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What Causes Sleep Apnea?

When you're awake, throat muscles help keep your airway stiff and open so air can flow into your lungs. When you sleep, these muscles relax, which narrows your throat.

Normally, this narrowing doesn’t prevent air from flowing into and out of your lungs. But if you have sleep apnea, your airway can become partially or fully blocked because:

  • Your throat muscles and tongue relax more than normal.
  • Your tongue and tonsils (tissue masses in the back of your mouth) are large compared with the opening into your windpipe.
  • You're overweight. The extra soft fat tissue can thicken the wall of the windpipe. This narrows the inside of the windpipe, which makes it harder to keep open.
  • The shape of your head and neck (bony structure) may cause a smaller airway size in the mouth and throat area.
  • The aging process limits your brain signals' ability to keep your throat muscles stiff during sleep. Thus, your airway is more likely to narrow or collapse.

Not enough air flows into your lungs if your airway is partially or fully blocked during sleep. As a result, loud snoring and a drop in your blood oxygen level can occur.

If the oxygen drops to a dangerous level, it triggers your brain to disturb your sleep. This helps tighten the upper airway muscles and open your windpipe. Normal breathing then starts again, often with a loud snort or choking sound.

Frequent drops in your blood oxygen level and reduced sleep quality can trigger the release of stress hormones. These hormones raise your heart rate and increase your risk for high blood pressure, heart attack, stroke, and arrhythmias (irregular heartbeats). The hormones also can raise your risk for, or worsen, heart failure.

Untreated sleep apnea also can lead to changes in how your body uses energy. These changes increase your risk for obesity and diabetes.

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July 10, 2012 Last Updated Icon

The NHLBI updates Health Topics articles on a biennial cycle based on a thorough review of research findings and new literature. The articles also are updated as needed if important new research is published. The date on each Health Topics article reflects when the content was originally posted or last revised.