benign prostatic hyperplasia ( bph ) is one of the most frequently occurring urologic diseases in men older than 50 . the bladder outlet obstruction causes a variety of urinary symptoms including nocturia , incomplete voiding , urgency , and hesitancy and comes to the fore as a significant health problem interrupting the quality of life of men over middle age . the prevalence rate of bph increases with age ; bph occurs in 40% to 70% of men aged 60 to 70 years . the current korean population is aging very rapidly compared with other countries ; with this , interest in health after middle age is increasing throughout society . however , owing to a lack of recognition about bph , the time until visiting the hospital is often delayed , and this tendency is truer in rural areas than in urban areas . in this situation , it is necessary to understand the prevalence rate of bph , but few systematic epidemiologic investigations have been carried out about bph in korea . also , there are limitations in the epidemiologic research conducted so far because the previous data were not collected by use of standardized diagnostic criteria or a specific clinical definition . therefore , in this study , the prevalence rate of bph was estimated among males living in the rural korean area of yangpyeong country . this study was conducted to investigate the prevalence rate of bph and its related factors on the basis of an epidemiologic investigation among males in one rural community in korea . the department of preventive medicine and the department of urology in hanyang university guri hospital planned the cohort research by targeting yangpyeong county . the participants of this study were males aged 40 and above in yangpyeong county , gyeonggi - do . the participants were recruited over august to september 2009 , august 2010 , and august 2011 . trained investigators collected the international prostate symptom score ( ipss ) , individual medical history , and demographic information for each participant . we excluded those already diagnosed with bph who were receiving treatment and taking health food supplements . prostate disease was assessed by measuring serum prostate - specific antigen ( psa ) , a doctor 's medical examination by interview , a digital rectal examination , and prostate volume by transrectal ultrasound ( sa6000ii , medison inc . , seoul , korea ) . a total of 799 males responded to all of the survey questions and underwent examinations . among them , 668 subjects remained for study after the exclusion of 1 person who did not consent to participate in the study , 1 person who had a prostate cancer history , and 109 subjects who were missing the digital rectal examination , transrectal ultrasonography , or other epidemiologic inf ormation . among these subjects , data were analyzed from the 599 subjects finally participating in this study after the exclusion of subjects in whom a nodule was perceived or who had a serum psa score of 4.0 or higher and thus who might have prostate cancer ( fig . 1 ) the severity of luts was evaluated by the ipss and quality of life and the participants were divided into four groups by age ( 40 - 49 , 50 - 59 , 60 - 69 , and 70 years and above ) . this study was approved by the institutional review board ( irb ) of hanyang university college of medicine . the irb numbers were hyuh irb 2010-r-38 and 2011 - 07 - 005 . in this study , bph was defined as a score of 8 or higher on the ipss and a prostate volume of 25 ml or above by transrectal ultrasonography , according to the criteria of the fourth edition of the textbook of urology published by the korean urological association . the prevalence rate of bph was compared by classifying the groups by age : 40 - 49 , 50 - 59 , 60 - 69 , and 70 years and above . in addition , the prevalence rate of each luts was checked by classifying the total ipss in each group into a mild symptom group ( score of 1 - 7 ) , a moderate symptom group ( score of 8 - 19 ) , and a severe symptom group ( score of 20 - 35 ) . additionally , the analysis was conducted on the correlations between the epidemiologic factors ( age , marital status , education level , smoking status , alcohol consumption status , regular exercise , body mass index [ bmi ] ) , comorbidities ( hypertension , diabetes ) , and serum psa and bph . , cary , nc , usa ) was used for the statistical analysis ; we also used the chisquare test , independent t - test , analysis of variance , and logistic regression analysis . the results of the statistical analysis were considered to be significant when the p - value was less than 0.05 . this study was conducted to investigate the prevalence rate of bph and its related factors on the basis of an epidemiologic investigation among males in one rural community in korea . the department of preventive medicine and the department of urology in hanyang university guri hospital planned the cohort research by targeting yangpyeong county . the participants of this study were males aged 40 and above in yangpyeong county , gyeonggi - do . the participants were recruited over august to september 2009 , august 2010 , and august 2011 . trained investigators collected the international prostate symptom score ( ipss ) , individual medical history , and demographic information for each participant . we excluded those already diagnosed with bph who were receiving treatment and taking health food supplements . prostate disease was assessed by measuring serum prostate - specific antigen ( psa ) , a doctor 's medical examination by interview , a digital rectal examination , and prostate volume by transrectal ultrasound ( sa6000ii , medison inc . , seoul , korea ) . a total of 799 males responded to all of the survey questions and underwent examinations . among them , 668 subjects remained for study after the exclusion of 1 person who did not consent to participate in the study , 1 person who had a prostate cancer history , and 109 subjects who were missing the digital rectal examination , transrectal ultrasonography , or other epidemiologic inf ormation . among these subjects , data were analyzed from the 599 subjects finally participating in this study after the exclusion of subjects in whom a nodule was perceived or who had a serum psa score of 4.0 or higher and thus who might have prostate cancer ( fig . 1 ) the severity of luts was evaluated by the ipss and quality of life and the participants were divided into four groups by age ( 40 - 49 , 50 - 59 , 60 - 69 , and 70 years and above ) . this study was approved by the institutional review board ( irb ) of hanyang university college of medicine . in this study , bph was defined as a score of 8 or higher on the ipss and a prostate volume of 25 ml or above by transrectal ultrasonography , according to the criteria of the fourth edition of the textbook of urology published by the korean urological association . the prevalence rate of bph was compared by classifying the groups by age : 40 - 49 , 50 - 59 , 60 - 69 , and 70 years and above . in addition , the prevalence rate of each luts was checked by classifying the total ipss in each group into a mild symptom group ( score of 1 - 7 ) , a moderate symptom group ( score of 8 - 19 ) , and a severe symptom group ( score of 20 - 35 ) . additionally , the analysis was conducted on the correlations between the epidemiologic factors ( age , marital status , education level , smoking status , alcohol consumption status , regular exercise , body mass index [ bmi ] ) , comorbidities ( hypertension , diabetes ) , and serum psa and bph . , cary , nc , usa ) was used for the statistical analysis ; we also used the chisquare test , independent t - test , analysis of variance , and logistic regression analysis . the results of the statistical analysis were considered to be significant when the p - value was less than 0.05 . there were 45 subjects ( 7.5% ) in the aged 40 - 49 years group , 165 subjects ( 27.5% ) in the aged 50 - 59 years group , 200 subjects ( 33.4% ) in the aged 60 - 69 years group , and 189 subjects ( 31.5% ) in the aged 70 years and above group . the prostate volume of the entire group of participants was 30.2510.14 g , and the average psa level was 1.200.79 ng / ml . the ipss and the quality of life score were 5.966.72 and 2.701.04 , respectively . in the age groups , the ipss was 2.223.76 in men aged 40 - 49 years , 3.505.06 in those aged 50 - 59 , 6.756.94 in those aged 60 - 69 , and 8.167.28 in men aged 70 or more . these changes with age were statistically significant ( p<0.001 ) . also , prostate volume was 25.365.22 g in men aged 40 - 49 years , 30.299.12 g in men aged 50 - 59 years , 30.549.7 g in men aged 60 - 69 years , and 31.0711.91 g in men aged 70 years and above , and these age - related increases were statistically significant ( p=0.008 ) . a total of 120 subjects ( 20.0% ) in the entire group of participants met the standard of bph as defined in this study . when we examined the prevalence rate according to age , we found that the prevalence rate increased with age . there were 2 subjects ( 4.4% ) with bph in the and aged 40 - 49 years group , 18 subjects ( 10.9% ) in the aged 50 - 59 years group , 44 subjects ( 22% ) in the aged 60 - 69 years group , and 56 subjects ( 26.6% ) in the aged 70 years and above group , and this increase with age was statistically significant ( p<0.001 ) ( table 1 ) . a total of 120 participants ( 20% ) met the definition of bph in this study . the average age of the bph group was 68.238.52 years , the average ipss was 14.675.95 , the average prostate volume was 37.0411.71 g , and the average psa level was 1.560.88 ng / ml ( table 2 ) . in the subscores of the ipss , the score for weak urinary stream was highest ( 3.372.08 ) ; the scores for incomplete emptying ( 2.432.18 ) , hesitancy ( 2.192.15 ) , and nocturia ( 2.051.31 ) were also high . in the survey questions about quality of life , the overall inconvenience of the patients due to their current urinary symptoms was used for the score ; the scores were divided from 0 as very satisfied to 6 as very dissatisfied . the quality of life score was significantly higher in the bph group ( 3.480.93 ) than in the non - bph group ( 2.500.91 ) . in this study , we conducted a correlation analysis to determine whether epidemiologic factors ( marital status , education level , smoking status , alcohol consumption status , bmi , and regular exercise ) and comorbidities ( hypertension and diabetes ) influenced the risk of bph . the non - bph group had a higher proportion of smokers than did the bph group ( table 3 ) . the reason the epidemiologic factors including lifestyle did not show a significant correlation may be that this study was based on a cross - sectional design that did not clearly show a sequential relationship by time . in the case of the bph group , the patients ' uncomfortable urinary status could have already influenced changes in health behavior . there were 45 subjects ( 7.5% ) in the aged 40 - 49 years group , 165 subjects ( 27.5% ) in the aged 50 - 59 years group , 200 subjects ( 33.4% ) in the aged 60 - 69 years group , and 189 subjects ( 31.5% ) in the aged 70 years and above group . the prostate volume of the entire group of participants was 30.2510.14 g , and the average psa level was 1.200.79 ng / ml . the ipss and the quality of life score were 5.966.72 and 2.701.04 , respectively . in the age groups , the ipss was 2.223.76 in men aged 40 - 49 years , 3.505.06 in those aged 50 - 59 , 6.756.94 in those aged 60 - 69 , and 8.167.28 in men aged 70 or more . these changes with age were statistically significant ( p<0.001 ) . also , prostate volume was 25.365.22 g in men aged 40 - 49 years , 30.299.12 g in men aged 50 - 59 years , 30.549.7 g in men aged 60 - 69 years , and 31.0711.91 g in men aged 70 years and above , and these age - related increases were statistically significant ( p=0.008 ) . a total of 120 subjects ( 20.0% ) in the entire group of participants met the standard of bph as defined in this study . when we examined the prevalence rate according to age , we found that the prevalence rate increased with age . there were 2 subjects ( 4.4% ) with bph in the and aged 40 - 49 years group , 18 subjects ( 10.9% ) in the aged 50 - 59 years group , 44 subjects ( 22% ) in the aged 60 - 69 years group , and 56 subjects ( 26.6% ) in the aged 70 years and above group , and this increase with age was statistically significant ( p<0.001 ) ( table 1 ) . a total of 120 participants ( 20% ) met the definition of bph in this study . the average age of the bph group was 68.238.52 years , the average ipss was 14.675.95 , the average prostate volume was 37.0411.71 g , and the average psa level was 1.560.88 ng / ml ( table 2 ) . in the subscores of the ipss , the score for weak urinary stream was highest ( 3.372.08 ) ; the scores for incomplete emptying ( 2.432.18 ) , hesitancy ( 2.192.15 ) , and nocturia ( 2.051.31 ) were also high . in the survey questions about quality of life , the overall inconvenience of the patients due to their current urinary symptoms was used for the score ; the scores were divided from 0 as very satisfied to 6 as very dissatisfied . the quality of life score was significantly higher in the bph group ( 3.480.93 ) than in the non - bph group ( 2.500.91 ) . in this study , we conducted a correlation analysis to determine whether epidemiologic factors ( marital status , education level , smoking status , alcohol consumption status , bmi , and regular exercise ) and comorbidities ( hypertension and diabetes ) influenced the risk of bph . the non - bph group had a higher proportion of smokers than did the bph group ( table 3 ) . the reason the epidemiologic factors including lifestyle did not show a significant correlation may be that this study was based on a cross - sectional design that did not clearly show a sequential relationship by time . in the case of the bph group , bph generally occurs in males in their 50s ; 80% of males in their 70s suffer from the luts related to bph . because in current korean society the population is aging , the older population is rapidly increasing . additionally , the incidence of metabolic syndrome , which is a risk factor for bph , and the number of patients with obesity are also annually increasing owing to westernized eating habits . bph and luts could lead to social problems caused by the increase in annual medical expenses related to serious complications such as falls , depression , and reduced quality of life , particularly in the elderly . in this situation , it is necessary to conduct systematic epidemiologic investigations of the prevalence rate of bph in korea . to investigate the prevalence rate of bph , it is f irst necessary to clarify the diagnostic criteria of bph . although methods exists for the diagnosis of bph , including taking the patient 's medical history and recording urinary symptoms , prostate volume measurement by digital rectal examination and transrectal ultrasonography , peak urinary flow rate ( qmax ) , and residual urine measurement , accurate diagnostic criteria have not been established . currently , bph is mainly defined clinically on the basis of the ipss , prostate volume , and qmax . garraway et al .   defined bph as urinary symptoms , prostate volume of 20 ml or more as measured by transrectal ultrasonography , and qmax of 15 ml / s or less . in their study , they reported that the prevalence rate of bph was 14% in males in their 40s and 40% in males in their 70s . bosch et al .   defined bph as a prostate volume of 30 ml or more and ipss of 8 points or higher and reported a bph prevalence rate of 19% . in a study targeting males aged 40 years and older in spain . in studies defining bph in korea , rhew et al . defined bph as an ipss of 8 points or higher and a qmax of 10 ml / s or less . defined it as an ipss of 8 points or higher , prostate volume by digital rectal examination of 30 ml or more , and qmax of 15 ml / s or less . in studies investigating the prevalence rate in seongnam city and jeju island , bph was defined as an ipss of 8 points or higher and prostate volume measured by transrectal ultrasonography of 30 ml or more . in this study , bph diagnosis was based on the symptom score and the prostate volume , and urof lowmetry examination was excluded . reported that the bph prevalence rate defined by two variables including symptom score and prostate volume and the bph prevalence rate defined by three variables including symptom score , prostate volume , and qmax were 12% and 10% , respectively , and that there was no statistically significant difference between the two rates . second , it was thought that there could be many errors when determining bph based on 10 ml / s or less or 15 ml / s or less in epidemiologic examinations because uroflowmetry can vary depending on the amount of urination . measured prostate volume through transrectal ultrasonography by targeting 175 males whose ages were between 27 and 70 years ; the average prostate volume of adenoma prostate was significantly higher than that of nonadenoma prostate : 28.0 ml ( range , 14.5 - 62.1 ml ) vs. 23.0 ml ( range , 11.3 - 39.1 ml ) . therefore , those authors proposed criteria for bph as an ipss of 8 points or higher and a prostate volume by transrectal ultrasonography of 25 ml or more . the bph prevalence rate was 20% ( 120/599 subjects ) in the present study and lower than the rate in other reports in korea . the reason for this could be that 210 of 599 males ( 35% ) were in their 40s to 50s and were thus relatively younger than the groups in the other studies in korea . bph prevalence rates reported in korea were 40% in the urban area of seongnam and 25.5% in busan . in addition , the prevalence rates were 23.2% in the rural area of yeoncheon , gyeonggi - do , and 27.7% in the inland area of chungcheongbuk - do . first , there were variables in the epidemiologic investigation , such as the selection of the target group and regional differences in the population . the prevalence rate in seongnam was much higher than in other regions because the study was an epidemiologic investigation targeting the elderly population ( 65 years old and above ) . although lee et al .   conducted an epidemiologic investigation for the first time in yeoncheon area in 1995 , they only conducted a survey of the ipss and then estimated the prevalence rate of bph . reported that the bph prevalence rate as assessed by luts , digital rectal examination , and uroflowmetry examination was 11% ; here , the question about the accuracy of measuring prostate size could be raised because the prostate volume was measured by digital rectal examination . in this study , the survey and the epidemiologic investigation were performed by interviewers who were sufficiently trained ; unlike other authors ' measurement of the prostate volume by digital rectal examination , it could be thought that the reliability would be high because the prostate volume was accurately measured by transrectal ultrasonography . epidemiologic research on bph has greatly evolved over the past several years , and many epidemiologic data have been accumulated . even though age and genetics play an important role as causes of bph , it is notable that lifestyle factors such as metabolic syndrome or cardiovascular disease , which can be corrected , have a considerable impact on the natural progression of bph . one cohort study showed that luts prevalence increased by 80% in the group diagnosed with at least three components of the metabolic syndrome compared with the group without diagnosed components of the metabolic syndrome . additionally , other studies have shown that the risk of bph and luts is significantly increased in people with heart disease . in other previous studies , a correlation was observed in which the more the amount of fat increased , the more the prostate volume increased . in several research studies , weight , bmi , and waistline all showed a significant correlation with prostate volume . in this study , there was no significant difference in bmi between the bph group and the non - bph group . the reason for this may be that the cross - sectional design of this study did not clearly show the sequential relationship of time . the study criteria were also vague because there are few studies related to bmi and prostate volume in asia , including korea . in the longitudinal study of aging cohort in baltimore , maryland ( usa ) , each 1-kg / m increase in bmi corresponded to a 0.41-ml prostate volume increase . compared with nonobese participants ( bmi<25 kg / m ) , the obese participants ( bmi35 kg / m ) showed a 3.5-time higher bph risk . in addition , whereas some studies reported that there was a reverse protective effect of smoking on bph and luts , other studies reported that the risk level increased or showed no change . therefore , it is necessary to conduct more studies on the correlation between smoking and bph . first , the subjects were not a random sample of the population because we recruited subjects through a prostate health screening campaign . second , we did not consider the difference in the population distribution by age in yangpyeong county and the study group . third , although prevalence was the number of cases of the condition at a particular point in time , the participants of this study were recruited over 3 years ( august - september 2009 , august 2010 , and august 2011 ) in an effort to collect more participants . consequently , the results of this epidemiologic research investigating the bph prevalence rate in a rural korean area showed a lower value than in other countries . one reason for this may be that the ratio of relatively younger males in their 40s to 50s was somewhat higher in this epidemiologic investigation than in other studies . second , there may have been an influence of diet , with a focus on vegetables in the rural area compared with the westernized diet of high meat consumption in urban areas . although our study did not survey the eating habits of the individuals , in a study performed to evaluate food intake of the elderly residing in different regions of korea , the intake of meats was significantly higher in urban elderly than in rural elderly . third , the different diagnostic criteria of bph applied in each study could be a cause of the differences in prevalence rates . in this study , the prevalence rate of bph was estimated by targeting males aged 40 years and older in a rural korean area . the results showed that the prevalence rate of bph in males aged 40 years and older in yangpyeong county was 20.0% . when classifying the men according to age , none of the epidemiologic factors studied including lifestyle showed a statistically significant correlation with bph , except for smoking . this study showed a lower prevalence rate of bph in a rural area than reported in other studies in korea . unlike other studies conducted in rural areas , however , the reliability of this study can be considered to be high because prostate volume was measured by use of a more objective method .