The potential complications of untreated sleep apnea

Obstructive sleep apnea (OSA) is not just an isolated sleep disorder. When left untreated, it comes with a range of complications that are well documented by medical research, particularly on the cardiovascular and metabolic level.

To understand these complications, it helps to look at what happens during a night of apneas. Each episode strings together three assaults on the body. First, a drop in blood oxygen, followed by a sharp reoxygenation when breathing resumes — known as intermittent hypoxia. Next, strong pressure swings in the chest, as the person tries to inhale against a closed pharynx. Finally, a micro-arousal that sharply activates the sympathetic nervous system, the “stress” system. Repeated dozens of times per hour, hundreds of times per night, for years, this cycle promotes inflammation, oxidative stress, and dysfunction of the vessel walls. These are the mechanisms common to most of the complications described below.

High blood pressure, the most common complication

The prevalence of high blood pressure among people with OSA is considerable: it is estimated at between 35% and 80% depending on the study. Conversely, among people whose hypertension remains resistant despite three treatments, a large majority have sleep apnea. This is why international cardiology guidelines recommend screening for OSA in any case of resistant hypertension.

This link is mainly explained by intermittent hypoxia and repeated micro-arousals, which activate the sympathetic system. This activation partly persists during the day, well after the night has ended. Normally, blood pressure drops by 10% to 20% during sleep. In people with apnea, this nighttime drop is often absent, and high blood pressure at night is associated with a higher cardiovascular risk.

Treating OSA with continuous positive airway pressure (CPAP) has a beneficial effect on this high blood pressure, provided the device is worn at least 4 hours per night. The average effect remains modest, on the order of a few millimeters of mercury, but it is more pronounced in people with resistant hypertension and good adherence. CPAP therefore doesn't replace blood pressure medication — it complements it.

A sharply increased cardiovascular risk

Large observational studies point in the same direction. A frequently cited Spanish cohort followed more than 1,600 men for about ten years (Marin et al., The Lancet, 2005). Patients with untreated severe OSA had a risk of fatal cardiovascular events (heart attack, stroke) roughly 2.9 times higher. Their risk of non-fatal events (heart attack, stroke, bypass surgery, angioplasty) was roughly 3.2 times higher, compared with people without apnea. This excess risk persisted after adjusting for age, smoking, blood pressure, and cholesterol: OSA therefore appears to be a risk factor in its own right.

Beyond heart attack and stroke, OSA is associated with other heart conditions. Atrial fibrillation, a common heart rhythm disorder, is more common and recurs more often after treatment in people with untreated apnea. Heart failure is another, as are nighttime conduction disorders. The American Heart Association published a dedicated scientific statement in 2021 on the links between sleep apnea and cardiovascular disease.

An important scientific nuance is needed here, though. These studies show an association, and demonstrating that treating OSA reduces these events has proven harder than expected. The large randomized SAVE trial (McEvoy et al., New England Journal of Medicine, 2016) followed more than 2,700 patients who already had cardiovascular disease for nearly 4 years. It did not show a reduction in new cardiovascular events with CPAP. Several explanations have been proposed. Patients used their device only about 3 hours a night on average. Highly sleepy participants, perhaps those at highest risk, had been excluded. And finally, cardiovascular disease was already established. In that same trial, however, CPAP clearly reduced sleepiness and improved quality of life and mood.

The current conclusion is therefore nuanced. OSA is a serious cardiovascular risk marker that warrants screening and management. The cardiovascular benefit of treatment is probably linked to sufficient device use, and it remains an active area of research.

A metabolic impact as well

OSA is also associated with type 2 diabetes, and the relationship appears to run both ways, with each condition able to worsen the other. Intermittent hypoxia and sleep fragmentation increase insulin resistance and the secretion of stress hormones like cortisol. In people who already have diabetes, untreated OSA is associated with poorer blood sugar control. OSA is also linked to cholesterol and triglyceride abnormalities (dyslipidemia) and to fatty liver disease — the buildup of fat in the liver. Nighttime hypoxia may promote the progression of this fatty liver toward inflammation and fibrosis.

These associations are reinforced by shared underlying factors: abdominal obesity promotes OSA, diabetes, and fatty liver disease all at once. A lack of restorative sleep also disrupts appetite hormones, which can sustain weight gain. This is why the Société Francophone du Diabète and other professional societies recommend screening for OSA in patients with an at-risk cardio-metabolic profile. If this applies to you, the hub's Am I at risk of diabetes? and Do I have fatty liver disease? tools usefully complete this picture.

Daytime sleepiness and everyday safety

Beyond internal complications, the excessive daytime sleepiness caused by untreated OSA has concrete consequences. It is a recognized cause of road accidents and workplace accidents, particularly in jobs that demand sustained alertness: professional driving, working at height, operating machinery. Several studies have shown a higher risk of road accidents among drivers with untreated apnea. This risk drops markedly once treatment is properly followed.

Regulations account for this risk. Since a 2014 European directive, moderate-to-severe OSA combined with excessive sleepiness is among the conditions that can be incompatible with driving. In France, a March 28, 2022 order governs this question. Resuming driving is possible after an assessment showing the treatment is effective. Professional drivers (trucks, public transport) undergo a medical check, while for a standard driver's license, it's the driver's own responsibility. In practice, once treatment is in place and effective, the vast majority of people drive normally.

A mental health impact too

Less often discussed than the cardiovascular complications, untreated OSA is also associated with an increased risk of mood disorders, particularly depressive symptoms and irritability. Chronic sleep fragmentation partly explains this link, but intermittent hypoxia may also directly affect certain brain functions. Memory, attention, and executive function (planning, organizing) problems are also described. Research is exploring a possible link with long-term cognitive decline.

This dimension is sometimes overlooked when screening for OSA. Fatigue, loss of drive, difficulty concentrating, and irritability can suggest depression, and the two conditions often coexist, which is why it's worth exploring both possibilities. Several studies have observed an improvement in depressive symptoms after starting well-followed CPAP treatment. If you recognize these symptoms in yourself, the Am I depressed? test can help you take stock before talking to your doctor.

Some good news nonetheless

These risks are not inevitable: they are precisely why early screening makes sense. Once a diagnosis is made and appropriate treatment is put in place, several of these complications can be better controlled, high blood pressure in particular. Benefits generally appear within a few weeks to a few months of well-followed treatment. Effects on sleepiness, driving alertness, and quality of life are often the fastest and clearest, sometimes as early as the first few nights.

Weight loss, cutting back on alcohol, and physical activity also act on both OSA and the cardio-metabolic risk factors that come with it. Identifying OSA is thus often an opportunity for a broader review of your cardiovascular health, which can be the real benefit of the process. A tool like the STOP-BANG score can be a first step toward this screening.