How sleep apnea affects the body, system by system

Sleep apnea affects far more than sleep. Each pause in breathing can lower oxygen levels and jolt the body awake, and when that happens many times a night, the strain reaches the heart, blood vessels, brain, metabolism and more. This guide walks through each body system, what the research links to sleep apnea, and where to read more. The encouraging part is that sleep apnea is treatable, and treatment helps several of these effects.

How does sleep apnea affect the body?

Obstructive sleep apnea affects the body through three repeated stresses: falling oxygen levels, surges in the nervous system, and broken sleep. An American Heart Association scientific statement describes these as intermittent drops in blood oxygen, swings in the nervous system's control of the body, and sleep fragmentation, all caused by the airway closing again and again.

NHLBI explains it in plain terms. Sleep apnea can cause low oxygen during sleep and stop you getting enough good-quality sleep. It also takes a lot of effort to restart breathing many times a night, and NHLBI says this can damage organs and blood vessels.

Here's an overview of the main systems, with links to our deeper guides.

How does sleep apnea affect the brain and mood?

Sleep apnea affects the brain mainly by robbing it of rest. NHLBI says untreated sleep apnea can cause problems with concentrating, remembering things, making decisions and controlling behavior. The NHS lists trouble concentrating, mood swings and headaches on waking among the daytime symptoms.

Longer-term links are being studied closely. A 2020 review in Sleep Medicine Reviews, covering three decades of research, found that in middle-aged adults sleep apnea is often tied to mild problems with attention, memory and executive function. In older adults it was associated with developing mild cognitive impairment or Alzheimer's disease. The review also found that CPAP may help cognition in people with sleep apnea who have Alzheimer's. NHLBI lists dementia in older adults among the conditions sleep apnea may raise the risk of.

Mood is affected too. A 2026 meta-analysis of 23 studies found high rates of overlap between sleep apnea and mood disorders, including major depression and bipolar disorder. That doesn't prove one causes the other, but it's a good reason to mention sleep symptoms if you're being treated for low mood. If you often wake with a headache, our guide to morning headaches covers the common causes.

How does sleep apnea affect the heart?

Sleep apnea is closely tied to heart disease. The AHA statement reports sleep apnea in 40 to 80% of people with high blood pressure, heart failure, coronary artery disease, pulmonary hypertension, atrial fibrillation and stroke. It also says sleep apnea is often missed and undertreated in heart care, despite how common it is in heart patients.

NHLBI lists atrial fibrillation, atherosclerosis, heart attack, heart failure, pulmonary hypertension and stroke among the heart and blood vessel conditions sleep apnea may raise the risk of. The AHA recommends screening for sleep apnea in people with recurrent atrial fibrillation after treatment and in people with pulmonary hypertension. Our guide to whether sleep apnea is deadly looks at what this means for long-term health.

How does sleep apnea affect blood pressure?

Sleep apnea can push blood pressure up and make it harder to control. NHLBI lists difficult-to-control high blood pressure among the conditions linked to sleep apnea. The AHA recommends screening for sleep apnea in people whose high blood pressure is resistant to treatment or poorly controlled.

Treatment helps here. The NHS says CPAP can reduce the risk of problems linked to sleep apnea, such as high blood pressure. Our article on sleep apnea and high blood pressure explains how the breathing pauses raise blood pressure and how much CPAP lowers it.

How does sleep apnea affect metabolism and weight?

Sleep apnea is linked to type 2 diabetes and metabolic syndrome, a cluster of risk factors that includes high blood sugar and blood pressure. NHLBI lists both among the conditions sleep apnea may raise the risk of.

Weight plays a part in both directions. The NHS lists losing weight among the lifestyle changes that can sometimes treat sleep apnea, and suggests it for people who are overweight. Our guide to sleep apnea and weight gain explains the two-way link in more detail.

Does sleep apnea affect the liver?

Sleep apnea is linked to non-alcoholic fatty liver disease, especially in people with obesity. A 2023 systematic review in the International Journal of Obesity included 28 studies and found significant links between sleep apnea and fatty liver disease in most of them. It points to repeated drops in oxygen as part of the reason.

The research is still messy. The review found that the apnea-hypopnea index on its own was a poor predictor of fatty liver, and the studies used 14 different liver tests, so the authors couldn't combine them in a meta-analysis. They called for better-designed studies. For now, it's fair to say the two often go together, but how much sleep apnea itself drives liver disease isn't settled.

How does sleep apnea affect the eyes?

Sleep apnea is linked to several eye conditions. NHLBI lists glaucoma, dry eye and keratoconus, a thinning and bulging of the cornea, among eye problems sleep apnea may raise the risk of.

Glaucoma has the most research behind it. A 2023 meta-analysis in Eye pooled 46 studies with more than 4.5 million people. After adjusting for age, sex and conditions such as high blood pressure, diabetes and heart disease, people with sleep apnea had up to 40% higher odds of glaucoma. The authors called for studies on whether treating sleep apnea slows glaucoma. If you have either condition, it's worth telling both your eye doctor and your sleep doctor.

How does sleep apnea affect sexual health?

Sleep apnea is strongly associated with sexual problems. NHLBI lists sexual dysfunction and decreased libido among the symptoms of sleep apnea that you may notice yourself.

For men, the link with erectile dysfunction is well documented. A 2026 meta-analysis in the International Journal of Impotence Research found erectile dysfunction in 59 to 69% of men with sleep apnea across the studies it reviewed. More severe sleep apnea and lower oxygen levels during sleep were tied to worse erectile function. The authors noted that age was an important confounder, and that CPAP was associated with improvements in erectile function in the studies they included, though the size of the improvement varied.

How does sleep apnea affect daytime life?

Sleep apnea affects daytime life mainly through tiredness. NHLBI says daytime sleepiness can lead to problems with learning, focusing and reacting. It also lists dry mouth, headaches, insomnia and waking often to urinate among the symptoms. The NHS adds feeling very tired, finding it hard to concentrate and mood swings. Our guide to waking up tired covers other reasons for unrefreshing sleep.

Sleepiness is a safety issue on the road. A 2009 meta-analysis in the Journal of Clinical Sleep Medicine concluded that people with sleep apnea are clearly at higher risk of a car crash. It estimated the crash rate was likely between 1.21 and 4.89 times that of comparable people without sleep apnea, and called untreated sleep apnea a significant contributor to crashes.

What other parts of the body can it affect?

NHLBI lists several more conditions sleep apnea may raise the risk of: gastroesophageal reflux disease, chronic kidney disease, pregnancy complications, worse asthma attacks and some cancers, including pancreatic, kidney and skin cancer. Some of these links are newer and less studied than the heart and blood pressure findings. Our guide to sleep apnea in women covers pregnancy and other signs that are easy to miss.

Does treatment reverse the effects?

Treatment helps with several effects, and that's the most hopeful part of this picture. The NHS says CPAP can improve breathing during sleep, improve sleep quality, reduce tiredness and reduce the risk of problems linked to sleep apnea, such as high blood pressure. It notes that CPAP works best when used every night. Other options include mouthpieces that hold the airway open, surgery, mouth and face exercises, and nerve stimulation devices.

Not every link has been tested in treatment trials. For some effects, such as glaucoma and fatty liver, researchers are still asking whether treating sleep apnea changes the outcome. Our guide to sleep apnea treatment options explains the choices, and getting used to CPAP helps if the mask is the sticking point.

If you snore loudly, stop breathing or gasp at night, or feel tired all the time, see a doctor. The NHS says sleep apnea can be serious if it's not diagnosed and treated. This article is general information, not medical advice.

Read next

• 10 warning signs of sleep apnea you shouldn't ignore
• Sleep apnea treatments explained
• Is sleep apnea deadly? What the research says

* This content is for informational and educational purposes only and is not medical advice. It is not intended to diagnose, treat, cure or prevent any disease or health condition. Talk to a qualified healthcare provider about your health.