Causes and Risk Factors of Obstructive Sleep Apnea

Obstructive sleep apnea (OSA) is a condition that negatively affects sleep and health, caused by physical disruption of normal breathing. It may be associated with snoring and other symptoms. The upper airway can be obstructed during sleep due to a number of causes, many of them interrelated. The responsible locations in the nose, mouth, or throat where breathing becomes restricted can vary widely from one case of obstructive sleep apnea to another.

Important causes of and risk factors for obstructive sleep apnea include anatomy, such as structures that would narrow the airway like a deviated septum or potential enlargement of the tongue and tonsils, as well as genetic factors or syndromes which further affect airway shape.

Other factors include hormonal changes, obesity, and behaviors like sleeping on the back, drinking alcohol late, or smoking, all of which make normal breathing during sleep more difficult. Let’s further explore these causes.

Common Causes

The main mechanism of OSA is the periodic collapse of the soft palate and base of the tongue into the upper airway during sleep.

Anatomical Traits

Anatomical traits of the nose, mouth, or throat may affect the normal flow of air. Contributors may include abnormalities such as:

• Narrowing of the nose
• Nasal valve collapse
• Nasal septum deviation
• Turbinate hypertrophy
• Elongated soft palate
• Enlarged uvula
• Tonsil enlargement
• Narrowing of the throat (posterior oropharynx)
• High arched palate
• Deficiency of the upper jaw or midface (maxilla)
• Loss of teeth (edentulousness)
• Increased tongue size (macroglossia)
• Recessed lower jaw (micrognathia or retrognathia of the mandible)

Other anatomical differences that constrict airflow and may cause chronic OSA are heritable characteristics driven by genetics or developmental differences. These are explored in more detail in the “Genetics” section below.

Temporary Causes

Some temporary cases of OSA may be caused by infection or inflammation of the soft tissues lining the airway, including colds, allergies, adenoiditis, tonsillitis, and tongue swelling.

Allergic rhinitis, a condition characterized by nasal congestion that is often related to household or environmental allergens, may increase the risk of experiencing OSA. Congestion due to allergies or colds may lead to mouth breathing. In sleep this may allow the lower jaw to shift back and the tongue to partially or fully occlude the airway.

Obesity

The most common modifiable risk factor for obstructive sleep apnea may be obesity. Fat deposits (also known as adipose tissue) at the base on the tongue and along the pharynx as well as reduced lung capacity can increase the frequency of airway collapse during sleep.

In addition to physical restriction, adipose tissue is linked to hormonal changes and upregulation of immune signaling. Sleep apnea events may further provoke release of cortisol hormone as the brain attempts to rouse the individual during recurrent episodes of oxygen desaturation and elevation of carbon dioxide levels.

Metabolic Disorders

It is possible that metabolic disorders may also exacerbate breathing difficulties. For example, about 70% of people with diabetes experience OSA to some extent, and the cortisol released by the disorder may worsen their blood glucose control.

Sex Hormones

Men have a higher risk of developing sleep apnea, possibly related to the effects of testosterone, and women seem to be protected by the effects of progesterone and estrogen early in life.

The risks for sleep apnea in women increase at menopause, with the removal of ovaries, and in polycystic ovarian syndrome.

Sleep Position

Sleep position can negatively affect the ability to keep the airway open during sleep. In particular, the supine position (sleeping on one’s back) has the greatest effect, especially in the context of mouth breathing.

The tongue can flop backwards and shift into the throat, making it more difficult to maintain an open passageway to allow the normal flow of oxygen into and carbon dioxide out of the lungs. Ideally, the neck would be in a neutral to extended position to optimize airflow through the throat.

REM Sleep

OSA is often worse during REM sleep. This is the portion of sleep where you dream and also the most restful period of sleep which allows you to feel refreshed and well rested the next day. REM sleep occurs roughly every 90 minutes to two hours through the night, with most of it is present towards morning in the last one-third of typical sleep.

REM includes the relaxation of skeletal muscles to prevent the acting out of dreams. Loss of muscle tone also affects the airway musculature, leading to further collapse.

This may contribute to longer sleep apnea events and more significant oxygen desaturation, especially in the context of obesity that may exacerbate hypoventilation. It is also a common cause of middle-of-the-night and early morning awakenings that contribute to insomnia.

Surgery

Surgery may exacerbate or contribute to sleep apnea in susceptible individuals. Anesthesia may include sedatives, muscle relaxants or paralytics, and narcotic pain medications, all of which increase the risks of sleep apnea occurring

Furthermore, after intubation in a surgical setting, manipulation of the tissue of the throat can lead to swelling (upper airway edema) and complications. Excessive mucus production and decreased conscious clearance may cause a buildup that decreases airway diameter and causes breathing troubles. This restriction of breathing can cause or exacerbate OSA.

Age

Sleep apnea may be a nearly lifelong disorder due to a genetic predisposition, and occurs in some children throughout childhood and into adulthood.

Premature birth is a major risk factor to develop OSA at a younger age. Children born before 27 weeks of gestation experience sleep apnea at nearly four times the rate of children born at term. However, relative birth weight does not appear to be causal in this case. Only gestational age—and therefore the level of facial and respiratory development—appears to affect risk of sleep apnea in infancy.

Middle-aged people begin to experience OSA more often, with men getting an earlier start compared to women. The effect of aging may be because of the increased number of risk factors, such as weight gain, and other variables that also contribute to cardiovascular disease.

Elderly people may experience OSA at still higher rates due to a decline in the function of areas of the brain dedicated to neuromuscular action, loss of muscle tone along the airway, and higher rates of denture use (and removal during sleep affecting jaw and tongue positioning). As people get older the sex difference in sleep apnea prevalence is reduced.

Genetics

Risk factors for OSA may be genetically linked, sometimes associated with specific syndromes and often making the condition likely to run in families. First-degree relatives of an individual with OSA are more likely to snore or have observed apneas, after controlling for obesity, age, and gender.

Around 40% of the variance in apnea-hypopnea index (AHI) has been shown to be explained by genetic factors. Of the causes and risk factors listed above, many relate to anatomy and have some genetic element. There may be a correlation, but the underlying mechanisms that contribute to the disorder may as yet be unknown.

Genes

Genomic research continues to be done and candidate genes that increase the risk of developing OSA have been identified, but more work is needed to understand this relationship.

Some genes identified or suspected as risk factors that may contribute to sleep apnea include:

• TNF-α: used to signal cell death of inflamed cells and immune response
• PTGER3: makes a receptor to a prostaglandin lipid with endocrine-like functions
• LPAR1: makes a receptor for lysophosphatidic acid, important for lipid signalling
• ANGPT2: modulates vascular and inflammatory responses, affects oxygen saturation
• GPR83: expressed in parts of the brain dedicated to control of parasympathetic and autonomic functions, including non-conscious breathing and laryngeal reflexes
• ARRB1: important for development of blood vessels, can increase risk of hypoxia
• HIF‐1α: regulates a factor important for controlling sensitivity to hypoxia in the carotid artery

Genetic Disorders

Other cases of OSA are caused directly by the anatomical and physiological effects of identifiable congenital disorders. While some disorders and syndromes have a characteristic set of anatomical alterations, some have more subtle differences that may be present in a family and ultimately cause OSA.

These may include differences in craniofacial morphology and how the body responds to protect breathing during sleep. 

Some of the genetic syndromes that are associated with sleep apnea include: 

• Down syndrome (trisomy 21) is a genetic disorder which negatively affects sleep. The majority of children with Down syndrome experience a form of sleep apnea from an early age. Several traits including an altered midface, impacting the structure of the nose and throat, as well as enlargement of the tongue and tonsils. This may increase vulnerability to infection and lead to problems with obstructed breathing during sleep. OSA tends to worsen with age.
• Pierre-Robin syndrome produces a characteristic underdeveloped lower jaw (mandibular hypoplasia), cleft palate, and backwardly displaced tongue (glossoptosis). Affected newborns who require respiratory support after birth are more likely to experience OSA.
• Ehlers-Danlos syndrome is a genetic disorder that causes problems in the connective tissue of the body. The structure of the face can be altered in a way that increases the frequency of airway collapse. People with Ehlers-Danlos syndrome experience OSA at a rate five times higher than the general population.
• Beckwith-Wiedemann syndrome is a genetic disorder that can cause an enlarged tongue (macroglossia) and abnormal breathing. Children with an enlarged tongue who have not had reduction surgery often experience obstruction of their airway during sleep.
• Congenital central hypoventilation syndrome (CCHS) is a rare genetic disorder that impairs the nervous system’s ability to regulate breathing correctly. Many children receive tracheostomies, mechanical ventilators, and/or diaphragm pacemakers to maintain a normal breathing pattern. Without effective treatment and proper calibration of these assistive breathing devices, children with CCHS experience OSA at a very high rate and may die during sleep.

Lifestyle Risk Factors

Beyond a genetic predisposition and anatomy, there are specific lifestyle risk factors that may worsen the condition. Consider these potential contributions and how they might be avoided:

Weight Gain

As noted above, obesity is a major modifiable risk factor for the development of sleep apnea. It contributes to an increased neck size, fat deposited at the base of the tongue, and decreased lung volumes in sleep. Weight loss may help to alleviate it. As a general rule, losing 10% of the overall body weight may have favorable effects. It is possible for sleep apnea to resolve completely in some individuals.

Alcohol Consumption

Drinking alcohol near bedtime may negatively affect breathing during sleep. It is a known muscle relaxant, and is able to relax the muscles of the airway. Histamines within wine may also lead to nasal congestion. This can worsen both snoring and sleep apnea after alcohol is consumed. It is best to avoid drinking several hours before bedtime to reduce these risks.

Smoking

Smoking irritates the mucosa that lines the airway and this may aggravate snoring and contribute to sleep apnea in susceptible individuals. Nicotine may have further effects that are disruptive to sleep. Smoking cessation may have favorable effects and is encouraged to prevent long-term health consequences.

Vitamin D Deficiency

It is possible that vitamin D deficiency may contribute to sleep disruption and increase the likelihood of experiencing sleep apnea. Further research is needed, but it may be helpful to ensure adequate sunlight exposure, to consume foods containing or fortified with vitamin D, or to take vitamin D supplementation during winter months to prevent deficiency.

Medications

Certain prescription medications may lead to sleep apnea, including muscle relaxants, benzodiazepines, and opioid or narcotic pain medications. It may be important to review the role of medications with a pharmacist or prescribing doctor.

A Word From Verywell

If you suspect you may be experiencing symptoms of sleep apnea, seek evaluation by a board-certified sleep physician. It will be important to review symptoms, undergo a physical examination of the upper airway, and arrange diagnostic testing. If sleep apnea remains untreated it can lead to significant cardiovascular side effects and even premature death.

If sleep apnea is identified, treatments such as CPAP therapy, the use of an oral appliance, position therapy, or weight loss may be very helpful. In some cases, changes in lifestyle may reduce the severity and may ultimately resolve the problem.