Sleep apnea: weight is the main risk factor — and only a sleep study confirms it

Loud snoring, breathing pauses noticed by whoever sleeps next to you, choking in the middle of the night. In the morning, the feeling of not having rested; in the afternoon, the struggle not to doze off at the computer or in traffic. That is the typical picture of obstructive sleep apnea (OSA) — one of the most common diseases in clinical practice and one of the least diagnosed.

This article follows the UpToDate review on the clinical presentation and diagnosis of OSA in adults, updated in May 2026, and the studies it cites. It focuses on two questions: which risk factor weighs the most — literally — and what actually confirms the diagnosis.

What obstructive sleep apnea is

During sleep, the muscles that keep the throat open relax. In people with OSA, the upper airway collapses, completely or partially, several times an hour. Airflow stops (apnea) or drops (hypopnea), oxygen falls, and the brain wakes for a few seconds to reopen the passage. The person almost never remembers these arousals — but sleep becomes fragmented, and the body spends the night in cycles of breathlessness and stress.

Severity is measured by the apnea-hypopnea index (AHI), the number of events per hour of sleep: 5 to 14 is mild, 15 to 30 is moderate, above 30 is severe.

How common it is

Far more than people imagine. In the São Paulo Epidemiologic Sleep Study, which performed polysomnography on 1,042 randomly selected adults from the city's population, 32.8% had OSA — one in three. Worldwide, an estimated 936 million people aged 30 to 69 have the disease, 425 million of them in its moderate to severe form.

And prevalence is rising. In the United States, between 1990 and 2010, it went from 11% to 14% in adult men and from 4% to 5% in women — an increase that tracks the growth of obesity.

Obesity: the risk factor that weighs the most

OSA has several risk factors: age, male sex, differences in the shape of the face and airway, smoking, family history, nasal congestion. None weighs as much as obesity.

The Brazilian numbers are the most telling. In the São Paulo study, after adjusting for age, sex and socioeconomic status, people with obesity had 10.5 times higher odds of OSA than people of normal weight. Moderate to severe apnea was present in 11% of normal-weight men, 21% of overweight men and 63% of men with obesity.

The relationship is not merely statistical: it moves with the scale. In the Wisconsin cohort, which repeated polysomnography in 690 adults four years apart:

• gaining 10% of body weight raised the AHI by about 32% and multiplied by six the odds of developing moderate to severe apnea;
• losing 10% of body weight lowered the AHI by about 26%.

The mechanism is largely mechanical. Fat accumulates in the neck, the tongue and around the pharynx and narrows the airway; abdominal fat reduces lung volume and the traction that helps keep the airway open. That is why neck and waist circumference are associated with OSA even more than body mass index: the risk is particularly high in men with a neck larger than about 43 cm (17 inches) and in women larger than about 41 cm (16 inches).

The connection goes further. OSA is independently associated with insulin resistance, type 2 diabetes and metabolic dysfunction-associated steatotic liver disease — the same conditions that accompany obesity. In one study, people with severe OSA had about a 30% higher risk of developing diabetes; fatty liver disease is two to three times more frequent. If you have read this site's article on obesity as a chronic inflammatory disease, sleep apnea is a piece of that same picture.

An honest caveat: being thin is not absolute protection. Jaw differences, large tonsils and other anatomical features cause OSA in people of normal weight — and a subtler form, with arousals but no complete pauses, is common in thin women.

Signs worth attention

Most people with OSA have daytime sleepiness, or snoring with pauses and choking noticed by a bed partner. It is worth asking about:

• Daytime sleepiness: dozing while reading, watching television, in meetings — or driving. Often described only as "tiredness" or "low energy".
• Loud, habitual snoring, with pauses, choking or snorting. Choking at night is the most useful sign for suspecting OSA.
• Morning headaches, present in 10% to 30% of untreated patients.
• Repeated awakenings and insomnia: about a third of people with OSA complain of insomnia rather than sleepiness — especially women.
• Getting up to urinate during the night.
• Hard-to-control high blood pressure, atrial fibrillation, heart failure.

Snoring alone says little: it is far more common than apnea, and most people who snore do not have OSA. On the other hand, mild snoring together with a BMI below 26 makes moderate or severe disease unlikely.

How the diagnosis is made

This is the most important point of the article: OSA is not a clinical diagnosis. History and physical examination define who should be investigated, but only a sleep study confirms — or rules out — the disease.

There are two options:

• In-laboratory polysomnography — the gold standard. It is the choice when other sleep disorders are suspected (narcolepsy, periodic limb movements), when there are conditions that alter breathing during sleep (COPD, advanced heart failure, chronic opioid use, stroke), when mild disease is suspected, or in jobs where dozing off endangers the person and others — drivers, pilots, machine operators.
• Home sleep apnea testing — an appropriate alternative for people with a high probability of moderate to severe OSA without those complications: daytime sleepiness plus loud snoring, witnessed pauses or choking. If the result is negative or inconclusive and suspicion remains, the next step is polysomnography, not a repeat home test.

The diagnosis is confirmed by 5 or more events per hour with symptoms, or by 15 or more events per hour even without symptoms.

What about questionnaires such as STOP-Bang? They help select whom to investigate — they catch most cases, but they also flag many people who do not have the disease. They do not replace the sleep study. Nor is it recommended to apply them broadly to people without symptoms: the US Preventive Services Task Force (USPSTF) concluded that the evidence is insufficient for that kind of screening.

Why treatment matters

Untreated OSA is not just a sleep problem. Car crashes are two to three times more frequent. Attention, memory and mood worsen. Moderate to severe disease raises the risk of hypertension, coronary disease, arrhythmias, heart failure and stroke, and severe disease is associated with higher mortality.

Weight at the center of treatment

Treatment depends on severity and symptoms. CPAP — a device that keeps the airway open with positive pressure during sleep — remains the foundation for symptomatic moderate to severe disease. But in a person with obesity, treating weight is not an extra: it is treating the cause.

Recent data confirm what the Wisconsin cohort suggested. In the SURMOUNT-OSA trial, published in the NEJM in 2024, tirzepatide lowered the AHI by about 25 to 29 events per hour over 52 weeks, versus 5 to 6 with placebo, in adults with obesity and moderate to severe OSA. In October 2025, Anvisa approved tirzepatide for this use in Brazil. Retatrutide, not yet approved, lowered the AHI by 32 to 34 events per hour over 80 weeks in the TRIUMPH-1 trial.

Medication does not replace assessment. The decision to use CPAP, medication, both or other strategies — oral appliances, surgery in selected cases — is individual. And some measures apply to everyone: avoiding alcohol and sedatives at night, which can worsen apneas, and treating a blocked nose when it gets in the way of breathing.

For the patient

If you snore loudly, wake up tired, or someone has noticed that you stop breathing in your sleep, that deserves investigation — especially if there is excess weight, high blood pressure or diabetes. The question is not "do I snore?". It is: is my sleep costing me something during the day?

Sleep apnea has an objective diagnosis, effective treatment and a direct relationship with weight. Investigating is the first step — and, for many people, treating apnea and treating obesity turn out to be the same care.