Before and After CPAP: How Your Body Changes

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CPAP and Weight Loss

Obstructive sleep apnea is closely linked to higher body weight, with each 10% weight gain increasing OSA risk sixfold. Studies also suggest that having OSA may cause a person to gain weight. Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source  

Because of this connection, some researchers have explored whether CPAP therapy might help people lose weight. However, evidence so far is mixed, and CPAP alone does not reliably lead to weight loss.

Will CPAP Help Me Lose Weight?

While older research has suggested CPAP use could help people lose weight, more recent analyses of dozens of studies have found that weight may actually increase Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source after a person with OSA begins CPAP treatment. 

Therefore, people with OSA who are overweight should not rely on CPAP therapy alone to help with weight loss. Instead, experts recommend that people continue other strategies to help reduce body weight.

Does CPAP Cause Weight Gain?

Researchers aren’t entirely sure why treating OSA with a CPAP machine can lead to weight gain. Weight is influenced by a number of factors like diet, exercise, and individual hormone levels, making it difficult to pinpoint whether CPAP therapy is directly linked to weight gain. 

However, researchers have theorized several possible causes of weight gain while people are on CPAP therapy.

• Changes in energy usage: Untreated OSA can cause the body to use more energy during sleep due to low oxygen or heightened nervous system activity. Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source . Studies have also found that basal metabolic rate (calories burned at rest) drops after starting CPAP, resulting in weight gain for some people.
• Having high blood sugar: People with diabetes or impaired blood sugar control are more likely to gain weight after starting CPAP, possibly due to shifts in how their bodies respond to insulin.
• Increases in lean body mass: Other studies suggest weight gain after CPAP use could be due to an increase in lean muscle mass, but not body fat, in some people.

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How Your Body Changes After CPAP

Once you begin CPAP therapy, your body can undergo a range of noticeable changes as your sleep becomes more restorative and your nighttime breathing stabilizes. Some improvements happen quickly, while others build gradually over weeks or months. Together, these changes reflect the body’s recovery from the strain of untreated sleep apnea.

Increased Alertness

Treating OSA with CPAP therapy has been found to reduce daytime sleepiness and increase alertness. Even one night of CPAP use Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source can lead to improved attention the next day.

Some people with OSA might have residual sleepiness, even after treatment with CPAP therapy. People at the highest risk for residual sleepiness include those with more sleepiness to begin with, younger adults, people who use the CPAP machine for less than four hours a night, and those with depression.

Reduced Symptoms of Depression and Anxiety

Studies show that treating OSA with CPAP can reduce symptoms of anxiety and depression Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source , though these effects may be less impactful in people who also have coronary artery disease. 

Although experts aren’t certain about the exact effect OSA has on anxiety and depression, some suggest the low oxygen levels associated with OSA may lead to brain changes that affect mood. This may explain why CPAP therapy improves mental health for some people.

Improved Cardiovascular Health

Research suggests that CPAP therapy may support better cardiovascular health in people with obstructive sleep apnea, although more research is needed. Studies show that CPAP can lower blood pressure—even in people without hypertension—which helps reduce the risk of stroke and heart disease. Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source

Early evidence also indicates that CPAP may decrease nighttime arrhythmias by stabilizing breathing and oxygen levels during sleep. Trusted Source UpToDate More than 2 million healthcare providers around the world choose UpToDate to help make appropriate care decisions and drive better health outcomes. UpToDate delivers evidence-based clinical decision support that is clear, actionable, and rich with real-world insights. View Source Additionally, several small studies have found that CPAP can improve the heart’s ability to pump blood and may help reduce the risk of heart failure or improve heart function in those already diagnosed.

Reduced Heart Failure Risk and Severity

Both OSA and a more rare type of sleep apnea called central sleep apnea often overlap with heart failure Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source . Generally, OSA contributes to the development of heart failure, while central sleep apnea develops after heart failure is present.

Research shows that treating sleep apnea with CPAP can improve the heart dysfunction often seen in heart failure. CPAP appears to support heart health by improving how the left ventricle functions and by calming nervous system activity that influences blood pressure and heart rate.

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Fewer Headaches

OSA can cause a person to wake up with a morning headache, but experts aren’t entirely sure why this is the case. Treating OSA with CPAP has been found to reduce Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source these morning headaches and headaches in general.

Improved Diabetes Symptoms

High blood sugar can cause symptoms like fatigue, blurry vision, frequent urination, increased hunger, and skin infections. While insulin therapy helps manage blood sugar, some people experience insulin resistance, which makes these symptoms harder to control. 

Research suggests that treating OSA with CPAP may help reduce insulin resistance by lowering blood sugar levels and improving insulin sensitivity. Trusted Source European Respiratory Review View Source The idea is that the stress and hormonal changes caused by poor-quality sleep raise blood sugar, and CPAP use helps reverse those effects by restoring more stable, restorative sleep.

Fewer Male Reproductive Issues

While there remain very few studies on this topic, males with OSA may face a greater risk of infertility Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source , as was demonstrated by a large study out of Taiwan.

OSA may play a role in the development of male infertility through many ways, like changes in hormone levels, a build-up of oxygen-containing toxins, insulin resistance, and erectile dysfunction Trusted Source National Center for Biotechnology Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source . More research is needed, but studies are starting to show that CPAP and other OSA treatments may help lower the risk of male infertility.

Healthier Pregnancy

Sleep apnea occurs more commonly Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. View Source during pregnancy, and becomes more severe as the pregnancy goes on. Experts suggest sleep apnea with CPAP therapy can improve fetal health.

Pregnant people who had sleep apnea before pregnancy and are already being treated with CPAP therapy may need to have the pressure settings of their machine adjusted during and after pregnancy, since pregnancy can worsen the severity of OSA.

Potential Side Effects of CPAP Therapy

While CPAP is the most effective treatment for obstructive sleep apnea, some people experience side effects as they adjust to nightly use. Many of these issues improve with proper mask fitting, equipment adjustments, or added comfort features.

• Dry nose, mouth, or throat: Pressurized air can dry out the airway, especially in people who breathe through their mouth at night. Adding heated humidification or using a heated tube often reduces dryness and irritation.
• Nasal congestion or runny nose: The airflow can cause nasal congestion, sneezing, or a runny nose. Humidification, nasal saline sprays, or switching to a full-face mask may help.
• Aerophagia (air swallowing): Some people swallow air during CPAP use, leading to bloating, gas, or stomach discomfort. Adjusting pressure settings, enabling ramp mode, or switching to a different PAP device (such as APAP or BiPAP) may help.
• Skin irritation or allergic reactions: Masks, headgear, or silicone cushions can occasionally cause skin irritation. Hypoallergenic mask liners, gentle cleansers, or alternative cushion materials may resolve the issue.
• Feeling claustrophobic: Wearing a mask can cause anxiety or claustrophobic sensations in some users. Practicing with the mask while awake, choosing a minimalist design, or using a nasal pillow mask can ease the transition.

How to Get Started With CPAP Therapy

After your sleep study confirms a diagnosis of obstructive sleep apnea, your doctor or sleep specialist will write a prescription that includes the machine type, pressure settings, and recommended mask style. From there, you can obtain your equipment through a durable medical equipment (DME) supplier or an online retailer.

Once you receive your CPAP machine, take time to familiarize yourself with the device’s features, such as ramp settings, humidification, and mask fit options. A proper fit is essential for both comfort and effective therapy, so try on different mask styles if needed and adjust the headgear until you achieve a good seal without overtightening. It’s also helpful to practice wearing the mask while awake to ease the transition.

During the first few weeks, consistency is key. Wear your CPAP every night (and during naps) to help your body adjust. If you experience discomfort, dryness, air leaks, or trouble tolerating pressure, reach out to your provider or equipment team for guidance. Small adjustments to pressure settings, humidity, or mask type can make a significant difference. With regular use and proper support, most people find CPAP becomes an easy and effective part of their nightly routine.

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