Obesity is known to be the primary risk factor for obstructive sleep apnoea (OSA), and a new US study suggests the main risk might be very close to the action.
Researchers from the University of Pennsylvania using magnetic resonance imaging (MRI) to measure the effect of weight loss on the upper airway in obese patients found that reducing tongue fat is a primary factor in lessening the severity of the debilitating condition, which causes breathing to repeatedly stop and start, randomly waking people up.
Richard Schwab and his team had previously discovered that obese patients who suffer from OSA have significantly larger tongues and a higher percentage of tongue fat than those who don’t.
The new study was designed to determine if reducing tongue fat would improve symptoms.
It involved 67 obese participants (body mass index greater than 30) with mild to severe OSA who had lost around 10% of their body weight through dieting and/or surgery over six months. Their OSA scores had subsequently improved by 31% overall.
Schwab and his colleagues scanned each participant’s pharynx and abdomen before and after the weight loss, then used a statistical analysis to quantify changes between overall weight loss and reductions to the volumes of the upper airway structures.
They found that a reduction in tongue fat volume was the primary link between weight loss and OSA improvement.
The study found that weight loss also resulted in reduced pterygoid (a jaw muscle that controls chewing) and pharyngeal lateral wall (muscles on the sides of the airway) volumes.
Both these changes also improved OSA, but not to the same extent as the reduction in tongue fat.
“Now that we know tongue fat is a risk factor and that sleep apnoea improves when tongue fat is reduced, we have established a unique therapeutic target that we’ve never had before,” Schwab says.
One thing they’d like to know now is whether certain low-fat diets are better than others in reducing tongue fat, and whether therapies used to reduce stomach fat might also be applied.
The researchers also are examining new interventions and other risk factors for OSA, including whether some patients who are not obese but who have “fatty” tongues could be predisposed to sleep apnoea, but are less likely to be diagnosed.
Their findings are published in the American Journal of Respiratory and Critical Care Medicine.
In a recent related study, Schwab’s team found that ethnicity may also play a role in sleep apnoea severity.
When they compared the upper airway anatomy of Chinese and Icelandic patients with sleep apnoea, they found that the Chinese had smaller airways and soft tissues, but bigger soft palate volume with more bone restrictions.
This means, Schwab says, that Asian patients may generally be more at risk for severe sleep apnoea symptoms