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Gender- and Age-Specific Prevalence of Metabolic Syndrome Among Korean Adults: Analysis of the Fifth Korean National Health and Nutrition Examination Survey

Park, Eunok PhD, RN; Kim, JinShil PhD, RN

The Journal of Cardiovascular Nursing: May/June 2015 - Volume 30 - Issue 3 - p 256–266
doi: 10.1097/JCN.0000000000000142
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Background: Despite the growing prevalence of metabolic syndrome (MetS) in Korea, information is lacking on gender- and age-specific patterns in prevalence of MetS among Korean adults.

Aims: The aims of this study were to examine (1) gender-specific prevalence of MetS by its component abnormalities, (2) the prevalence of MetS and its component abnormalities by gender and 10-year age groups, and (3) gender-specific lifestyle risk factors for MetS presentation among Korean adults.

Methods: A secondary data analysis was performed using the most recent national survey. A sample group of 5760 adults (mean age, 44.6 ± 0.46 years; 43.5% men) completed household interviews to provide blood (for high-density lipoprotein cholesterol, triglyceride, and glucose) and anthropometric measurements (ie, waist circumference, weight, and height) to define MetS, as well as data on lifestyle risk factors.

Results: Approximately 1 in 4 Korean adults met the MetS diagnostic criteria. Given each component abnormality, MetS was the most prevalent in men with low high-density lipoprotein cholesterol (63.4%), followed by abdominal obesity (62.3%). In women, it was most prevalent in those with hypertriglyceridemia (73.2%), followed by hyperglycemia (69.7%). Metabolic syndrome showed an association with advanced age for both men and women (P < .001 for both), with greater prevalence of MetS in young and middle-aged men than in women (6.7%–39.9% vs 3.3%–36.4%); these patterns were reversed in people 60 years or older (34.0%–40.5% vs 55.2%–64.1%). Gender-specific lifestyle risk factors for MetS presentation showed a significant association with heavy alcohol drinking and obesity for both men (odds ratio, 1.65 and 5.26, respectively; P < .001 for both) and women (odds ratio, 1.96 and 5.94; P < .042 and < .001, respectively).

Conclusions: Metabolic syndrome is prevalent in a representative sample of Korean adults, with gender- and age-specific patterns. These results are helpful in identification of vulnerable subgroups at high risk for MetS, providing a basis for promotion of cardiovascular health and risk management of MetS.

Eunok Park, PhD, RN Professor, College of Nursing, Jeju National University, South Korea.

JinShil Kim, PhD, RN Associate Professor, College of Nursing, Gachon University, Incheon, South Korea.

The authors have no funding or conflicts of interest to disclose.

Correspondence JinShil Kim, PhD, RN, Gachon University, College of Nursing, 191 Hambakmoero, Yeonsu-gu, Incheon, South Korea (blushil68@gmail.com).

Cardiovascular disease (CVD) is the second leading cause of death in South Korea.1 In particular, individuals with metabolic syndrome are vulnerable to premature death and are at increased risk for developing CVD.2–5 The prevalence of metabolic syndrome has increased worldwide and also in Korea.2,6–8 Approximately 20% to 30% of adults in most countries have metabolic syndrome.9,10 In Korea, data from the Korean National Health and Nutrition Examination Survey (KNHANES) indicate that the prevalence of metabolic syndrome increased from 24.9% in 1998 to 31.3% in 2007 among Korean adults 20 years or older.11

Metabolic syndrome is a cluster of interrelated risk factors for diabetes mellitus and CVD.12 These risk factors include obesity, high triglyceride level, low high-density lipoprotein (HDL) cholesterol level, high blood pressure (BP), and hyperglycemia.12,13 However, different diagnostic criteria have been used over the past decade.10,12,14–19 The prevalence of metabolic syndrome varies depending on the applied definitions.2 One of the major differences among those diagnostic definitions was the abdominal obesity cutoff values.12,20–22 The need to redefine obesity has been recognized in that the current diagnostic criterion of abdominal obesity may not fit Asians or Pacific Islanders, whose metabolic profiles increase with smaller waist circumference.21,23,24 In an attempt to unify criteria for the diagnosis of metabolic syndrome, a multidisciplinary team proposed a harmonized definition in a 2009 Joint Scientific Statement.12 This definition incorporated population- and country-specific cutoff values for waist circumference; however, abnormality in waist circumference is not mandatory for the diagnosis of metabolic syndrome as it is in the International Diabetic Federation definition.20,22 Using the Joint definition, metabolic syndrome can be determined with 3 or more abnormal findings out of 5 criteria. Three of the components (ie, hypertriglyceridemia, hypertension, and hyperglycemia) use a single cutoff point regardless of gender; the remaining 2 components (ie, abdominal obesity and low HDL cholesterol) use gender-specific cutoff points.12

Despite the growing prevalence of metabolic syndrome in Korea, information is lacking on gender-and age-specific differences in the prevalence of metabolic syndrome and its components. The prevalence of metabolic syndrome has been reported to differ by gender.8,18,25–27 Gender differences may also show age variation.27 In past studies, lifestyle risk factors also had gender-specific presentations.28,29 Metabolic syndrome was more prevalent in men than in women, whereas its escalation in women was found to be associated mainly with obesity-driven risks for metabolic syndrome.29 In the overall report of the fifth National Health and Nutrition Survey, which presented major disease morbidities but was lacking in metabolic syndrome and lifestyle behavioral risk factors, men had greater exposure to risks of smoking, heavy alcohol drinking, and obesity, whereas women were more likely to have the risk factor of lack of physical activity.28 Thus, the underlying lifestyle cardiovascular risk factors, including smoking, heavy alcohol drinking, lack of physical activity, overweight, and obesity, and a high stress level should be addressed by gender and age patterns in metabolic syndrome.4,26,29,30

More evidence is needed to estimate the prevalence of metabolic syndrome, applying unified diagnostic criteria, such as the 2009 Joint Scientific Statement.12 In addition, it is important to determine whether gender- and age-specific patterns exist in the prevalence of metabolic syndrome, which may assist in the identification of patients at high risk for metabolic syndrome and potential risk for development of CVD. Gender-specific risk factors for metabolic syndrome presentation are also helpful in establishing risk management for prevention of metabolic syndrome. Therefore, the purpose of this study was to examine the prevalence of metabolic syndrome and each component abnormality by gender and age groups among Korean adults, using the most recent national data. Specific aims were to examine (1) gender-specific prevalence of metabolic syndrome by its component abnormalities, (2) the prevalence of metabolic syndrome and its component abnormalities by gender-stratified 10-year age groups, and (3) gender-specific lifestyle risk factors for presentation of metabolic syndrome among Korean adults 20 years or older.

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Methods

Design

A secondary data analysis was performed in this study. Data were obtained from the first year survey of the fifth KNHANES (KNHANES V-1) conducted in 2010. The Korea Center for Disease Control and Prevention (KCDC) conducted the KNHANES to assess the health and nutritional status of the South Korean population. Participants were recruited using stratified, multistage cluster sampling. Sampling units were selected based on geographical area and residential condition. Subjects were then selected using a systematic sampling method from the clusters. Sampling representative of the South Korean population was ensured with assignment of weighted values to each respondent for an equal sampling probability. Among a total of 10 938 individuals who were sampled, 8473 (77.3%) participated in this national survey. For this study, 5760 subjects 20 years or older were included who completed measurement of anthropometry (waist circumference, weight, and height), blood studies, and BP.

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Procedure

This survey was reviewed and approved by the institutional review boards of the university and the KCDC. The current study used raw data from the KNHANES V-1 without subject contact. After obtaining permission from the KCDC, data were directly downloaded and were protected with a password.

All participants were asked to sign an informed consent statement before data collection. Participants were interviewed by trained interviewers at mobile medical centers. Demographic, socioeconomic, dietary, and health history questions were asked during interviews. Standardized medical examinations were performed by well-trained examiners at mobile medical centers. These medical examinations included waist circumference, HDL cholesterol, triglyceride, BP, and glucose, which were needed to define metabolic syndrome. To address the study aims, prevalence estimates of metabolic syndrome were reported by gender-stratified 10-year age groups. The 10-year age groups were selected based on age stratification strategies often used in past studies.31,32

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Measurement

The 2009 Joint Scientific Statement was used as a reference for metabolic syndrome.12 In the Joint Scientific Statement, clinical definition of the metabolic syndrome requires the presence of 3 or more of the following 5 criteria: (1) elevated waist circumference (abdominal obesity), greater than 90 cm in men and greater than 80 cm in women for Asians; (2) high triglyceride level, 150 mg/dL or greater (≥1.7 mmol/L) or drug treatment for lowering triglycerides; (3) low HDL cholesterol level, less than 40 mg/dL (<1.0 mmol/L) for men and less than 50 mg/dL (<1.3 mmol/L) for women or drug treatment for increasing HDL cholesterol; (4) high BP, systolic 130 mm Hg or higher or diastolic 85 mm Hg or higher or antihypertensive drug treatment in a patient with a history of hypertension; and (5) high fasting glucose, 100 mg/dL or higher or drug treatment for lowering glucose in a patient with a history of diabetes mellitus.12

Correspondingly, data used for this study included anthropometry measurement of waist circumference, height, and weight; BP; blood tests for triglyceride, HDL cholesterol, and fasting glucose; lifestyle-related cardiovascular risk factors; and sociodemographic characteristics. Waist circumference was measured to the nearest 0.1 cm at the midpoint between the highest point of the iliac crest and the lower borders of the rib cage at the midaxillary line at the end of normal expiration. Weights were measured to the nearest 0.1 kg using a calibrated balance beam scale. Heights were gauged using a portable stadiometer. Underweight, normal weight, and overweight or obesity were classified by body mass index (BMI) less than 18.5 kg/m2, 18.5 to 24.9 kg/m2, and 25 kg/m2 or higher, respectively. Blood pressure was measured 3 times in the sitting position, with an average of the last 2 measures used for analysis after making an adjustment of −3.5 mm Hg for men and −2.1 mm Hg for women, considering distance between the heart and the arm, where BP is taken. A description of the standard procedure for BP measurement was published previously.33 Standard protocol was also followed for blood testing.33

Data collected on lifestyle-related cardiovascular risk factors included information on smoking, alcohol intake, physical activity, overweight and obesity, and perceived stress. For smoking status, participants were asked whether they were smoking at the time of the survey interview, and, if not, past smoking history was assessed. Information on the smoking amounts of current smokers was also obtained. For screening alcohol use, participants were asked to report alcohol consumed by frequency during the last year and amount per day. Heavy drinkers were then defined as those whose alcohol consumption exceeds 2 times per week and 7 drinks per 1 time (5 drinks for women). As compared with physical inactivity, moderate or vigorous physical activity during the past week was defined as those who participated in (1) moderate activity that caused them to breathe a little harder than usual with time spent 10 minutes or more, 30 minutes or more per day, and 5 or more days per week (moderate) or (2) each strenuous activity that caused them to breathe very hard with time spent 10 minutes or more, 20 minutes or more per day, and 3 or more days per week. For stress assessment, participants were asked to indicate how much stress one experiences in daily life using 4 response options: extremely a lot, very much, moderately, and rarely. Then, a high level of stress was defined as those who are under extreme pressure or significant pressure.

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Data Analyses

Data analysis was performed using SAS 9.2 software with the sampling weights taken for representativeness. All data were presented as gender-specific prevalence of metabolic syndrome by its component abnormalities (percentage and standard error) (aim 1) and gender- and age-specific prevalence of metabolic syndrome and its component abnormalities (aim 2). Chi-square statistics were then computed for examination of the associations between the presence of metabolic syndrome by its component abnormalities in men and women (aim 1) and between metabolic syndrome or its component abnormalities by 10-year age groups in men and women (aim 2). Multivariate logistic regression analysis was performed for estimation of odds ratios (ORs) for each gender-specific lifestyle risk factor for presentation of metabolic syndrome in which smoking, alcohol drinking, physical activity, BMI, and perceived stress were predictor variables in the model after adjustment for age (aim 3). Statistical significance was set at P < .05.

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Results

Sample Characteristics

A total of 5760 Korean adults 20 years or older completed interviews for questionnaires on sociodemographics and lifestyle and behavioral risk factors, blood studies, and measurement of anthropometry and BP. The mean (SD) age of subjects was 44.6 (0.46) years (range, 20–91 years); 43.5% (n = 2508) of subjects were men, 24.3% had an elementary school education or lower, 75.8% were married, 38.8% had no occupation or were not currently employed, 44.5% reported low or moderately low household income, and 2.3% were Medicaid recipients. The most common lifestyle and behavioral risk factor reported by all study participants was lack of physical activity among those who were not engaged in moderate (88.8%) or vigorous (83.7%) physical activity, followed by overweight or obesity (31.7%), high stress (28.4%), and current smoking (27.4%).

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Gender-Specific Prevalence of Metabolic Syndrome

Gender-specific component abnormalities and prevalence of metabolic syndrome are presented in Table 1. Overall, 25.3% of Korean men and 24.0% of women met the Joint definition of metabolic syndrome. The most prevalent abnormality for Korean men was hypertriglyceridemia (40.2%), followed by hypertension (37.7%), hyperglycemia (30.0%), abdominal obesity (increased waist circumference) (24.7%), and low HDL cholesterol (22.8%). For women, the most prevalent abnormality was abdominal obesity (38.9%), followed by low HDL cholesterol (35.6%), hypertension (28.0%), hypertriglyceridemia (23.2%), and hyperglycemia (20.5%). Among those with each component abnormality, 63.4% of men with low HDL cholesterol had metabolic syndrome, followed by abdominal obesity (62.3%), hyperglycemia (59.0%), hypertriglyceridemia (54.1%), and hypertension (52.3%). A total of 73.2% of women with hypertriglyceridemia had metabolic syndrome, followed by hyperglycemia (69.7%), hypertension (63.0%), low HDL cholesterol (53.7%), and abdominal obesity (53.0%).

TABLE 1

TABLE 1

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Age-Specific Prevalence of Metabolic Syndrome by Gender

The age-specific prevalence of metabolic syndrome and each component abnormality by gender is shown in Figure 1. The prevalence of metabolic syndrome increased with advanced age for both Korean men and women. Significant associations were observed between the presence of metabolic syndrome and 10-year age groups (χ2 = 195.12, P < .001 for men; χ2 = 821.19, P < .001 for women). Specifically, for both men and women, the most vulnerable age subgroup for metabolic syndrome was those individuals 60 years or older. For men, compared with women, metabolic syndrome was more prevalent in those 20 to 29 years old (6.7% vs 3.3%, respectively), 30 to 39 years old (18.3% vs 6.3%, respectively), and 40 to 49 years old (27.2% vs 14.5%, respectively). A reverse pattern in metabolic syndrome was observed after age 60 years or older, with greater prevalence in 60- to 69-year old women (40.5% vs 55.2%, respectively) and women 70 years or older (34.0% vs 64.1%, respectively).

FIGURE 1

FIGURE 1

Significant associations were also observed between each component abnormality and 10-year age groups (P < .001 for both men and women) (Table 2). Each age-specific component abnormality of metabolic syndrome is shown in Figures 2 (men) and 3 (women). Metabolic syndrome was substantially higher in the young (20–29-year-olds) and middle-aged (30–39-year-olds) groups of men in most components, except for HDL cholesterol, compared with women in the same age group. The prevalence of low HDL cholesterol increased with advanced age for women across all age groups, with higher HDL cholesterol abnormality in women (23.7% in those 20–29 years old to 61.2% in those ≥70 years old) compared with age-specific HDL cholesterol abnormality in men (15.5% in those 20–29 years old, 33.0% in those 60–69 years old, and 29.8% in those ≥70 years old). In the 40- to 49-year-old and 50- to 59-year-old age groups, metabolic syndrome showed gender variation in component abnormalities, with greater prevalence of hypertriglyceridemia, hypertension, and hyperglycemia in men, whereas abdominal obesity and low HDL cholesterol were more prevalent in women. After age 60 years, it was apparent that women surpass men in prevalence of metabolic syndrome in most component abnormalities, except for hyperglycemia, which showed a similar gender distribution.

TABLE 2

TABLE 2

FIGURE 2

FIGURE 2

FIGURE 3

FIGURE 3

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Gender-Specific Lifestyle Risk Factors for Metabolic Syndrome Presentation

A summary of gender-specific lifestyle risk factors for presentation of metabolic syndrome is shown in Table 3. In both men and women, heavy alcohol drinking and overweight or obesity (BMI ≥25 kg/m2) were found to be significant predictors of metabolic syndrome, whereas smoking, physical activity, and perceived stress were not significant predictors of metabolic syndrome. Specifically, for men, multivariate logistic regression analysis indicated that heavy drinkers were 1.65 times more likely to have metabolic syndrome (OR, 1.65, P < .001). Metabolic syndrome was also more prevalent among those with overweight or obesity, compared with normal-weight men (15.2% vs 43.1%; P < .001), with those with overweight or obesity approximately 5 times as likely to have metabolic syndrome as those with normal weight (OR, 5.26; P < .001).

TABLE 3

TABLE 3

For women, multivariate logistic regression analysis indicated that those with heavy alcohol drinking were approximately twice more likely to have metabolic syndrome than those without this risk factor (OR, 1.96; P = .042). Metabolic syndrome was also more prevalent among those with overweight or obesity, compared with those with normal weight (15.3% vs 51.9%; P < .001). Those with overweight or obesity were approximately 6 times more likely to have metabolic syndrome than those with normal weight (OR, 5.94; P < .001). Although physical activity was not a significant predictor of metabolic syndrome in either men or women, metabolic syndrome prevalence was significantly lower among men who engaged in a moderate level of physical activity than those with a sedentary lifestyle (26.1% vs 19.3%; P = .043). Metabolic syndrome prevalence was significantly lower among women who engaged in vigorous physical activity, compared with those who did not engage in physical activity (18.0% vs 24.8%; P = .016).

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Discussion

This study is 1 of the few studies that investigated the prevalence of metabolic syndrome in a representative sample of Korean adults, with a focus of investigation of gender- and age-specific patterns in the prevalence of metabolic syndrome and each component prevalence, applying the harmonized diagnostic criteria of the 2009 Joint Scientific Statement. Gender-specific lifestyle risk factors for presentation of metabolic syndrome were also examined. Approximately 1 in 4 Korean adults had metabolic syndrome. Gender-specific patterns in metabolic syndrome were found to exist. The most prevalent metabolic syndrome component was low HDL cholesterol for men and hypertriglyceridemia for women. Age-specific patterns were also observed and showed an increase with advanced age for both men and women. People 60 years or older represented the most vulnerable subgroup to metabolic syndrome overall, but metabolic syndrome was more prevalent in the young and middle-aged groups of men, whereas its age-specific patterns by gender were reversed in most component abnormalities after age 60 years. Gender-specific lifestyle risk factors for presentation of metabolic syndrome also emerged, in that for both men and women, heavy alcohol drinking and BMI of 25 kg/m2 or higher were more likely associated with the development of metabolic syndrome.

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Prevalence of Metabolic Syndrome in Korea

The prevalence of metabolic syndrome in Korean adults was lower than that of adults in the United States.19,20,25,30 In the current study, 25% of Korean men and 24% of women met the Joint definition of metabolic syndrome. In previous studies, the prevalence rates of metabolic syndrome varied by the definitions used.11,20,24,31 On the basis of data from the 2003–2006 National Health and Nutrition Examination Survey, approximately 34% of adult population in the United States met the criteria for metabolic syndrome, and age-adjusted prevalence was 35.1% for men and 32.6% for women using the National Cholesterol Education Program (NCEP) Adult Treatment Panel III guidelines.30,31 Different diagnostic applications to the same dataset (2003–2006 national survey) resulted in 34.3% of prevalence of metabolic syndrome when using 102 cm for men and 88 cm for women as cutoff values for waist circumference, and 38.5% met the Joint definition using the International Diabetes Federation criteria for waist circumference of 94 cm/80 cm for white, African American, and others and 90 cm/80 cm for Mexican American and other Hispanics.20 Based on data from the 1998, 2001, 2005, and 2007 KNHANESs in Korea, age-adjusted prevalence of metabolic syndrome in Korean adults ranged from 24.9% in 1998 to 31.3% in 2007 when applying the revised NCEP criteria.11 The trends in these increases in metabolic syndrome for 10 years are likely to be attributable to more dyslipidemia and abdominal obesity in Korean adults.11 In another study using a sample of metropolitan-dwelling Korean adults (269 men and 505 women) in 1997, 29.0% of men and 16.8% of women met the NCEP Adult Treatment Panel III definition of metabolic syndrome with the Asian-Pacific waist circumference criteria.24

These variations in the metabolic syndrome prevalence are derived primarily from its definition, particularly associated with diagnostic cutoff values for abdominal obesity.12,20–22 Recognition of the need to redefine obesity and abdominal obesity for incorporation into metabolic profiles, particularly for Asian populations, whose body structures are relatively smaller, is required.21,23,24 Racial- or ethnic-specific features in waist circumference have been reflected in the evolution of the definition of metabolic syndrome,21,24 leading to consensus among investigators for establishment of a unified Joint definition of metabolic syndrome.12 Advantages of the Joint definition include that country- and population-specific thresholds seem to be appropriate for detection of metabolic syndrome, particularly among Asian populations.20 The Joint definition is preferred to other definitions because its application eliminates diagnostic inconsistency of metabolic syndrome across populations and countries and subsequently enables researchers to compare the country- and population-specific prevalence of metabolic syndrome.20 Through defining evolution of metabolic syndrome, awareness of metabolic syndrome as a major public health problem has increased over the past decade; yet, estimates of metabolic syndrome vary. An accurate estimate is critical with application of a harmonized set of diagnostic criteria, such as the 2009 Joint definition.12 Its trajectory should also be monitored to raise public and professional attention as it reaches an epidemic proportion. More evidence is needed for a provisional basis for public education on prevention or lifestyle-related risk management interventions of metabolic syndrome.

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Gender- and Age-Specific Trends in Metabolic Syndrome

One of the important findings of this study was that there are gender- and age-specific patterns in the prevalence of metabolic syndrome. In particular, metabolic syndrome increased with advanced age in women and reached a dramatic increase in the 60s and the highest prevalence in the 70 years or older group. This pattern was relatively complex in Korean men, demonstrating continuing increases in the age groups of 20- to 29-year-olds to 50- to 59-year-olds, reaching a plateau in the age groups of 50- to 59-year-olds and 60- to 69-year-olds, followed by a decline in the 70 years or older group. In addition, age-specific patterns in metabolic syndrome indicated that men had higher prevalence than women did in the age groups of 20- to 29-year-olds to 50- to 59-year-olds, whereas prevalence in women showed a marked increase in the 60 years or older group and exceeded the prevalence in men thereafter, with an approximate doubling of prevalence in those 70 years or older.

In previous studies, gender and age patterns in metabolic syndrome were consistent. Similar to our results, the prevalence of metabolic syndrome in women surpassed that of men; however, this pattern presented at an earlier age group of those in their 50s in Korean adults who participated in the KNHANESs.11 The BMI-adjusted prevalence of metabolic syndrome with Asian-Pacific waist circumference criteria also indicated that metabolic syndrome increased with advanced age in both men and women, whereas women surpassed men in prevalence at the age of 60 years and thereafter (19.7% in age <40 years to 45.5% in Korean men aged ≥60 years; 4.3% in age <40 years to 50.0% in women age ≥60 years).24 This pattern was also reported in a representative sample of adults in the United States, with greater prevalence of metabolic syndrome in women than in men at age 70 years and thereafter.34 In addition, during the 14-year follow-up period, significant associations between gender- and age-specific variation in metabolic syndrome and greater all-cause mortality were found in younger adults for both men and women (hazard ratios, 2.53 and 4.22 for men and women, respectively), whereas in older adults, older women only (hazard ratio, 1.44).27 More empirical evidence is needed to identify vulnerable subgroups of metabolic syndrome with regard to gender-age patterns and for examination of its impact on health outcomes.

The prevalence of metabolic syndrome showed age-specific patterns across age groups by gender. Metabolic syndrome continued to increase with a dramatic escalation observed in every 10-year age group in all 5 components among women. For men, hypertension and hyperglycemia increased with age, whereas irregular patterns were observed for abdominal obesity, hypertriglyceridemia, and low HDL cholesterol. It is noteworthy that men showed a relatively higher prevalence of metabolic syndrome at a younger age (20–39 years) than women did in the same age group in most component abnormalities, except for HDL cholesterol, whereas metabolic syndrome showed gender variations, with more component abnormalities found in triglyceride, BP, and glucose in middle-aged men and in waist circumference and HDL cholesterol in middle-aged women. After 60 years of age, the most prevalent component abnormality was hypertension for both men and women and the second next prevalent component abnormality was hyperglycemia for men and abdominal obesity for women.

Consistent with previous reports,11,35 in the current study, dyslipidemia (high triglyceride or low HDL cholesterol) and abdominal obesity were major attributable factors to metabolic syndrome. Hypertriglyceridemia and low HDL cholesterol were the most prevalent component abnormality in young and middle-aged Korean men and women, respectively; abdominal obesity followed as the second most common component abnormality in both middle-aged Korean men and women. Then, abdominal obesity became the most prevalent component abnormality in women 40 to 59 years old, which is still the second leading risk in elderly women. In previous studies using data from 1998, 2001, 2005, and 2007 KNHANES,11,35 gender- and age-specific patterns in abdominal obesity were reported in that prevalence of obesity increased in men with advanced age, whereas obesity increased in older women 60 years or older35; dyslipidemia and abdominal obesity have been attributable to increasing prevalence of metabolic syndrome in Koreans for the past 10 years.11

Menopause and associated abdominal obesity of middle-aged women might explain, in part, this phenomenon.24,36,37 Consistent with our finding showing the reversal of metabolic syndrome prevalence, with women having higher prevalence after age 60 years, a previous study also demonstrated this reversal, with the prevalence showing a significant increase with advanced age in both men and women, and after age 60 years, the prevalence was higher in women than in men (45.5% vs 50.0%).24 Of particular interest, a gender differential pattern for waist circumference emerged in the current study, with abnormality of waist circumference reaching a plateau at age 50 years in men, with a noticeable high prevalence of abdominal obesity starting around middle age in women and increasing until age 70 years. A similar pattern was also observed in the previous study, where the peak waist circumference was reached before age 50 years in men and after age 60 years in women.24 A possible explanation for the increased prevalence of metabolic syndrome in middle-aged women could be associated with an effect of middle age or menopause on abdominal obesity.24,36 A more recent study also reported an increased prevalence of metabolic syndrome in women, which showed a restrictive association with metabolic alterations at menopause, with approximately 2.5-fold higher prevalence of metabolic syndrome in postmenopausal women compared with premenopausal women (8.69% vs 21.85%, respectively).37 Overweight and obesity, particularly abdominal obesity of postmenopausal women, imply that public attention should be paid to health promotion targeting middle-aged people and older women.35

In this study, hypertension was the most common component of metabolic syndrome in elderly Koreans. Hypertension was a more prevalent component abnormality in Korean men than in women, with 37.7% of men and 28.0% of women having hypertension. Metabolic syndrome associated with hypertension was doubled in women in their 50s, reached an almost identical prevalence in the 60s, and exceeded the prevalence in men (80.7% vs 62.5%). Hypertension is 1 of the major chronic health problems in elderly people in Korea. The previous study found that sodium intake in the Korean population surpassed twice the recommended amount of daily sodium intake, reporting that the means of sodium intake ranged between 4572.6 and 5498.9 mg/d across 1998–2010.38 High sodium intake might contribute, in part, to such high prevalence of hypertension in Korean adults. In living in an aging society worldwide, prevention or control of high BP becomes critical with regard to promotion of cardiovascular health.

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Gender-Specific Lifestyle Risk Factors for Metabolic Syndrome Presentation

In this study, gender-specific lifestyle risk factors for presentation of metabolic syndrome emerged, in that its likelihood of occurrence showed an association with heavy alcohol drinking and obesity for both men (OR, 1.65 and 5.26, respectively; P < .001 for both) and women (OR, 1.96 and 5.94; P < .042 and < .001, respectively). Heavy alcohol drinking showed a significant association with development of metabolic syndrome in Korean adults, with heavy alcohol drinkers approximately 2 times as likely to have metabolic syndrome as those who were social drinkers. Overweight or obesity (indicated by BMI ≥25 kg/m2) also showed a significant association with development of metabolic syndrome for both men and women, with approximately 5 and 6 times more likelihood, respectively. The association of higher BMI with metabolic syndrome was consistent with a previous report in that among a representative sample of adults in the United States, those who were overweight had approximately 5 times greater risk for metabolic syndrome compared with those with normal weight (OR, 5.2 for men and 5.4 for women; P < .001 for both).36 Metabolic syndrome is highly prevalent worldwide and is likely to increase with an increase in the prevalence of obesity.9,36 Of particular interest, underweight (BMI <18.5 kg/m2) also significantly decreased the risk for metabolic syndrome for both men and women compared with normal weight (OR, 0.13, P < .001 for men; OR, 0.04, P < .001 for women). Conduct of further studies on the implication of normal weight with regard to metabolic syndrome is warranted to educate the public regarding prevention and to provide guidelines for safety of weight control for those with metabolic syndrome.

However, significant associations with other lifestyle risk factors of physical inactivity and smoking were not found in this study, and previous studies from the literature have reported inconsistent results.20,36,39–41 In previous reports examining associated lifestyle risk factors of metabolic syndrome, physical inactivity showed an association with higher risk for metabolic syndrome, with physically inactive persons having a higher prevalence ratio of metabolic syndrome (leisure time physical activity <150 min/wk; P = .001)20 and physically inactive men having 40% greater risk for metabolic syndrome (OR, 1.4; P < .05), but not women (OR, 1.2; P = .13).36 Despite the well-documented association between smoking with its effect on insulin resistance and metabolic syndrome,23,39,40 this relationship was inconsistent with previous reports in the literature, and 1 study found no significant association for current smoking (prevalence ratio, 0.87; P = .115),20 whereas both male and female current smokers were at higher risk for metabolic syndrome (OR, 1.5, P < .05 and OR, 1.8, P < .01, respectively)36 and current smoking amount showed a significant dose-dependent association with metabolic syndrome in a representative sample of Korean adults (P = .023)41 and in community-based Taiwanese (P = .003).23

This inconsistency regarding the risks of physical inactivity and current smoking for metabolic syndrome might be associated with different approaches for measurements and definitions. Relatively simple definitions of physical activity and smoking status used in this study might underestimate their effects on lowering risk for metabolic syndrome. In previous studies, to define physical inactivity, meticulous estimates of physical activity were performed based on duration, frequency, and intensity, with specific guidelines for types of moderate and vigorous physical activity20 or physical activity density rating scores with gender-specific adjustment during the past month.36 The effect of smoking status on metabolic syndrome was also likely to be significant when considering dose-dependent association.23,41

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Conclusions

In the current study, gender and age patterns in the prevalence of metabolic syndrome emerged from a representative sample of Korean adults. Approximately 1 in 4 Korean adults meets the diagnostic criteria for metabolic syndrome. Given each component abnormality, metabolic syndrome was substantially higher in men with low HDL cholesterol and abdominal obesity and in women with hypertriglyceridemia and hyperglycemia. Metabolic syndrome also showed increasing patterns with advanced age across every 10-year age group for both Korean men and women, with the group of individuals 60 years or older being the most vulnerable to metabolic syndrome. More importantly, men had higher prevalence in the age groups of 20- to 29-year-olds to 50- to 59-year-olds than women in the same age groups, reaching a plateau in the 50- to 59-year-olds to 60- to 69-year-olds, followed by a slight decline in the 70 years or older age group, whereas marked escalations of metabolic syndrome started in the 50- to 59-year-old age group in women, exceeding the prevalence in men at 60 years or older. In the current study, significant lifestyle risk factors for metabolic syndrome included heavy alcohol drinking and overweight or obesity in both men and women.

These results have several clinical implications and provide a basis for promotion of cardiovascular health. Understanding of gender and age patterns in the prevalence of metabolic syndrome and its component prevalence is helpful in the identification of vulnerable subgroups and for establishment of prevention or effective management of metabolic syndrome in various healthcare environments. Information obtained from this study will also be helpful in the design of interventions tailored to gender- and age-specific risk for metabolic syndrome. Tailored interventions and education by gender and age could enhance health outcomes. Research priorities include, but are not limited to, further investigation of gender and age trends in metabolic syndrome with incorporation of lifestyle risk factors; examination of the mechanism for these trends, particularly a dramatic increase in the prevalence of metabolic syndrome in middle-aged women; and development and testing of the effect of a customized intervention for prevention or management of metabolic syndrome.

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What’s New and Important

  • This study investigated gender- and age-specific patterns in the prevalence of metabolic syndrome and each component’s prevalence in a representative sample of Korean adults, applying the harmonized diagnostic criteria of the 2009 Joint Scientific Statement.
  • Approximately 1 in 4 Korean adults had metabolic syndrome. Gender-specific patterns apparently exist. Given each component abnormality, the most prevalent metabolic syndrome component was low HDL cholesterol for men and hypertriglyceridemia for women.
  • Age-specific patterns were also observed and showed an increase with advanced age for both men and women: Metabolic syndrome was more prevalent in the young and middle-aged groups of men, whereas its age-specific patterns by gender were reversed in most component abnormalities after age 60 years.
  • Gender-specific lifestyle risk factors for presentation of metabolic syndrome also emerged, in that heavy alcohol drinking and a BMI of 25 kg/m2 or higher were more likely associated with development of metabolic syndrome.
  • Implications of these results for practice include helping to identify vulnerable subgroups at high risk for metabolic syndrome and providing a provisional basis for promotion of cardiovascular health or risk management for prevention of metabolic syndrome, accordingly.
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Keywords:

cardiovascular disease; Korea; lifestyle risk factors; metabolic syndrome; prevalence

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