Are Sleep Apnea, Hypertension and Gut Bacteria Linked?

What is Sleep Apnea? 

Sleep apnea is a condition where an individual stops breathing for periods throughout the night. Obstructive sleep apnea (OSA), the most common form, occurs when throat muscles temporarily relax and block the airways. 

Central apnea, which is relatively rare, occurs when the brain does not send appropriate signals to the muscles engaged in breathing. The issue here lies within the central nervous system, rather than a physical obstruction of the airway.

OSA affects an estimated 22% of men and 17% of women. If undetected, it can increase the risk of developing heart disease and depression.

Sleep-related breathing disorders are common, with an estimated prevalence of 10% to 30%. In addition to symptoms of excessive daytime sleepiness and decline in cognitive functions, obstructive sleep apnea is well known to be related to many comorbidities, including cardiovascular disorders, endocrinologic disorders, neurologic disorders, hematologic disorders and cancer, leading to an increased morbidity and mortality. 

What is Hypertension? 

Hypertension or high blood pressure is a common condition in which the long term force of the blood against the artery walls is high enough that it may eventually cause health problems, such as heart disease. 

Hypertension needs no introduction. It is even more prevalent than sleep apnea, affecting nearly half of adults in the United States. Worldwide, high blood pressure affects around 1.28 billion people aged 30–79. OSA is common in individuals with drug-resistant hypertension.

Research suggests that there is a dose-dependent relationship between sleep-disordered breathing and hypertension. In other words, individuals with more severe breathing difficulties at night have an increased risk of developing hypertension. 

Scientists are still exploring the mechanisms involved in the link between OSA and hypertension. Multiple pathways are likely, but some researchers believe that the gut microbiome might play a role.

Gut Microbiome 

Human microbiota refers to the comprehensive and exhaustive collection of microbes living in a specific organ of the human body (eg, skin, oral cavity, gut). These microbes include bacteria, viruses, fungi, and parasites, with bacteria being the most common microbes that have been identified. The gut harbors the largest proportion of the microbiota, with more than 100 trillion bacteria from more than 1,000 species.

The human body has its own microbiota and ecosystem generating a unique fingerprint of that individual, but rather than being one that is rigid and fixed; it is dynamic and modifiable.

The microbiota starts to develop in utero and rapidly evolves during infancy and early childhood to acquire its unique individual signature. 

This equilibrium and overall stability of the microbiota ecosystem are considered as a critical contributor to maintaining health, but many external factors can alter the gut microbiota and introduce more harmful species.

How Disordered Breathing Can Influence Gut Microbiome? 

A review study published in the Journal of Clinical Sleep Medicine outlines one theory as to how disordered breathing during sleep might influence bacterial populations. 

Sleep apnea causes intermittent hypoxia or low levels of oxygen in the blood through the night. This hypoxia produces periodic decreases in the partial oxygen pressure gradient inside the tubes of the gastrointestinal system. Bacteria that can only grow in low oxygen environments (obligate anaerobes) and those that can thrive with or without oxygen (facultative anaerobes) get a boost. 

The trials that were evaluated confirmed that intermittent hypoxia models resulted in gut dysbiosis, which can cause a state of low-grade inflammation through damage to the gut wall barrier resulting in “leaky gut.” Neuroinflammation is a hallmark of the pathophysiology of Obstructive sleep apnea-induced hypertension. 

The study notes an abundance of Firmicutes and a reduction in Bacteroidetes and Proteobacteria compared with control mice. An increase in Firmicutes with a reduction in Bacteroidetes is considered a hallmark of dysbiosis.

A damaged intestinal epithelium or “leaky gut” allows increased traffic from the gut into the blood. Compounds that the gut would normally trap and excrete from the body can now enter the blood and travel to distant organs and systems. Once they are in circulation, the body mounts a low-grade inflammatory response. Here, finally, we meet the intersection of OSA, gut bacteria, and hypertension.

To summarize, intermittent hypoxia experienced during the night disturbs the microbiome. This bacterial disturbance makes the gut epithelium leaky and allows toxins to leach into the blood. This sparks inflammation and, therefore, increases the risk of hypertension and other cardiovascular problems.

Another study using fecal transplantation generated surprising results. Scientists mimicked OSA in mice using intermittent hypoxia for 6 weeks and as they expected there were changes in the gut microbiome. After that, they extracted feces from the OSA mice and transplanted the fecal slur into naive mice that had been sleeping normally.

They found that their sleep patterns had changed and that now they slept for longer and were more likely to sleep during the dark cycle, a time when they would normally be active. 

The authors concluded that sleep disturbances can be mediated, at least in part by intermittent hypoxia-induced alterations in gut microbiomes. In other words, the sleep disturbance disrupts the gut microbiome and these disturbed populations of gut bacteria can also disturb sleep patterns. 

Source: 

Mashaqi S, Gozal D. Obstructive sleep apnea and systemic hypertension: gut dysbiosis as the mediator? J Clin Sleep Med. 2019;15(10):1517–1527. 

Tim Newman (2021, Oct 16). Hypertension, gut bacteria, and sleep apnea: Is there a link? Medical News Today. Retrieved from:
https://www.medicalnewstoday.com/articles/hypertension-gut-bacteria-and-sleep-apnea-is-there-a-link

Image from: 

https://www.everydayhealth.com/sleep/how-do-the-bacteria-in-my-gut-affect-my-sleep/