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When patients with obstructive sleep apnea (OSA) show symptom relief from weight loss, it may be from fat reduction in one relatively small part of the body, researchers suggested.

OSA patients in the 67-person study who lost, on average, around 10% of their body weight over 6 months through either diet or weight-loss surgery showed improvements in Apnea/Hypopnea Index (AHI) score, which is the leading measure of OSA severity, according to Richard J. Schwab, MD, of the University of Pennsylvania Perelman School of Medicine in Philadelphia, and colleagues.

And about 30% of that improvement was attributable to reduced tongue fat, they reported in the .

The study, which identified tongue fat reduction as a key mechanism in weight-loss associated OSA improvement, could lead to novel strategies for prevention and treatment of the sleep disorder, Schwab told 番茄社区app.

"If you lose weight, AHI improves, and this study showed that the primary factor mediating that is a reduction in tongue fat," he said, explaining that while obesity is a key risk factor for OSA, and weight loss is well recognized as an effective treatment strategy, the mechanism or mechanisms driving this are not well understood.

Earlier research by Schwab and colleagues described an increased tongue fat volume in obese OSA patients versus obese people without OSA. included 90 obese patients with OSA and 31 obese patients without OSA, and the tongues of people with OSA were found to be significantly larger and with more more fat than the obese people without OSA.

Schwab told 番茄社区app while weight loss may be effective for reducing tongue fat, other treatments that do not depend on losing weight could also prove effective, such as performing exercises that strengthen tongue muscles, which have been shown in some studies to reduce OSA severity, possibly by reducing tongue fat.

It is also possible that therapies aimed at targeted fat removal, such as , may prove to be useful in patients with OSA, he noted.

Schwab said the next step is to examine whether these and other techniques could be effective OSA therapies. The researchers are also examining whether ultrasound can effectively identify tongue size and tongue fat in large populations.

"If we can show that [ultrasound] can do this, we can potentially do it on every person who has a sleep study to get a lot of data on the effect of tongue size and tongue fat, and its relationship to OSA," he said.

The primary goal of the current study was to further examine changes in upper airway anatomy associated with weight loss in patients with OSA to better understand how these changes improve OSA symptoms.

Study participants underwent lifestyle modification for weight loss (n=49) or bariatric surgery (n=18). Among the latter patients, eight patients had gastric sleeve surgery, nine had Roux-en-Y gastric bypass, and one had gastric banding.

Standard polysomnography and MRI studies were conducted before and after the weight-loss intervention. Imaging was used to assess 10 measures of airway size, including airway volume and average cross-sectional area.

MRI was also used to examine 12 measures of soft tissue volume, including tongue, tongue fat, soft palate, para-pharyngeal fat pads, lateral walls, pterygoids, epiglottis, and combined soft tissue volume. Total, subcutaneous, and visceral abdominal fat volumes also were examined.

Participants (mean age 49) had an average BMI of 42.6. They lost an average of 9.5% of their body weight (P<0.0001) and AHI improved by 30.7% (P=0.0004).

OSA patients who lost 2.5% or more of their total body weight showed significant AHI reductions (-23.3, P<0.0001) compared with no change in those who did not lose weight.

To understand how weight loss affected the upper airway and abdominal fat, the researchers assessed Pearson's correlations between percent changes in weight and anatomical structures.

"Among soft tissue measures, greater percentage decreases in tongue fat were associated with larger reductions in AHI (partial rho = 0.62, P<0.0001), controlling for clinical covariates," they wrote. "This result remained nominally significant also controlling for weight change (partial rho = 0.36; P=0.014), suggesting reduced tongue fat is independently associated with reduced AHI."

The findings may help explain why surgery done to reduce the size of the tongue, known as coblation, has not proven very effective for the treatment of OSA, Schwab said.

Coblation involves the use of radiofrequency and water to vaporize soft tissue, but the treatment does not discriminate between tongue muscle and tongue fat.

The current study results demonstrating a specific role for tongue fat volume could explain the poor treatment performance. "If only fat tissue was removed, coblation could be more effective. Future studies are warranted to study this," the authors explained.

Study limitations included the use of MRI at multiple time points, such that anatomic changes may have reflected differences in positioning during imaging rather than the effect of weight loss alone. Also, the study included medical and surgical weight loss.

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