the number of aging workers among the working population is increasing , leading to significant economic and public health challenges worldwide . the main reasons are increasing life expectancy , decreasing birth rates , and the large " baby boomer " generation born after world war ii getting old . the international labour organization has estimated that by the year 2025 , the proportion of the working population aged more than 55 years will be 21% in asia , 32% in europe , 30% in north america , and 17% in latin america . the impact of these changes is currently being felt most strongly in developed countries , making it important for these countries to extend workers ' working life expectancy ( wole ) in order to maintain labor force participation . furthermore , among older people , losing or leaving one 's occupation is associated with a negative impact on both socioeconomic and health status . thus , over 75% of aging workers choose to continue working , even if they develop a significant work disability . an investigation to assess wole among aging workers is thus warranted . unfortunately , the aging process places burdens on health that may cut working life short . workers ' self - perceived health status deteriorates with age , and chronic diseases ( including hypertension , diabetes , and liver disease ) are more common in older people than in the middle - aged population . pain is especially common in older workers worldwide ; for instance , a longitudinal study in the us ( 1992 - 2008 ) found that the prevalence of persistent back pain among construction workers aged more than 50 years to be about 40% . poor health may lead to poor work performance , and both are important factors in early exits from working life . indeed , many older workers with pain experience significantly decreased work performance or find themselves unable to participate in the labor force , and pain is associated with poor health status on both self - reported and external - observer assessments , as well as with work disability . pain thus poses a key obstacle to maintaining wole in older workers ; however , its impact on work has not been studied in detail , particularly given that aging workers will soon be among our main human resources . no study has yet comprehensively addressed the relationship between pain and the risk of early discontinuation of working life . therefore , we explored the relationship between pain and wole scale ( woles ) among korean workers aged 55 or older , using data from the korean longitudinal study of ageing ( klosa ) , by undertaking a multivariate analysis of participants ' demographic characteristics and chronic disease status . we used data from the 2012 phase of klosa , conducted by the korea labour institute and the korea employment institute information service . klosa began in 2006 with surveys and interviews of 10,254 randomly selected adults aged 45 or older who were residing in one of 15 city - size administrative areas based on the population and housing census as a sampling frame to represent citizens in the republic of korea . other countries ' elderly panel surveys are conducted in those older than 50 years old . by the late 1990s currency crisis in korea , thus , klosa expanded the survey target population to over 45 years old to give consideration to social circumstances in korea . of the original respondents , 7,486 were able to participate in the fourth phase of the survey , conducted from july to december 2012 . participants were interviewed using computer - assisted personal interviewing , where the professional interviewers instructed respondents to read the questions on a computer and input their answers directly . for analysis purposes , we treated the 2012 phase as a cross - sectional study . previous studies have divided the older population into three categories : ( 1 ) young - old ( 65 to 74 ) , ( 2 ) middle - old ( 75 to 84 ) and ( 3 ) oldest - old ( older than 85 ) . however , those older than 75 years of age are prone to frailty and rapid deterioration in physical and mental health status . to reduce the possibility of our woles data being confounded by such factors , we excluded participants aged more than 75 years from our study , along with those who were economically inactive ( combined n=4,754 ) . hence , we also excluded those diagnosed with cancer within 6 years after beginning the klosa ; this condition is closely associated with pain , with significant pain occurring in approximately 33%-66% of cancer patients . finally , we excluded subjects who had any missing data . the final sample included 1,979 participants ( 1,175 men and 804 women ) ( fig . interviewers provided information about research objectives and potential risks and benefits to all survey respondents before they answered any questions . all respondents also agreed to participate in further scientific research . to define the wole status , the participants ' expectation of maintaining the current job was assessed by self - reported questionnaires . the statement was " i can keep working in this job for 5 more years " for economically active participants . participants were asked to answer this question using a visual analogue scale ( 0 to 100 with intervals of 10 , where 0 signified " never " or " it will never happen to me " and 100 signified " always " or " it will happen to me sure as fate " ) . workers who had scores of 50 or higher were defined as the higher - woles group , while others were defined as the lower - woles group . participants were provided with a list of body parts ( head , shoulder , arm , wrist , finger , chest , abdomen , waist , hip , leg , knee , ankle , and toe ) and asked whether they suffered pain at any of these sites . we re - grouped thirteen pain sites into five according to the human anatomical system : head , upper extremes ( shoulder , arm , wrist , and finger ) , chest & abdomen , back & lumbar ( waist and hip ) , and lower extremes ( leg , knee , ankle , and toe ) . if participants answered yes for any site , they were asked to indicate the severity of their pain ( mild , moderate , or severe ) . we divided respondents into four groups according to the number of sites at which they had pain ( 0 , 1 , 2 , 3 ) , as the effects of pain worsen with increasing number of pain sites . respondents were also grouped by total pain severity , which was answered by pain severity for each site ( mild , moderate , and severe ) ; total pain severity categories included " none , " " mild , " " moderate , " and " severe . " we used klosa data on age , gender , monthly household income , education level , marriage status , physical activity level , smoking status , drinking status , population of region of residence , history of chronic disease , and history of traffic accidents . monthly household income was self - reported and measured in us dollars , with categories including < $ 1,000 , $ 1,000~2,000 , $ 2,000~$3,000 , and $3,000 . marriage status was also self - reported , but we reorganized the data into two categories , " living with spouse " and " living alone , " with the latter including respondents who were divorced , widowed , separated , or never married . occupational classifications were regrouped into four of the ten major categories of the international standard classifications of occupations , according to skills and duties : white collar workers ( managers , professionals , technicians , and associate professionals ) , pink collar workers ( clerical support , service , and sales workers ) , green collar workers ( skilled agricultural , forestry , and fishery workers ) , and blue collar workers ( crafts and related trades , plant and machine operators and assemblers , and elementary occupations ) . types of employment were categorized as paid , self - employed , and unpaid family worker . paid workers were grouped according to working status into three categories : permanent , temporary , and daily employee . job satisfaction level was self - reported , including satisfaction and dissatisfaction . regarding physical activity level , regular exercise was defined as exercise more than once per week with each session lasting at least half an hour . smoking status and drinking status were categorized as " current , " " past , " or " never . " regions of residence were divided into three categories according to population size : rural areas ( less than 50,000 ) , cities ( more than 50,000 ) , and metropolitan cities ( more than 1 million ) . questions about history of traffic accidents within 6 years of the beginning of klosa were asked because such accidents are a common risk factor for pain in older workers . chronic diseases can also lead to work disability in the older population ; among our respondents , chronic diseases clinically diagnosed within 6 years of the beginning of klosa included hypertension , diabetes , bronchiolitis , emphysema , liver diseases ( excluding fatty liver ) , myocardial infarction , angina , heart failure , depression , anxiety , insomnia , excessive stress , senile psychosis , and others . according to the status of woles , the frequency and mean with standard deviation were calculated for each data category , and the chi - squared test was used to evaluate the association between categories . multiple logistic regression models were then used to calculate odds ratios ( ors ) and 95% confidence intervals ( 95% cis ) for the lower - woles group in relation to the number of sites where participants experienced pain and total pain severity . the multiple logistic models were adjusted for age , sex , household income , marriage status , residence , occupational classification , type of employment , working status , job satisfaction level , health behavioral factors such as smoking , drinking , and physical activity , chronic diseases ( hypertension , diabetes , chronic lung disease , liver disease , and cardiovascular disease ) , and history of traffic accidents . statistical analyses were performed with sas ( version 9.4 , sas institute , cary , nc , usa ) . a p value < 0.05 was considered to indicate statistical significance in both tails . we used data from the 2012 phase of klosa , conducted by the korea labour institute and the korea employment institute information service . klosa began in 2006 with surveys and interviews of 10,254 randomly selected adults aged 45 or older who were residing in one of 15 city - size administrative areas based on the population and housing census as a sampling frame to represent citizens in the republic of korea . other countries ' elderly panel surveys are conducted in those older than 50 years old . by the late 1990s currency crisis in korea , thus , klosa expanded the survey target population to over 45 years old to give consideration to social circumstances in korea . of the original respondents , 7,486 were able to participate in the fourth phase of the survey , conducted from july to december 2012 . participants were interviewed using computer - assisted personal interviewing , where the professional interviewers instructed respondents to read the questions on a computer and input their answers directly . for analysis purposes , we treated the 2012 phase as a cross - sectional study . previous studies have divided the older population into three categories : ( 1 ) young - old ( 65 to 74 ) , ( 2 ) middle - old ( 75 to 84 ) and ( 3 ) oldest - old ( older than 85 ) . however , those older than 75 years of age are prone to frailty and rapid deterioration in physical and mental health status . to reduce the possibility of our woles data being confounded by such factors , we excluded participants aged more than 75 years from our study , along with those who were economically inactive ( combined n=4,754 ) . hence , we also excluded those diagnosed with cancer within 6 years after beginning the klosa ; this condition is closely associated with pain , with significant pain occurring in approximately 33%-66% of cancer patients . finally , we excluded subjects who had any missing data . the final sample included 1,979 participants ( 1,175 men and 804 women ) ( fig . interviewers provided information about research objectives and potential risks and benefits to all survey respondents before they answered any questions . to define the wole status , the participants ' expectation of maintaining the current job was assessed by self - reported questionnaires . the statement was " i can keep working in this job for 5 more years " for economically active participants . participants were asked to answer this question using a visual analogue scale ( 0 to 100 with intervals of 10 , where 0 signified " never " or " it will never happen to me " and 100 signified " always " or " it will happen to me sure as fate " ) . therefore , higher scores indicated a greater expectation of maintaining a current job . workers who had scores of 50 or higher were defined as the higher - woles group , while others were defined as the lower - woles group . participants were provided with a list of body parts ( head , shoulder , arm , wrist , finger , chest , abdomen , waist , hip , leg , knee , ankle , and toe ) and asked whether they suffered pain at any of these sites . we re - grouped thirteen pain sites into five according to the human anatomical system : head , upper extremes ( shoulder , arm , wrist , and finger ) , chest & abdomen , back & lumbar ( waist and hip ) , and lower extremes ( leg , knee , ankle , and toe ) . if participants answered yes for any site , they were asked to indicate the severity of their pain ( mild , moderate , or severe ) . we divided respondents into four groups according to the number of sites at which they had pain ( 0 , 1 , 2 , 3 ) , as the effects of pain worsen with increasing number of pain sites . respondents were also grouped by total pain severity , which was answered by pain severity for each site ( mild , moderate , and severe ) ; total pain severity categories included " none , " " mild , " " moderate , " and " severe . " we used klosa data on age , gender , monthly household income , education level , marriage status , physical activity level , smoking status , drinking status , population of region of residence , history of chronic disease , and history of traffic accidents . monthly household income was self - reported and measured in us dollars , with categories including < $ 1,000 , $ 1,000~2,000 , $ 2,000~$3,000 , and $3,000 . marriage status was also self - reported , but we reorganized the data into two categories , " living with spouse " and " living alone , " with the latter including respondents who were divorced , widowed , separated , or never married . occupational classifications were regrouped into four of the ten major categories of the international standard classifications of occupations , according to skills and duties : white collar workers ( managers , professionals , technicians , and associate professionals ) , pink collar workers ( clerical support , service , and sales workers ) , green collar workers ( skilled agricultural , forestry , and fishery workers ) , and blue collar workers ( crafts and related trades , plant and machine operators and assemblers , and elementary occupations ) . types of employment were categorized as paid , self - employed , and unpaid family worker . paid workers were grouped according to working status into three categories : permanent , temporary , and daily employee . job satisfaction level was self - reported , including satisfaction and dissatisfaction . regarding physical activity level , regular exercise was defined as exercise more than once per week with each session lasting at least half an hour . smoking status and drinking status were categorized as " current , " " past , " or " never . " regions of residence were divided into three categories according to population size : rural areas ( less than 50,000 ) , cities ( more than 50,000 ) , and metropolitan cities ( more than 1 million ) . questions about history of traffic accidents within 6 years of the beginning of klosa were asked because such accidents are a common risk factor for pain in older workers . chronic diseases can also lead to work disability in the older population ; among our respondents , chronic diseases clinically diagnosed within 6 years of the beginning of klosa included hypertension , diabetes , bronchiolitis , emphysema , liver diseases ( excluding fatty liver ) , myocardial infarction , angina , heart failure , depression , anxiety , insomnia , excessive stress , senile psychosis , and others . according to the status of woles , the frequency and mean with standard deviation were calculated for each data category , and the chi - squared test was used to evaluate the association between categories . multiple logistic regression models were then used to calculate odds ratios ( ors ) and 95% confidence intervals ( 95% cis ) for the lower - woles group in relation to the number of sites where participants experienced pain and total pain severity . the multiple logistic models were adjusted for age , sex , household income , marriage status , residence , occupational classification , type of employment , working status , job satisfaction level , health behavioral factors such as smoking , drinking , and physical activity , chronic diseases ( hypertension , diabetes , chronic lung disease , liver disease , and cardiovascular disease ) , and history of traffic accidents . statistical analyses were performed with sas ( version 9.4 , sas institute , cary , nc , usa ) . a p value < 0.05 was considered to indicate statistical significance in both tails . there were 1,979 respondents in our sample , of which 1,175 ( 59.4% ) were male and 804 ( 40.6% ) were female . participants who were younger , had higher household income levels , had higher education levels , and were living with a spouse were somewhat more likely to have high woles . in terms of occupational characteristics , most of the participants were categorized as blue collar workers ( n=812 , 41.0% ) or self - employed workers ( n=954 , 48.2% ) , and 66.4% of people were satisfied with their jobs . according to pain sites , 32.3% of participants were suffering from lower extremes pain , and had a low mean woles ( 61.7 ) . the mean woles decreased according to an increased number of pain sites ( from 70.7 in none to 59.8 in more than three ) and severity ( from 70.7 in none to 62.2 in severe ) . demographic characteristics of the study participants and working life expectancy scale table 2 shows the characteristics of subjects according to woles status . most participants ( n=1,719 , 86.9% ) were categorized into the higher - woles group , whereas 260 were categorized into the lower - woles group . the proportion of women in the lower - woles group was observed to be higher ( 46.9% ) than that in the higher - woles group ( 39.7% ) , and this was statistically significant . in terms of age , most of the participants were aged 55 - 64 ( 54.6% of lower- and 75.6% of higher - woles group ) . there were differences in the household income level , educational status , and marital status of the people according to the woles groups . the highest proportion of employment type in the lower - woles group were paid workers ( 53.1% ) , and in the higher - woles group , self - employed ( 49.9% ) ( p=0.0006 ) . both the total number of pain sites and severity were found to have statistically significant differences according to the woles groups . regarding the number of pain sites , among subjects by the woles group ( lower / higher ) , 33.4/52.6% had no pain , 21.9/19.0% had pain at one site , 18.5/14.0% had pain at two sites , and 26.2/14.4% had pain at three or more sites ( p<0.001 ) . regarding total pain severity , among subjects by the woles group ( lower / higher ) 33.5/52.6% had no pain , 17.3/15.4% had mild pain , 13.1/9.9% had moderate pain , and 36.2/22.1% had severe pain ( p<.0001 ) . characteristics of study participants according to working life expectancy status the multiple logistic regression models were used to calculate or and 95% ci for the lower - woles group according to the nature of pain ( table 3 ) . as the number of sites with pain and severity of pain increased , the possibility of being included in the lower - woles group increased ( p for trend < 0.001 in both ) . after adjustment for all covariates , ors and 95% cis of the lower - woles group in relation to the number of pain sites were as follows : no site , reference ; 1 site , 1.75 ( 1.20 - 2.55 ) ; 2 sites , 1.99 ( 1.32 - 3.02 ) ; and 3 sites , 2.28 ( 1.51 - 3.41 ) . with respect to the total pain severity , ors and 95% cis of the lower - woles group versus the reference group with no pain were as follows : mild pain , 1.74 ( 1.16 - 2.61 ) ; moderate pain , 2.02 ( 1.28 - 3.22 ) ; and severe pain , 2.12 ( 1.46 - 3.08 ) . results of the odds ratio and 95% confidence intervals compare with expectation for working life expectancy according to pain characteristics using multiple logistic regression models . to the best of our knowledge , this is the first research to investigate the relationship between pain and woles in older workers . in this study , respondents reporting pain were more likely to be pessimistic regarding woles , a trend that increased with the number of pain sites and pain severity . furthermore , potential confounding factors such as the presence of chronic diseases did not attenuate this result , showing that pain affects woles independently of chronic diseases and other risk factors . however , our study shows that workers who suffer from pain might give up hope of continuing to work . hence , we consider worker pain an important social issue with regard to sustainable working life in aging workers . work ability and performance generally decrease with age , but workers with pain are less likely to participate in the labor force and have reduced work ability and performance compared with those without pain . older workers , even those with pain , may not consider leaving the workplace until their performance falls below their own standards ; indeed , they are often eager to continue work until they can no longer meet job demands . however , pain may cause a decline in task ability to a point at which the worker can no longer perform effectively . various studies have reported pain to be associated with psychological disorders such as cognitive impairment , anxiety , and depression , often as a cause or effect . some studies have suggested possible mechanisms for this relationship , highlighting the important role of neurobiological interactions . pain shares a pathway in the central nervous system with both cognition and mood ; that is , peripheral nociception and noxious stimuli activate the same pathway involved in depression and cognitive impairment . indeed , both serotonin and norepinephrine act as key mediators for pain as well as cognition , anxiety , and depression . the hypothalamic - pituitary - adrenal axis , which regulates the stress response , has also been suggested as a possible link between mental illness and physical stressors such as pain . it is well known that cognitive function declines with age , and this cognitive impairment is significantly associated with reduced workplace performance and safety . anxiety and depression indeed , the contribution of mental health status to prolong the working life among older workers should be substantial . the determinants of work ability could be impacted by self - rated job performance and workplace safety . thus , pain may aggravate mental as well as physical problems in older workers , further impairing their work performance and placing them at greater risk of an accident . these impacts were shown in our results as worked with decreased woles had higher pain natures . it is somewhat surprising that no attenuation of the association between pain and reduced expectation for sustainable working life was found after adjusting for chronic disease . as previously mentioned , chronic diseases can shorten working life , and numerous studies have emphasized the importance of chronic disease management in older workers with regard not only to individual health but also to reducing socio - economic burdens . we absolutely agree that chronic disease management is important , but the present study suggests that pain may shorten working life independently of chronic disease , making understanding and management of pain a potential major target in efforts to extend working life . this was the first attempt to investigate the relationship between pain and wole in aging workers . the work sustainability is a multidimensional condition and thus hard to assess among workers . nevertheless , an individual 's specific work demands , health conditions , and mental status linked to the perception of workers are important factors for work sustainability . a previous study indicated self - rated work ability is useful for investigation as well as in clinical practice to assess work sustainability . for example , even a single and simple one question survey about self - rated work ability could be used as a strong predictor for workers ' sick leave . we hoped to demonstrate the concept role of elders ' perception of woles like self - rated work ability . it can therefore be assumed that the self - rated woles were linked to workers ' health status or working conditions among the aging working population . a further study with more focus on self - rated woles is therefore suggested . the strength of this study is that it controlled for numerous possible covariates using data from a well - established survey of a nationally representative population . first , its cross - sectional design prevents the establishment of causal relationships between pain and reduced wole in older workers . second , our study relied on self - report questionnaires rather than medical examination for its data on pain and chances of wole . the lack of objective clinical measurements of pain might have resulted in inaccurate assessment of the relationship between pain and wole . also , pain tolerance differed by age , gender , race , or social circumstance . however , wole might be affected differently when pain is of unknown origin or nature . furthermore , self - reporting of the sites and severity of pain is considered an effective method in the field of pain medicine . as for wole , we did not investigate it in an occupational medicine setting , but merely through answers to a simple question . however , there is no consensus on the appropriate method for measuring wole , and previous studies indicate that self - perceived working ability and willingness to work , as measured by us , are important in extending working life . third , a note of caution is due here since the number of study participants might be too small for an overall survey sample size . these results therefore need to be interpreted and applied to general aging working population with caution . our large cross - sectional study including an older working population showed the relationship between pain ( both total pain sites and severity ) and wole . this association was not attenuated even after adjustment for age , sex , population of area of residence , household income , education , marriage status , alcohol consumption , smoking behavior , physical activity level , chronic disease ( hypertension , diabetes , lung disease , cardiovascular disease , and psychological disorders ) , and history of traffic accidents . our results suggest that pain management should be considered a key factor in extending sustainable working life in aging workers , particularly for those with pain at multiple sites or severe pain . conflicts of interest : the authors declare no conflicts of interest . 
 acknowledgments : the authors would like to thank the participants of klosa for the opportunity for performing this research .
objectives : many aging workers wish to continue working as long as they can for a better life in the future . however , symptoms of pain are a key obstacle in the continuation of work among older workers . 
 the impact of pain on work is understudied . 
 thus , we investigated the relationship between pain characteristics ( total site and severity ) and aging workers ' working life expectancy scale ( woles ) in korea.methods : we included 1,979 participants ( 1,175 men and 804 women ) from a well - established survey of a nationally representative population : the korean longitudinal study of ageing . 
 a self - questionnaire was used to assess pain characteristics and woles . 
 odds ratios ( ors ) and 95% confidence intervals ( cis ) for the lower - woles group were calculated using multiple logistic regression models . 
 results : compared with the absence of pain , ors and 95% cis of the lower - woles group were increased , as follows : 1 pain site , 1.75 ( 1.20 - 2.55 ) ; 2 pain sites , 1.99 ( 1.32 - 3.03 ) ; 3 or more pain sites , 2.28 ( 1.51 - 3.42 ) ; mild pain , 1.74 ( 1.32 - 2.61 ) ; moderate pain , 2.02 ( 1.28 - 3.22 ) ; and severe pain , 2.12 ( 1.46 - 3.08 ) . 
 the statistical trend was significant in both total sites and severity of pain ( p<0.001 ) . 
 conclusions : there was a significant association between woles and both total pain sites and severity of pain , even after adjusting for potential confounding factors .