Myth or fact

One low night means you have sleep apnea

Short answerNo

By GyroscopeUpdated November 14, 202611 sources

No. In 350 people whose sleep studies came back normal, the lowest point of the night averaged about 90, and plenty went lower. One evening of drinks can keep oxygen dips raised the next night too. A pattern over several nights, or someone seeing you stop breathing, is what points to sleep apnea, and only a sleep study can tell you.

Why it sounds right

Sleep apnea is the night condition everyone has heard of, and it’s about oxygen dropping in sleep. When your watch shows an 86 at 3:12 am, the dots connect themselves. The number is right there on your wrist, it’s lower than the chart, and it happened while you slept. What that leaves out is how low a normal night goes.

Does one rainy day make a wet climate?

One wet Tuesday tells you it rained on Tuesday. You need a season of weather to know the climate. Nobody moves house over one storm.

Sleep apnea is the climate, a pattern of breathing stopping and starting many times a night, night after night, and one low night is a single wet Tuesday.

How low does a normal night go?

In 1996 two researchers, Gries and Brooks, went back through 350 overnight sleep studies that came back normal. The lowest oxygen of the night averaged 90.4, with most people between about 84 and 97. People over 60 ran a little lower. People with obstructive sleep apnea in the same study ran lower.

Your watch agrees. Apple says “slightly lower values while sleeping are expected” and some people see values under 95. In 33,080 Apple Watch wearers, blood oxygen was lowest around 1 am.

If your skin is darker, a sensor can show higher than your true oxygen, so a normal-looking night is less reassuring and a pattern of low ones means more. In hospital patients whose finger oximeter showed 92 to 96, true oxygen was under 88 for 11.7% of Black patients’ measurements and 3.6% of White patients’.

What makes one night low?

• Drinks. In 1981, 20 men with no sleep complaints were given a measured dose of alcohol. Their oxygen dips went from 118 to 226 in a night, and stayed raised the next night with no alcohol at all. Across 14 trials, alcohol lowered the night’s lowest point by 1.25 points.
• Elevation. A night in the mountains runs lower. The watch study’s night average fell about 1.2 points per kilometre (3,300 feet).
• Sleeping on your back, for people whose airway narrows in sleep.
• The device. A loose band, cold wrists, a tattoo under the sensor and moving all change the number, Apple says.

What does point to sleep apnea?

Repetition, and the signs doctors ask about. Loud snoring, feeling tired in the day, someone seeing you stop breathing, high blood pressure, a BMI over 35, age over 50, a large neck and being male are the eight items on the STOP-Bang checklist. In studies of it, people with more of those signs were far likelier to have moderate to severe apnea on a sleep study, from about 18% with two or fewer to 60% with seven or eight. NHLBI adds gasping for air.

Even then, a watch or a checklist can only point. The 2017 US sleep medicine guideline says questionnaires and clinical tools shouldn’t be used on their own to diagnose sleep apnea, and calls for a lab study or a home sleep apnea test. When does a low night mean a sleep study? covers both.

HRV has its own version of this myth, the single low morning. hrv.guide’s answer makes the same case for the heart.

The best case for the myth

“If my oxygen dropped to 85, something happened, and I’d rather catch it early.” Something did happen, and it may have a name you already know, such as last night’s wine or the hotel at 9,000 feet. Catching it early is the reason for the three-night check, which costs nothing and gives your doctor a pattern instead of one number. If someone has seen you stop breathing, skip the waiting and ask about a study now.

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