For decades, sleep disturbance was a punch line: the cartoon dad snoring, the disgruntled partner burying their head under a pillow. But science is beginning to paint a less jovial picture. Sleep apnea—a relatively common disorder where breathing repeatedly stops and starts during sleep—is now being taken seriously as a potential biomarker for a host of major health conditions, from cardiovascular disease to Alzheimer’s, even anxiety and depression.
“Sleep is just as important for health as diet and exercise,” says Marishka Brown, director of the US National Center on Sleep Disorders Research. “Poor sleep affects both your mental and physical health; it contributes to cardiovascular disease, increases all-cause mortality, and raises risk factors like obesity, hypertension, and diabetes. And these impacts are independent—they’re not just knock-on effects from something else. Sleep is foundational.”
Obstructive Sleep Apnea (OSA) is one of the most common types of apnea, affecting an estimated 1 billion people worldwide. It occurs when the upper airway repeatedly collapses during sleep, interfering with breathing and lowering oxygen levels. The brain responds by jolting the sleeper awake—sometimes hundreds of times a night—before letting them drift off again, often unaware.
Sufferers may feel exhausted during the day and can experience memory problems. But more than this, the latest research suggests that sleep apnea may play an early and direct role in serious long-term illnesses, especially those affecting the brain.
“Traditionally, sleep apnea was thought of as a disorder that increases with age—especially in men—and leads to heart problems, maybe stroke,” says Bryce Mander, associate professor of psychiatry and human behavior at UC Irvine. “But over the last decade, it’s become clearer that it’s also a risk factor for neurological illnesses like Alzheimer’s and other neurodegenerative diseases.”
Each pause of breath triggered by apnea causes a drop in oxygen levels and a surge in adrenaline for the sleeper. “Over time, that raises the risk of high blood pressure, heart disease, and stroke,” says Atul Malhotra, a sleep medicine specialist and professor at UC San Diego. “There’s strong evidence now that sleep apnea is not just a marker of being unfit. Lean people get sleep apnea too,” he adds.
Hypoxemia—when oxygen levels in the blood are lower than normal—increases inflammation and oxidative stress on cells, explains Mander. “It’s associated with vascular pathology in the brain. So, your blood vessels become damaged, and that can damage the surrounding brain tissue,” he says.
This damage can accelerate the trajectory of a disease like Alzheimer’s or make the brain more vulnerable to it—and researchers now know the effects may appear years before outward symptoms.
A 2015 New York University study found that people with sleep-disordered breathing developed mild cognitive impairment, including Alzheimer’s, up to 10 years earlier than those without. However, those who received treatment for their sleep apnea had the same onset age as those without sleep-disordered breathing.
“Duration of untreated illness is one of the biggest predictors of long-term damage,” says Mander. “The longer you have OSA, the more havoc it can wreak on the body and the brain.”