Summary: Reduction in tongue fat volume appears to be the key connection between weight loss and improvement in obstructive sleep apnea.
Source: University of Pennsylvania School of Medicine
Weight loss is a well-recognized way to improve symptoms of obstructive sleep apnea (OSA), but the exact mechanism has been uncertain. Researchers at the Perelman School of Medicine, University of Pennsylvania, now report that the decrease in fat within the tongue is a primary factor linking weight loss to better sleep apnea outcomes.
Using magnetic resonance imaging (MRI) to measure changes in upper airway anatomy in people with obesity, the team found that reductions in tongue fat closely tracked improvements in sleep apnea severity. These findings were published in the American Journal of Respiratory and Critical Care Medicine.
“Most clinicians, and even experts in the sleep apnea field, have not typically considered tongue fat as a target for treatment,” said Richard Schwab, MD, chief of Sleep Medicine. “Now that we know tongue fat is a risk factor and that sleep apnea improves when tongue fat is reduced, we have identified a distinct therapeutic target that we did not have before.”
Obstructive sleep apnea affects millions of people and is characterized by repeated pauses in breathing during sleep. These interruptions cause fragmented sleep, loud snoring, and daytime sleepiness, and they increase the long-term risk of hypertension, stroke, and other cardiovascular problems. Obesity is the major risk factor for OSA, but other anatomical contributors—such as enlarged tonsils or a recessed jaw—also play a role. Continuous positive airway pressure (CPAP) therapy remains an effective treatment for many patients, but some people cannot tolerate CPAP and need alternative approaches, which can be more complex.
Previous work by Schwab and colleagues had shown that obese people with OSA tend to have larger tongues and a higher percentage of tongue fat compared with obese individuals without OSA. The new study sought to determine whether lowering tongue fat through weight loss would produce measurable improvements in apnea severity, and to establish a clearer cause-and-effect relationship.
The study enrolled 67 obese adults with mild to severe OSA (body mass index greater than 30.0). Participants underwent an intensive weight loss intervention—either through diet and lifestyle changes or bariatric surgery—and on average lost nearly 10 percent of their body weight over six months. Sleep study measurements showed that participants’ apnea-hypopnea index (AHI), a standard measure of sleep apnea severity, improved by about 31 percent following the weight loss program.
MRI scans of the upper airway and abdomen were performed before and after the intervention. Researchers quantified changes in soft tissue volumes of the upper airway, including tongue fat, pterygoid muscle volume (a jaw muscle important for chewing), and the pharyngeal lateral wall. Statistical analyses were used to link overall weight loss to changes in these structures and to identify which anatomical changes most strongly correlated with improvements in AHI.
The analyses indicated that reduction in tongue fat volume was the primary mediator of the relationship between weight loss and improvement in sleep apnea. While weight loss also reduced volumes of the pterygoid muscles and pharyngeal lateral walls—and those changes were associated with some improvement in OSA—they did not account for as much of the AHI improvement as tongue fat reduction did.
Based on these results, the authors propose that tongue fat represents a promising new therapeutic target for patients with OSA. They suggest future research directions such as investigating whether specific dietary approaches preferentially reduce tongue fat, or whether localized cooling or other procedures used experimentally to reduce fat in other body areas could be adapted for the tongue. Schwab cautions that such targeted interventions have not yet been tested in clinical trials.
Schwab’s team is also exploring additional risk factors and interventions for sleep apnea. One area of ongoing research is whether individuals who are not obese but who have relatively fatty tongues may be predisposed to OSA and could be underdiagnosed because they do not fit the typical high-risk profile.
Related work from the same group suggests anatomical differences between populations may influence OSA severity. In a study comparing Chinese and Icelandic patients matched for age, gender, and symptoms, Chinese patients tended to have smaller upper airways and different soft tissue and bony anatomy that may increase vulnerability to more severe OSA. Schwab emphasizes that clinicians should consider screening for sleep apnea in any patient who reports loud snoring or daytime sleepiness, even if they are not visibly obese, because anatomical risk factors can vary across individuals and populations.
“Primary care clinicians and dental professionals should be asking about snoring and excessive daytime sleepiness routinely,” Schwab said. “Patients with normal body mass index can still have risk factors for sleep apnea and may benefit from evaluation.”
Funding: The study was supported by grants from the National Institutes of Health. Additional authors from the University of Pennsylvania included Stephen H. Wang, Brendan T. Keenan, Andrew Wiemken, Yinyin Zang, Bethany Staley, David B. Sarwer, Drew A. Torigian, Noel Williams, and Allan I. Pack.
Source:
University of Pennsylvania School of Medicine
Media Contacts:
Lauren Ingeno – University of Pennsylvania School of Medicine
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Image credited to University of Pennsylvania School of Medicine.
Original Research: “Effect of Weight Loss on Upper Airway Anatomy and the Apnea Hypopnea Index: The Importance of Tongue Fat.” Stephen H. Wang; Brendan T. Keenan; Andrew Wiemken; Yinyin Zang; Bethany Staley; David B. Sarwer; Drew A. Torigian; Noel Williams; Allan I. Pack; and Richard J. Schwab. Published in the American Journal of Respiratory and Critical Care Medicine (closed access).
Abstract
Effect of Weight Loss on Upper Airway Anatomy and the Apnea Hypopnea Index: The Importance of Tongue Fat
Rationale: Obesity is a leading risk factor for obstructive sleep apnea. Tongue fat is elevated in obese people with OSA and could explain the link between obesity and OSA. Although weight loss improves OSA, the underlying mechanism remained unclear.
Objectives: To determine how weight loss affects upper airway anatomy in people with obesity and OSA. The investigators hypothesized that weight loss would reduce soft tissue volumes, including tongue fat, and that these reductions would correlate with improvements in apnea-hypopnea index (AHI).
Methods: Sixty-seven individuals with obesity and OSA (AHI ≥ 10 events/hour) had sleep studies and upper airway and abdominal MRI scans before and after a weight loss intervention (intensive lifestyle modification or bariatric surgery). Airway dimensions and volumes of soft tissues, tongue fat, and abdominal fat were quantified. Associations between weight loss, anatomical changes, and AHI were analyzed.
Measurements and Main Results: Weight loss was significantly associated with reductions in tongue fat, pterygoid muscle volume, and total lateral wall volume. Reductions in tongue fat correlated strongly with reductions in AHI, and mediation analysis showed that decreased tongue fat volume was the main mediator linking weight loss to AHI improvement.
Conclusions: Weight loss reduced several upper airway soft tissue volumes in people with obesity and OSA, and improvement in AHI was primarily mediated by reductions in tongue fat. Therapies that specifically target tongue fat reduction merit consideration as potential treatments for OSA.