Non-adjusted posterior tongue adiposity was correlated with isometric but not swallowing tongue strength. That is, greater posterior tongue adiposity was correlated with lower isometric tongue strength. Contrary to our hypothesis, tongue adiposity did not differ as a function of age, gender, or aspiration status.
This is the first study to demonstrate that lower isometric tongue strength is associated with greater tongue adiposity in healthy older adults. This is an important finding, since high levels of adiposity have been linked to decreased physical performance and disability. For example, in the Cardiovascular Health Study, Visser and colleagues reported that high body fat was associated with mobility-related disability and concluded that “high body fatness in old age should be avoided to decrease the risk of disability (p. 584) 16
.” Certainly, increased weight may explain decreased mobility, yet changes in muscle/fat composition ratios may also explain decreased strength and related performance.
Our study demonstrated that higher tongue adiposity was associated with lower isometric tongue strength but not disability (i.e., aspiration status). However, the size of our cohort may have masked possible associations with tongue adiposity and disability/aspiration. Further, the 20 aspirators were healthy adults with intermittent and trace aspiration of liquids only 7
. In patients with dysphagia, tongue adiposity may be correlated with aspiration.
The finding that posterior tongue adiposity was correlated with posterior isometric but not swallowing tongue strength is logical when reviewing the literature on isometric versus swallowing pressures in young vs. older healthy adults. Both Youmans 3
and Nicosia 4
found that isometric
tongue pressure was significantly lower in older versus young adults; but swallowing
tongue pressure was similar between young and older adults. Thus, given swallowing is a sub-maximal strength task, it is reasonable that we did not observe a correlation between tongue adiposity and swallowing tongue strength. However, we previously found, in a larger cohort, that anterior and posterior tongue strength was associated with aspiration status in healthy older adults 11
. Thus, a larger cohort may reveal an association between swallowing tongue pressures and tongue adiposity.
Another possibility is that the ROI used to acquire the posterior tongue pressures coincided with that region of the tongue most heavily recruited to perform the isometric task but not swallowing. Perhaps a different ROI of the tongue may be more closely associated with swallowing pressures and could be evaluated in future investigations.
The finding that tongue adiposity did not vary by gender is somewhat surprising. Barkdull and colleagues found higher tongue adiposity in women compared to men 19
, although unlike our cohort, most of their participants had obstructive sleep apnea. Another likely explanation for a lack of gender effect is that the BMI of our male and female participants were almost identical. An earlier study using autopsy samples found that the percent of posterior tongue fat correlated with BMI in both men and women 18
. Thus, gender, perhaps in association with BMI, may predict tongue fat composition. In the present study, we found no correlation between BMI and tongue fat composition. Earlier, we found no difference in aspiration status relative to BMI 11
. There does appear to be a relationship between isometric and swallowing tongue strength and aspiration status 11
, as well as posterior isometric tongue strength and lingual adiposity. Future duplication of these findings in larger cohorts is needed.
This is the first study to use HUs as acquired via CT scans to assess tongue adiposity as a function of tongue strength and swallowing function. HUs offer a relatively easy way to acquire tongue measures of radiodensity and thus muscle/fat composition, and a previous study demonstrated the use of HUs in tongue adiposity measurements relative to sleep apnea scores 21
. One drawback to this approach is the radiation exposure from the CT scan. Others have used MRI to acquire tongue volume measurements 17,23-26
, and most recently, a method called iterative decomposition of water and fat with echo symmetry and least squares estimation (IDEAL-FSE) to quantify tongue adiposity 17
. It remains to be seen whether HUs via CT scans or IDEAL-FSE methods are the most effective way to measure tongue adiposity. Both are vulnerable to possible interferences from dental artifact; however, CT scans may be most clinically generalizable given their widespread use as part of standard patient care.
Assessing tongue adiposity may provide important insight into the mechanisms of tongue rehabilitation. The tongue is amenable to strength training 23,27-29
, and one study reported increases in tongue volume in a sub-group of four patients following an 8-week tongue exercise program 23
. However, whether the increases in tongue volume were the result of a change in muscle/fat composition is unknown. Further investigation via CT scans would help to identify if change in muscle/fat composition occurs relative to increases in tongue strength.
A possible limitation of this study is that although the identification of aspiration status and tongue strength measures were acquired during the same testing session, there was an approximate six-ten month lapse before the acquisition of the CT scans. However, our previous investigation found that aspiration status in healthy older adults (i.e., aspirator, N=9 and non-aspirator, N=9) remained stable over a one-year period (manuscript in preparation).