hypertension presents a significant public health burden due to increased cardiovascular disease , mortality , disability , and economic cost . it is becoming an increasingly common health problem worldwide because of increasing longevity and a higher prevalence of contributing factors , such as obesity , physical inactivity and an unhealthy diet . worldwide hypertension is estimated to cause 7.1 million premature deaths and 4.5% of the disease burden . mortality rate per 100,000 persons due to high blood pressure varies from country to country . it is reported that the mortality rate due to hypertension was 15.9 per 100,000 persons in the united states in 2000 and 4.5 in 2002 in japan . the mortality rate due to high blood pressure in korea increased slightly , from 10.6 to 11.0 per 100,000 persons , between 2002 and 2007 . currently , the prevalences of hypertension in many developing countries , particularly in urban areas , are as high as those seen in developed countries [ 5 - 8 ] . in contrast to previous studies in other developing countries , the prevalence of hypertension in korean adults (  30 yrs ) decreased from 30% to 24.9% between 1998 and 2007   and the trends of regional differences in prevalence of hypertension were observed in opposite direction ; the prevalence of hypertension were 26.2% in metropolitan areas while 34.3% in small towns . indeed , hypertension rate in chungcheong province , which is not in metropolitan area , increased from 22.1% in 2001 to 28.0% in 2005 , while normotensive rate decreased from 47.7% in 2001 to 41.0% in 2005 . local traditional and seasonal variations in foods intake are common in korea , due to environmental differences such as regional variations in climate and geographical characteristics . the prevalence of hypertension in rural areas may differ from metropolitan areas based on these variations . based on the korean health and nutrition examination survey ( knhanes ) iii report , healthy lifestyles , including healthy diet patterns , were observed more in urban areas than in rural areas . sodium intake was relatively higher in rural areas than in urban areas ( 4,834 mg vs. 4,571 mg ) . community nutritionists should consider these regional variations and characteristics when they plan hypertension management program for the community residents . the target of this research area , chungcheong province , is located in central area of south korea , and includes the inland area , chungcheongbuk - do and the west coast border , chungcheongnam - do . the characteristics of local food culture in chungcheong province is a mix between that of the inland and the west coast area . particularly , people in this province have traditionally used a wide variety of salted foods , including abundant sea foods , which leads to high sodium intake and might eventually relate to high blood pressure and a risk of hypertension . therefore , this study was executed to reveal the relationship of blood pressure to intakes of sodium , potassium , and calcium and to the sodium / calcium ratio and the sodium / potassium ratio in residents of chungcheong province using knhanes iii data . it is hoped that this study can contribute to the creation of a guideline for the prevention and treatment of hypertension attuned to regional differences . the data analyzed in the present study were obtained from knhanes iii , conducted by the ministry for health , welfare and family affairs in korea . knhanes has been conducted every three years since 1998 , and the raw data are released to the public for scientific use . knhanes consists of a health interview survey , a health behavior survey , a health examination survey , and a nutrition survey . the surveys are given to stratified multistage samples of the south korean population from multiple geographic areas , ages , and sexes . trained interviewers administered structured questionnaires in participants ' homes to obtain information on sociodemographic characteristics , lifestyle , health , nutritional status , and the use of dietary supplements . in total , 33,848 people responded to knhanes iii , but only 7,597 people participated in the health behavior survey , the health examination survey , and the nutrition survey . from this group , 544 adults aged 19 years or older in chungcheong province were selected for the present study . data from the health examination survey were used to obtain information on smoking , alcohol intake , and physical activity . intakes of energy , sodium , potassium , and calcium were obtained from the nutrition survey , while data on height , weight , body mass index ( bmi ) , blood pressure [ systolic blood pressure ( sbp ) and diastolic blood pressure ( dbp ) ] , and pulse rate were obtained from the health examination survey . hypertension was identified in individuals who met at least 1 of 4 criteria from the knhanes iii data : self - reports of physician diagnosis of hypertension ; self - reports of antihypertensive drug intake ; sbp  140 mmhg ; dbp  90 mmhg . blood pressure measurements were taken three times in a stable state , and the average sbp and dbp measurements were used to determine hypertension . as part of the standard knhanes data collection protocol , 24-hour dietary recalls were elicited , and here were used to estimate intakes of energy , sodium , potassium , and calcium . general characteristics , nutrient intakes , and anthropometric data were compared across the normotensive and hypertensive group . in addition , sodium , potassium , and calcium intakes were calculated per 1,000 kcal of energy . income groups were categorized according to average monthly income in 2005 in relation to the minimum cost of living . low income was defined as an average monthly income that was , at most , 1.2 times the minimum cost of living ; middle income was defined as an average monthly income that was 1.2 to 2.5 times the minimum cost of living ; and high income was defined as an average monthly income that was more than 2.5 times the minimum cost of living . subjects were also categorized based on their educational level , defined as middle school or less ( 9 years and below ) , high school ( 10 - 12 years ) , and college or more ( 13 years or more ) . present smoking status was used to classify each subject as a " current smoker " , " ex - smoker " , or " non - smoker " . metabolic equivalent of task values ( mets ) were used to classify physical activity as low , middle , or high . mets are multiples of the resting metabolic rates and were calculated using the short form ( version 2.0 , april 2004 ) of the international physical activity questionnaire ; that is , low activity was 600 > met - minutes / week , middle activity was 600  met - minutes / week < 3,000 , and high activity was 3,000  met - minutes / week . responses for the question regarding following the instructions of eating a healthy diet ( reducing salt consumption ) were classified as " take action " , " try to practice " , and " do not practice " . all analyses used survey weighting to account for the complex survey design that consisted of multistage , stratified , and clustered sampling . probability sampling weights were used with strata and primary sampling units in the data analysis . subject characteristics were compared between the normotensive and the hypertensive groups using a chi - square test . mean values and standard errors for nutrient intakes were calculated and t - test was used to verify significance for each normotensive and hypertensive group . to determine the impact of risk factors on high blood pressure , weight , waist circumference , sodium , potassium , and calcium intake were each classified by tertile . we estimated odds ratios ( ors ) using multiple logistic regression , adjusted for age ( 19 - 29 , 30 - 49 , 50 - 64 ,  65 ) , sex , education ( middle school or lower , high school , college or higher ) , bmi , alcohol drinking ( drinker , non - drinker ) , and energy intake . all statistical analyses were performed using survey procedure of sas software ( version 9.12 , cary , nc , usa ) and descript procedure of suddan software ( release 9.0 , research triangle institute , research triangle park , nc , usa ) applying a significance level of p < 0.05 . the data analyzed in the present study were obtained from knhanes iii , conducted by the ministry for health , welfare and family affairs in korea . knhanes has been conducted every three years since 1998 , and the raw data are released to the public for scientific use . knhanes consists of a health interview survey , a health behavior survey , a health examination survey , and a nutrition survey . the surveys are given to stratified multistage samples of the south korean population from multiple geographic areas , ages , and sexes . trained interviewers administered structured questionnaires in participants ' homes to obtain information on sociodemographic characteristics , lifestyle , health , nutritional status , and the use of dietary supplements . in total , 33,848 people responded to knhanes iii , but only 7,597 people participated in the health behavior survey , the health examination survey , and the nutrition survey . from this group , 544 adults aged 19 years or older in chungcheong province were selected for the present study . data from the health examination survey were used to obtain information on smoking , alcohol intake , and physical activity . intakes of energy , sodium , potassium , and calcium were obtained from the nutrition survey , while data on height , weight , body mass index ( bmi ) , blood pressure [ systolic blood pressure ( sbp ) and diastolic blood pressure ( dbp ) ] , and pulse rate were obtained from the health examination survey . hypertension was identified in individuals who met at least 1 of 4 criteria from the knhanes iii data : self - reports of physician diagnosis of hypertension ; self - reports of antihypertensive drug intake ; sbp  140 mmhg ; dbp  90 mmhg . blood pressure measurements were taken three times in a stable state , and the average sbp and dbp measurements were used to determine hypertension . as part of the standard knhanes data collection protocol , 24-hour dietary recalls were elicited , and here were used to estimate intakes of energy , sodium , potassium , and calcium . general characteristics , nutrient intakes , and anthropometric data were compared across the normotensive and hypertensive group . in addition , sodium , potassium , and calcium intakes were calculated per 1,000 kcal of energy . income groups were categorized according to average monthly income in 2005 in relation to the minimum cost of living . low income was defined as an average monthly income that was , at most , 1.2 times the minimum cost of living ; middle income was defined as an average monthly income that was 1.2 to 2.5 times the minimum cost of living ; and high income was defined as an average monthly income that was more than 2.5 times the minimum cost of living . subjects were also categorized based on their educational level , defined as middle school or less ( 9 years and below ) , high school ( 10 - 12 years ) , and college or more ( 13 years or more ) . present smoking status was used to classify each subject as a " current smoker " , " ex - smoker " , or " non - smoker " . metabolic equivalent of task values ( mets ) were used to classify physical activity as low , middle , or high . mets are multiples of the resting metabolic rates and were calculated using the short form ( version 2.0 , april 2004 ) of the international physical activity questionnaire ; that is , low activity was 600 > met - minutes / week , middle activity was 600  met - minutes / week < 3,000 , and high activity was 3,000  met - minutes / week . responses for the question regarding following the instructions of eating a healthy diet ( reducing salt consumption ) were classified as " take action " , " try to practice " , and " do not practice " . all analyses used survey weighting to account for the complex survey design that consisted of multistage , stratified , and clustered sampling . probability sampling weights were used with strata and primary sampling units in the data analysis . subject characteristics were compared between the normotensive and the hypertensive groups using a chi - square test . mean values and standard errors for nutrient intakes were calculated and t - test was used to verify significance for each normotensive and hypertensive group . to determine the impact of risk factors on high blood pressure , weight , waist circumference , sodium , potassium , and calcium intake were each classified by tertile . we estimated odds ratios ( ors ) using multiple logistic regression , adjusted for age ( 19 - 29 , 30 - 49 , 50 - 64 ,  65 ) , sex , education ( middle school or lower , high school , college or higher ) , bmi , alcohol drinking ( drinker , non - drinker ) , and energy intake . all statistical analyses were performed using survey procedure of sas software ( version 9.12 , cary , nc , usa ) and descript procedure of suddan software ( release 9.0 , research triangle institute , research triangle park , nc , usa ) applying a significance level of p < 0.05 . general characteristics of the participants in the normotensive and the hypertensive group are shown in table 1 . one hundred and fifty two people were classified as hypertensive subjects ; the prevalence rate of hypertension was 23.0% . there was no sex difference between the normotensive and the hypertensive group : men made up 50.1% in the normotensive group , and 49.9% of the hypertensive group . there was also no difference between the normotensive and the hypertensive group according to income , smoking , and physical activity . persons aged 65 years or older and persons aged 50 - 64 years accounted for 37.6% and 36.5% , respectively , of the hypertensive subjects , significantly different from the percentages of normotensive subjects ( p < 0.001 ) . persons who had achieved an education level of middle school or lower accounted for 65.1% in the hypertensive group , while persons in the same education level were 24.2% of the normotensive group . alcohol drinkers accounted for 79.7% of the hypertensive group , which was significantly lower than in the normotensive group ( 88.0% , p = 0.042 ) . the bmi of the hypertensive group was significantly higher than that of the normotensive group . the mean bmi in the hypertensive group was 24.7 kg / m , significantly higher than that of the normotensive group ( p < 0.001 ) . the mean sbp of the normotensive group was 113.7 mmhg , whereas that of the hypertensive group was 139.5 mmhg . the mean dbp of the hypertensive group was 86.4 mmhg ( p < 0.001 ) . the mean pulse rate was 70.4 beats / min the hypertensive group , while that of normotensive group was 67.7 beats / min , without a significant difference ( table 1 ) . energy and nutrient intakes of the normotensive and hypertensive subjects in chungcheong province are shown in table 2 . no significant differences in energy and nutrient intake between the normotensive and hypertensive groups were observed . also , the sodium / potassium ratio and sodium / calcium ratio of the hypertensive group did not differ from that of the normotensive group . the results of logistic regression of hypertension prevalence among korean adults by sodium , potassium , and calcium intake are shown in table 3 . sodium intake did not show a relationship with the risk of hypertension , after adjusting for age , sex , education , bmi , alcohol drinking and energy intake . ( 2,197.1 - 3,153.6 mg ) reduced hypertension risk by 57% compared to t1 ( 0- < 2,197.1 mg ) . a reduced risk for hypertension was most pronounced in the t2 ( 380.5- < 572.6 mg / day , multivariate or = 0.43 , 95% ci : 0.21 - 0.88 ) and t3 tertiles of calcium (  572.6 mg / day , multivariate or = 0.43 , 95% ci : 0.20 - 0.90 ) with a significant trend in risk ( p for trend = 0.040 ) . persons with a sodium / calcium ratio of over 12.62 had a significantly increased risk of hypertension by 110% with a significant trend in risk ( multivariate or = 2.10 , 95% ci : 1.25 - 3.52 , p for trend = 0.002 ) . the response for following the instructions of eating a healthy diet was analyzed , and persons in the " do not practice " group had a 98% higher hypertension risk ( crude or = 1.98 , 95% ci : 1.08 - 3.62 ) than those of the " take action " group ( table 3 ) . however , multivariate ors of the response did not differ significantly among three types of responses . in the present study , we examined the effects of nutrients on blood pressure in the 19 year - old and older korean population , especially in chungcheong province using knhanes iii . there were significant differences in age , education level , alcohol drinking , and bmi between the normotensive and hypertensive group . nutrient intake between normotensive and hypertensive group did not differ but raised the risk of hypertension ; increased potassium and calcium intake reduced the risk of hypertension and increased sodium / calcium ratio raised 2.10 times more the risk of hypertension . several studies revealed that smoking was a factor that increased the risk of hypertension , whereas appropriate physical activities lowered blood pressure . physical activity accounted for 5 - 14% of the population attributable risk percentage ( par ) in western populations - finland , italy , the netherlands , uk , and usa [ 8,11 - 13 ] . however , there was no difference of smoking , and physical activities between the two groups in this study , which did not coincide with the figures in other studies . also , there was no difference of income levels between the two groups . in contrast , there was a significant difference between the two groups with regard to education levels , alcohol drinking , and bmi . this tendency was also observed in other studies ; persons with hypertension showed relatively lower education levels compared to the normotensive persons . it is well known that increased bmi raises the risk of hypertension [ 13 - 17 ] . this study also demonstrated that higher bmi was related to higher risk of hypertension significantly . overweight was an important risk factor , accounting for 11 - 25% par in the human population . logistic regression analysis was conducted in this study after grouping the tertiles of sodium , potassium and calcium intake , respectively . however , the results of the crude ors and multivariate ors did not differ significantly between sodium intake and risk of hypertension ( p for trend = 0.489 and 0.216 , respectively ) . high sodium intake accounted for 9 - 17% of par in western populations with national differences , and other epidemiological studies reported the association between sodium intake and hypertension . the risk of hypertension was significantly elevated with increasing sodium intake in guangxi bai ku yao and han populations in china ( or = 1.479 , p = 0.002 ) . reported that sodium intake increased dbp in the normotensive and non - medicated hypertensive subjects in a mediterranean population . a recent study of nhanes iii data also showed that subjects in the higher quartile of sodium intake were more likely to have a higher dbp . this difference from other studies may be the result of limitations of national level cross - sectional data , although the data was adjusted for confounding factors . the variation in sodium intake was more than double the variation in calcium or potassium intake . furthermore , high sodium intake level may partially contribute to the discrepancy between this and other studies ; the mean sodium intakes of both the hypertensive and the normotensive group in the present study was over 5,500 mg / day , which is 2.5 times higher than the recommended intake level for sodium . although sodium intake did not affect the risk of hypertension in the present study , salt intake was known to be related to sodium intake and associated with blood pressure . persons who responded as " do not practice " regarding following the instructions for eating a healthy diet had a 1.98 times ( crude ors , 95% ci : 1.08 - 3.62 ) higher risk of hypertension than those who were classified as " take action " . dietary management of hypertension may be more effective if the focus is on the overall nutritional profile and life style managements rather than single - nutrient intake as currently recommended for most patients . moderate potassium intakes ( t2 ) reduced the risk of hypertension by 57% ( or = 0.43 , 95% ci : 0.20 - 0.89 , p for trend = 0.088 ) , but there was no association between the sodium / potassium ratio and the risk of hypertension in this study . it is widely hypothesized that an appropriate potassium intake will lower hypertension risk . however , epidemiological evidence of the effect of potassium on blood pressure is inconsistent [ 12,16,23 - 25 ] . reported that low potassium intake substantially contributes to the prevalence of hypertension ; they suggested that in five western countries the par of hypertension caused by low potassium intake was between 4% and 17% . this study also confirmed the inverse association between potassium intake and the risk of hypertension . metabolic and experimental studies have reported that calcium may play a role in the regulation of blood pressure . significantly decreased or was observed with the consumption over 380.5 mg / day of calcium in this study . recently , we also examined the association of calcium intake and blood pressure and revealed that calcium intake was inversely associated with both sbp and dbp in the 30 - 49-year - old group , according to knhanes iii ( data not shown ) , which coincided with the results of this study . several epidemiological studies have reported that people who have a higher intake of calcium tend to have lower blood pressure . dickinson et al .   conducted a meta - analysis and demonstrated that calcium supplementation is effective in lowering blood pressure and hypertension risk . they analyzed 13 randomized controlled trials and found that participants receiving calcium supplementation , when compared to controls , had a statistically significant reduction in sbp ( mean difference : -2.5 mmhg , 95% ci : -4.5 mmhg to -0.6 mmhg ) but not in dbp ( mean difference : -0.8 mmhg , 95% ci : -2.1 mmhg to 0.4 mmhg ) . another meta - analysis also combined 40 clinical trials and revealed that calcium supplementation ( mean daily dose : 1,200 mg ) reduced sbp by -1.86 mmhg and dbp by -0.99 mmhg . a higher dietary calcium intake reduced the risk of hypertension in women over the age of 45 in the american women 's health study , and a calcium intake over 1,000 mg / day lowered the risk of hypertension ( multivariate relative risk = 0.87 ) . also , the appropriate intake levels of sodium , along with a calcium intake of 800 mg or more , reduced the hypertension risk in normotensive or non - treated hypertensive populations , to that of treated hypertensive populations , respectively . in conclusion , we found that calcium and potassium intake were associated with prevalence of hypertension in chungcheong province , respectively . adequate calcium and potassium intake should be encouraged and regional differences should be considered in making a healthy plan for hypertension management .
regional differences between large cities and rural areas are observed in the korean national health and nutrition examination survey ( knhanes ) . 
 this present study was conducted to evaluate the effect of dietary factors on hypertension risk in korean populations , especially residents of the chungcheong province which was not in metropolitan area , using knhanes iii . 
 a total of 544 adults aged  19 years were placed into either the normotensive or the hypertensive group . 
 subject characteristics , bmi , blood pressure , and nutrient intakes were compared between the two groups using a chi - square test and t - test . 
 we estimated odds ratios ( ors ) using multiple logistic regression , adjusted for energy intake and selected covariates . 
 there were significant differences in age , education level , alcohol consumption , and bmi between the normotensive and hypertensive groups . 
 we found decreased ors for the medium versus lowest tertile of calcium intake ( multivariate or = 0.43 , 95% ci : 0.21 - 0.88 ) , for the highest versus lowest tertile of calcium intake ( multivariate or = 0.43 , 95% ci : 0.20 - 0.90 ) with significant trends in risk ( p = 0.040 ) , and for the medium versus lowest tertile of potassium intake ( multivariate or = 0.43 , 95% ci : 0.20 - 0.89 ) . 
 subjects with the highest sodium / calcium ratio had a 2.10-fold greater risk of hypertension compared to the subject with the lowest , with significant trends in risk ( p = 0.002 ) . 
 adequate calcium and potassium intake should be encouraged and regional differences should be considered in making a healthy plan for hypertension management .