with the Online Sleep Assessment, an initial questionnaire that takes about 5 minutes to complete.

This article is for informational purposes only and does not replace the guidance of health care professionals or proper evaluation, diagnosis, or treatment. If you have questions about any health condition, seek guidance from a qualified health care professional.

References:

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