the ability and efficiency of mastication is the first step in the digestion of food , and this ability declines with age ( locker , 2002 ; morley , 2001 ; takata et al . , 2006 ) . masticatory ability is closely associated with maintaining adequate nutrition in older populations ( de morais et al . , 2013 ; kwon , suzuki , kumagai , shinkai , & yukawa , 2006 ; walls , steele , sheiham , marcenes , & moynihan , 2000 ) . lower masticatory ability reduces the variety in a person s diet , leading to malnutrition , weight loss , and a low body mass index ( bmi ) among the older adults ( nordenram , ljunggren , & cederholm , 2001 ; tamura , bell , masaki , & amella , 2013 ) . it is also reported that impairment of mastication is associated with general health status ( miura et al . , 1998 ; miura , araki , & umenai , 1997 ; miura , kariyasu , yamasaki , arai , & sumi , 2005 ; sun et al . , 2007 ) , quality of life ( qol ; brennan , spencer , & roberts - thomson , 2008 ; kimura et al . , 2009 ; takata et al . , 2006 ) , and cognitive function ( elsig et al . , 2015 ; mummolo , ortu , necozione , monaco , & marzo , 2014 ; teixeira et al . , active life expectancy also related chewing ability ( nasu & saito , 2006 ) . impaired masticatory ability often leads to frailty and institutionalization . maintenance or recovery of sufficient chewing ability for older adults is related to a longer active life expectancy . this study investigated whether self - rated masticatory ability is associated with a self - reliant life with adequate subjective health conditions in a community - dwelling older population . the older population in japan is expanding over time and accounts for more than 25% of the population ( i.e. , 32 million ) . the percentage of long - term care recipients above 65 years of age was 17.9% in may 2014 . the gap between life expectancy and active life expectancy is 9.13 years in females and 12.68 years in males , respectively , and this is a pressing issue in japan with increasing older populations , despite the fact that society has achieved the highest level of life expectancy . the extension of active life expectancy constitutes a pivotal issue for not only the well - being of the older population but also the demographics and socioeconomic of the society . this study population consists of participants in survey , which is a prospective and population - based study , and is designed to identify factors for self - reliant life in community - dwelling older adults in japan ( kayama , hironaka , & tani , 2014 ) . this study recruited 1,706 individuals who were 65 years and above , living in kumamoto city , and obtained informed consent from 1,554 of those subjects . those subjects had involvement with regional welfare commission volunteers and community comprehensive care center staffs . the study excluded subjects who died , moved , or were hospitalized during the study , and thus , 1,377 individuals participated ( 459 men and 910 women , mean age 79.8  6.6 years ) . this structured questionnaire survey was conducted in conjunction with regional welfare commission volunteers and community comprehensive care center staffs . the methods for data collection were described previously ( kayama et al . , 2014 ) . subjective health status was established by questionnaire with four levels of choice ; queried items included  very healthy ,   moderately healthy ,   not very healthy ,  and  not healthy . instrumental activity of daily living ( iadl ) was evaluated using an eight - item questionnaire that included walking for 15 min with or without a cane ; going out at least once a week , answering the telephone ; and using home electronic appliances , daily shopping activity , taking trash out , managing money , and ventilating rooms . forgetfulness was queried by the question item :  have you been horribly forgetful lately . daily shopping activity was compared among those living with their family / caregiver and those who did not . daily shopping activity was categorized as supermarket store , convenience store , home delivery , and no shopping . the level of social activity evaluation included attending culture lessons or pursuing a hobby and interacting with neighborhoods . the level of neighborly ties as social capital were evaluated using a questionnaire that asked whether subjects shared any gifts ; had frequent conversations ; usually exchanged greetings ; and rarely interacted with their neighbors . family composition was characterized as living alone , living with spouses , living with family , and spending alone in the daytime . self - rated masticatory ability was measured on a 5-point scale from being able to eat whatever subjects wanted to eat , able to eat most foods except some hard ones , limited foods because of inadequate chewing , unable to eat few foods because of insufficient chewing , and a fluid diet . in this survey , this study was approved by the ethical committee of kumamoto health science university , kumamoto , japan ( no . 23 - 12 for epidemiology ) , and informed content was obtained from all participants . a logistic regression analysis was used to determine which categorical factors were independent predictors of having self - perceived health without requiring long - term care services . a multivariate logistic regression analysis was used to calculate the odds ratios ( ors ) and 95% confidence intervals ( cis ) after controlling simultaneously for potential confounders . all statistical analyses were performed using ibm spss statics for japan version 19.0 for windows ( ibm , japan ) . a value of p < .05 was considered to be statistically significant . this study population consists of participants in survey , which is a prospective and population - based study , and is designed to identify factors for self - reliant life in community - dwelling older adults in japan ( kayama , hironaka , & tani , 2014 ) . this study recruited 1,706 individuals who were 65 years and above , living in kumamoto city , and obtained informed consent from 1,554 of those subjects . those subjects had involvement with regional welfare commission volunteers and community comprehensive care center staffs . the study excluded subjects who died , moved , or were hospitalized during the study , and thus , 1,377 individuals participated ( 459 men and 910 women , mean age 79.8  6.6 years ) . this structured questionnaire survey was conducted in conjunction with regional welfare commission volunteers and community comprehensive care center staffs . the methods for data collection were described previously ( kayama et al . , 2014 ) . subjective health status was established by questionnaire with four levels of choice ; queried items included  very healthy ,   moderately healthy ,   not very healthy ,  and  not healthy . instrumental activity of daily living ( iadl ) was evaluated using an eight - item questionnaire that included walking for 15 min with or without a cane ; going out at least once a week , answering the telephone ; and using home electronic appliances , daily shopping activity , taking trash out , managing money , and ventilating rooms . forgetfulness was queried by the question item :  have you been horribly forgetful lately . daily shopping activity was compared among those living with their family / caregiver and those who did not . daily shopping activity was categorized as supermarket store , convenience store , home delivery , and no shopping . the level of social activity evaluation included attending culture lessons or pursuing a hobby and interacting with neighborhoods . the level of neighborly ties as social capital were evaluated using a questionnaire that asked whether subjects shared any gifts ; had frequent conversations ; usually exchanged greetings ; and rarely interacted with their neighbors . family composition was characterized as living alone , living with spouses , living with family , and spending alone in the daytime . self - rated masticatory ability was measured on a 5-point scale from being able to eat whatever subjects wanted to eat , able to eat most foods except some hard ones , limited foods because of inadequate chewing , unable to eat few foods because of insufficient chewing , and a fluid diet . in this survey , this study was approved by the ethical committee of kumamoto health science university , kumamoto , japan ( no . 23 - 12 for epidemiology ) , and informed content was obtained from all participants . a logistic regression analysis was used to determine which categorical factors were independent predictors of having self - perceived health without requiring long - term care services . a multivariate logistic regression analysis was used to calculate the odds ratios ( ors ) and 95% confidence intervals ( cis ) after controlling simultaneously for potential confounders . all statistical analyses were performed using ibm spss statics for japan version 19.0 for windows ( ibm , japan ) . a value of p < .05 was considered to be statistically significant . the initial evaluation of the participants ( 1,377 individuals ) in the present study showed that 578 subjects could eat whatever they wanted to eat , 686 could eat most foods except a few that were difficult , 83 could eat a limited number of foods because of insufficient chewing ability , 6 could eat few foods because most were too difficult to chew , and 3 were on a fluid diet . participants who answered  unknown  ( 21 persons ) were excluded from the current statistical analysis . the association between the subjects self - rated masticatory ability with having good self - perceived health without requiring long - term care as a self - reliant life among the older adults is shown in table 1 . the population that could chew whatever they wanted to eat included the highest proportion ( 68.6% ) of those having good self - rated health without requiring long - term care ( p < .001 ,  test ) , and only 6.2% of those with poor self - rated health and requiring long - term care insurance were found in this population . in contrast , the population that could eat a limited number of foods because of insufficient chewing ability accounted for 56.6% of those with poor self - rated health and requiring long - term care . association of self - rated masticatory ability with self - reliant life in older adults . note . category numbers of mastication are as follows : 1 = whatever wanting to eat , 2 = most foods expect some hard ones , 3 = limited foods because of chewing not well , 4 = few foods because of the difficulty of chewing or fluid diet . the association between self - rated masticatory ability with other characteristics of the participants is shown in table 2 . the group with adequate self - rated masticatory ability included a younger population ( 65 - 74 , 53.2% ) than the other groups ( 75 - 84 , 43.0% ; above 85 , 32.7% ) . the group having a bmi < 18.5 included a significantly lower proportion of those with good mastication . the characteristics associated with mastication were walking for 15 min ; anxiety about falling ; going out once or more per week ; becoming forgetful ; using the telephone availing electronic appliance ; daily shopping ; taking the trash out ; managing money ; having a hobby ; interacting with neighbors ; and sharing with neighbors . in addition , having good self - rated health and not requiring long - term care with good subjective health was also significantly associated with the subjects self - rated masticatory ability ( p < .001 ,  test ) . association between self - rated masticatory ability with demographic , nutritional , status , iadl items , and self - reliant life in elderly . note . data was analyzed by chi - square test ( having good self - rated masticatory ability vs. rest of all ) . self - reliant life with good subjective health : having good self - perceived health without receiving long - term care insurance . the ors and 95% cis for having good self - rated health without receiving long - term care insurance were calculated using a logistic regression analysis adjusted for multiple confounding factors , such as demographics , iadl , social capital , cognitive function , and self - rated masticatory ability ( table 3 ) . an unadjusted univariate analysis revealed that better mastication , younger age , better iadl ( walking for 15 min , going out once and over a week , using the telephone , using home electronic appliances , going to shopping daily , taking the trash out , managing money , and ventilating rooms ) , good social capital ( having a hobby , interaction with neighbors ) , and better cognitive function ( not forgetful ) were associated with good self - rated health without receiving long - term care . the crude or for mastication was 3.47 ( 95% ci = [ 2.76 , 4.38 ] ) . model 1 adjusted for age and gender attenuated the or for mastication but remained statistically significant ( or = 3.26 , 95% ci = [ 2.58 , 4.13 ] ) . model 2 , adjusted for iadl , social capital , and cognitive function , and the or for mastication , was still statistically significant ( or = 2.16 , 95% ci = [ 1.64 , 2.83 ] ) . association of self - reliant later life with self - rated masticatory ability determined by multilevel logistic regression . note . or = odds ratio ; ci = confidence interval . the participants were divided into four groups based on their self - rated masticatory ability and self - reliant life , and the number of iadl items ( eight items maximum ) in each group were analyzed ( figure 1 ) . a multiple anova adjusted for gender and age revealed that there were significantly more iadl items in individuals having good mastication ( 7.64  0.84 ) than those without good mastication ( 7.32  1.28 ) even among those with self - rated good health who were not receiving long - term care . similarly , there were significantly more iadl items in the individuals having good mastication ( 6.55  1.71 ) than in those who did not ( 5.44  2.19 ) , even in the group that did not have good self - rated health and were not receiving long - term care . comparison of number of iadl items for the four groups by self - perceived masticatory ability and health . the word , in figure ,  health  indicates self - perceived health without receiving long - term care insurance , and  mastication the current study found that self - rated masticatory ability was significantly associated with the self - perceived good health in those not receiving long - term care insurance in community - dwelling age of 65 and above . the self - perceived good health in subjects who were not receiving long - term care insurance defined those with a self - reliant later life . the present study is the first report on the relationship between a self - reliant later life with positive self - perceived health and self - rated masticatory ability . the significant association between the subjects self - rated masticatory ability and their self - perceived good health without receiving long - term care insurance indicated that satisfactory masticatory ability could be an independent predictor of a self - reliant later life . rising a rate of long - term institutionalization of older adults damages both the sustainability of social security and the aged own qol . health , labour , and welfare ministry in japan estimated a reduction in health care cost would be 8.9 billion dollar per year in 2020 , if increase in active life expectancy would exceed increase in total life expectancy . to maintain their active life and to live in their familiar environment until the end of the life without institutionalization or hospitalization , it is critical to expand active life expectancy . in addition , multiple lines of evidences demonstrated that life expectancy crucially related with the self - perceived health ( kaplan & camacho , 1983 ; larue , bank , jarvik , & hetland , 1979 ; rakowski , mor , & hiris , 1994 ) . taken together , we defined the aged self - reliant status as self - perceived adequate health without long - term care - required certification . the current findings are consistent with those of previous studies reporting the relationship between patients qol and their masticatory ability . a previous study found that poor chewing ability based on the number of chewable foods was significantly associated with poor qol status in 80-year - old subjects ( takata et al . , 2006 ) . miura et al . ( 2000 ) reported that satisfactory chewing status is correlated with qol evaluated by the total score of the philadelphia geriatric center ( pcg ) morale . a report on older brazilians showed that those satisfied with their ability to chew food was closely correlated with the score of each domain ( physical , psychological , environment , and social relations ) on the world health organization quality of life questionnaire - brief version ( hugo , hilgert , de sousa mda , & cury , 2009 ) . another recent study reported a relationship between certification of long - term care insurance and self - rated chewing ability . the result of the kaplan  meier analysis for individuals aged 65 to 79 years clearly demonstrated that the proportion of individuals not certified for long - term care insurance significantly declines in those with self - rated fair or poor masticatory ability compared with those having good mastication ( moriya , notani , murata , inoue , & miura , 2014 ) . a cox proportional hazard analysis also shows that the certification for long - term care insurance was 1.87-fold ( ci = [ 1.07 , 3.27 ] ) higher in the individuals with fair or poor masticatory ability in comparison with those with adequate ability ( moriya et al . , 2014 ) . a 6-year follow - up study on rural community  dwelling older adults in japan by shinkai et al . ( 2003 ) demonstrated that depression of basic activity of daily living ( adl ) and iadl were 1.88-fold ( ci = [ 1.26 , 2.82 ] ) and 2.22-fold ( ci = [ 1.50 , 3.27 ] ) , respectively , higher in individuals with poor chewing ability in comparison with those with better ability . taken together , maintaining the chewing ability in later life would advantage self - reliant life through keeping well both mentally and physically . these evidences suggest that masticatory ability should be the concern in gerontological research . to ensure sustainability of social security system , it is important to close the gap between life expectancy and active life expectancy . ( 2011 ) conducted a study of 882 individuals aged 65 and above , and a multivariate logistic regression demonstrated that severely impaired masticatory ability is significantly related to higher hospitalization costs . kimura et al . ( 2013 ) assessed masticatory efficiency using color - changing chewing gum in 269 community - dwelling japanese older adults above the age of 75 , and concluded that lower masticatory efficiency is significantly associated with lower adl , lower cognitive function , and depression . the result of panel interview surveys for age of 65 and above in japan indicated that active life expectancy of individuals who could chew relatively hard foods was 2 to 3 years longer than people who could chew only relatively soft foods in daily diet ( nasu & saito , 2006 ) . these evidences , including our findings , strongly suggested that maintenance of adequate chewing ability in older adults is closely related to expansion of the active life expectancy , leading to the sustainability of social security system . the participants of the current study were armed with a regional welfare commission volunteer or community comprehensive care center . therefore , the proportion of participants receiving long - term care insurance in the present study was 33.8% , higher than the average proportion in japan ( 17.9% in aged 65 and above ) . the proportion of participants whose health was perceived to be well was 67.2% , slightly lower than a population based on a recent survey on health consciousness by the ministry of health , labour , and welfare in japan ( 77.9% in aged 65 years and above in 2014 ) . this study conducted a structured - questionnaire interview - based investigation in conjunction with the regional commission volunteers or public nurses on the staffs of community comprehensive care center , closely interacting with community - dwelling older adults through regular home visits . therefore , the volunteers or the public nurses commissioned this investigation had built a good rapport with the participants in the study , allowing them to collect true - to - life data . the self - rated masticatory ability was closely correlated with neighborhood social capital , such as interacting with neighbors and sharing something with neighbors , as shown in table 2 . results from a prospective cohort study based on the aichi gerontological evaluation study indicated that both community and individual levels of horizontal social capital ( such as volunteer group , sports clubs , and hobby clubs ) are significantly associated with retaining 20 or more teeth in individuals aged 65 and above ( aida et al . , 2009 ) . conducted another study based on a survey in ohsaki city and demonstrated that neighborhood social capital , accomplished by four kinds of networks ( civic , sports and hobby , volunteer , and friendship networks ) , is closely correlated with dentate status in older adults ( aida et al . , in contrast , social capital is not correlated with the use of oral prosthesis , such as a denture or dental bridge ( yamamoto et al . , 2014 ) . there were few questionnaire items to measure social capital in the current study ; thus , conclusions based on the relationship between social capital and masticatory ability were limited . further study on the association between social capital and masticatory ability is needed . first , self - rated masticatory ability has not correlated with any objective masticatory function such as bite force . this may weaken our argument , although there are multiple evidences on good correlation between subjective and objective chewing ability . second , participants of this study were selected by regional welfare commission volunteers and community comprehensive care center staffs , suggesting to have bias . further study is needed to assess the community - dwelling elderly people who have no relation with regional welfare commission volunteers or community comprehensive care center staffs . third , we did not have any socioeconomic status , such as income and length of educations , of participants . although society in kumamoto area narrowed the gap between the rich and the poor in older adults , subjective masticatory ability may be related with socioeconomic status in japanese older adults . fourth , there is a geographic limitation , as the participants were all from one city . some clinical data , such as serum albumin level for nutrition condition or blood pressure for general condition , might strengthen our findings . sixth , to ensure this mechanism , effect of clinical intervention on masticatory ability , such as denture wearing , dental implant , and muscle training , would be a considerable research task . in conclusion , there was a significant association between self - rated masticatory ability and having self - perceived good health in older adults who were not receiving long - term care insurance , suggesting that a satisfactory level of chewing could be an independent predictor for self - reliant living in the community - dwelling older population . the result of our study demonstrated that asking the self - rated masticatory ability could be an easier and a useful tool for non - healthcare professionals to assess the health status of regional older adults . first , self - rated masticatory ability has not correlated with any objective masticatory function such as bite force . this may weaken our argument , although there are multiple evidences on good correlation between subjective and objective chewing ability . second , participants of this study were selected by regional welfare commission volunteers and community comprehensive care center staffs , suggesting to have bias . further study is needed to assess the community - dwelling elderly people who have no relation with regional welfare commission volunteers or community comprehensive care center staffs . third , we did not have any socioeconomic status , such as income and length of educations , of participants . although society in kumamoto area narrowed the gap between the rich and the poor in older adults , subjective masticatory ability may be related with socioeconomic status in japanese older adults . fourth , there is a geographic limitation , as the participants were all from one city . some clinical data , such as serum albumin level for nutrition condition or blood pressure for general condition , might strengthen our findings . sixth , to ensure this mechanism , effect of clinical intervention on masticatory ability , such as denture wearing , dental implant , and muscle training , would be a considerable research task . in conclusion , there was a significant association between self - rated masticatory ability and having self - perceived good health in older adults who were not receiving long - term care insurance , suggesting that a satisfactory level of chewing could be an independent predictor for self - reliant living in the community - dwelling older population . the result of our study demonstrated that asking the self - rated masticatory ability could be an easier and a useful tool for non - healthcare professionals to assess the health status of regional older adults .