Relationship between Masseter Muscle Thickness and Skeletal Muscle Mass in Elderly Persons Requiring Nursing Care in North East Japan

Maintenance and improvement of masticatory function in nursing care elderly persons (NC) is an important issue, and it is speculated that sarcopenia is related to declining masticatory function. The decrease in skeletal muscle index(SMI), a major diagnostic criterion for sarcopenia, has been reported to be associated with swallowing function in NC.However, the relationship between SMI and masticatory function is unknown. Therefore,we investigated the relationship between masseter muscle thickness(MMT)and SMI, with the aim of examining the specific relationship between decreased masticatory function and sarcopenia in NC. MMT and SMI were measured by ultrasonography and bioelectrical impedance analysis in 275 NC participants in Omori Town, Yokote City, Akita Prefecture in the Tohoku region in Japan. Cognitive functions measured from all participants using questionnaire. Participants were classified into low-MMT or high-MMT group based on the median of each of MMT, and SMI and related items in each gender. In addition, to examine the factors related to MMT, logistic regression analysis was conducted by entering age,sex, SMI, nutrition status, severity of dementia, and other items as explanatory variables and MMT as objective variable. SMI in high-MMT group were significantly higher than low-MMT group(high-MMT: 4.8±1.4 kg/m2, low-MMT: 4.4±1.4 kg/m2, P=0.010).Furthermore, logistic regression analysis indicated that SMI were significantly associated with a MMT(Odds Ratio=0.83, 95% Confidence Interval=0.69-0.99, P=0.049). Our result suggested that the mass of the masseter muscles decreased with NC due to sarcopenia, possibly contributing to a decrease in masticatory function.