How high is too high to sleep?
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Risk starts at about 8,000 feet. A quarter of visitors who sleep above it in Colorado get altitude sickness. Coming from low ground, keep your first night under 9,000 feet, and know that the CDC puts a first night above about 11,150 feet in its high-risk group.
What we’d do
Pick your first bed below 9,000 feet if you’re coming from low ground, even if that means one night in a lower town. If you snore, have sleep apnea, or have had altitude sickness before, talk to your doctor before any trip that sleeps above 8,000 feet.
What are the risk bands?
The CDC says anyone who hasn’t adjusted to altitude is at risk sleeping at 8,000 feet (2,450 m) or higher, and its risk table, for people starting from under 4,000 feet, sorts the first night like this:
| Sleeping elevation, first night | CDC risk | Oxygen in each breath |
|---|---|---|
| Under 9,000 feet (2,750 m) | Low, with a slow climb and no bad history | Over about 72% of sea level |
| 9,000 to 11,150 feet | Medium | About 66% to 72% |
| Over 11,150 feet (3,400 m) | High | Under about 66% |
Past altitude sickness moves you up a band, and so does climbing fast. For a sense of scale, the CDC lists lodging at about 8,150 feet in Vail and 9,600 feet in Breckenridge, Cusco at about 11,000 feet and La Paz at about 12,000.
Think of 8,000 feet as where a pool’s shallow end ends. Most people are fine wading past it, but that’s where you start paying attention to how deep you are.
What happens to sleep up there?
It changes for nearly everyone. Above about 9,000 feet (2,700 m), the CDC says some periodic breathing in sleep, breathing that cycles between deeper breaths and pauses, becomes nearly universal. Your watch may show deeper dips than it does at home. The experts who wrote the 2018 Lake Louise score dropped poor sleep from it, because they decided it’s more likely a direct effect of thin air than a symptom of the illness.
People who already have disordered breathing in sleep are a special case. The CDC recommends a preventive medicine, acetazolamide, for travelers with sleep-disordered breathing heading to high altitude, so it’s a conversation to have with your doctor before you book.
Can your oxygen number tell you when it’s too high?
No. The CDC says people with altitude sickness usually show a number that’s normal for the altitude. The Apple Watch study’s typical ranges stop at about 8,200 feet, where its authors say the straight line breaks. Up there, the morning symptom check and the pacing rules decide (how to prevent it).
Who’s most at risk?
In 3,158 adult visitors to Colorado resorts between 6,300 and 9,700 feet, a quarter got altitude sickness. People who lived below 3,000 feet were 3.5 times as likely to get it, people who’d had it before 2.8 times, and people under 60 twice as likely as older visitors.
5 sources
- CDC Yellow Book, High-Altitude Travel and Altitude Illness, updated April 23, 2025cdc.gov
- Honigman B and others, Acute mountain sickness in a general tourist population at moderate altitudes, Annals of Internal Medicine, 1993europepmc.org
- Roach RC and others, The 2018 Lake Louise Acute Mountain Sickness Score, High Altitude Medicine and Biology, 2018pmc.ncbi.nlm.nih.gov
- NASA Glenn Research Center, Earth atmosphere model, metric unitsgrc.nasa.gov
- Shapiro I and others, Pulse oximetry values from 33,080 participants in the Apple Heart and Movement Study, npj Digital Medicine, 2023pmc.ncbi.nlm.nih.gov
