Prevalence of Low HDL-Cholesterol Levels and Associated Factors Among Koreans

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1 Circ J 2006; 70: Prevalence of Low HDL-Cholesterol Levels and Associated Factors Among Koreans Seon Mee Kim, MD; Jee Hye Han, MD*; Hye Soon Park, MD** Background Low levels of high-density lipoprotein cholesterol (HDL-C), as well as high levels of low-density lipoprotein cholesterol, play a crucial role in the development of cardiovascular disease, which has shown a remarkable increase in Korea. Method and Results Data were obtained from the 1998 Korean National Health and Nutrition Examination Survey, which was a cross-sectional national health survey. The total study population amounted to 7,300 individuals (3,283 men, 4,617 women), aged 18 years and older. The prevalence of low HDL-C levels, as proposed by National Cholesterol Education Program Adult Treatment Panel III or International Diabetes Federation, was 23.8% in men and 47.5% in women. After adjusting for independent variables, there was a greater risk of low HDL-C with an increased body mass index, abdominal obesity, cigarette smoking, and decreased alcohol consumption. Physically inactive lifestyle in men and low fat intake in women were identified as factors associated with low HDL-C level. Conclusions The prevalence of low HDL-C levels is relatively high among Koreans, which may have important implications for public health. Identified associated factors should be considered for reducing the risk of low HDL-C levels in Koreans. (Circ J 2006; 70: ) Key Words: Alcohol; High-density lipoprotein cholesterol; Obesity; Smoking Epidemiological studies have shown that high-density lipoprotein cholesterol (HDL-C) levels are inversely related to the incidence of cardiovascular disease (CVD) in both women and men. 1 3 Low HDL-C levels, as well as high low-density lipoprotein cholesterol (LDL-C) levels, play a crucial role in the development of CVD, and subjects with low HDL-C (HDL-C <35mg/dl) have a 2.5- to 4.1-fold increased risk of dying from CVD than do subjects with high HDL-C (HDL-C 60 mg/dl). 4 While genes are the major determinants of HDL-C, accounting for about 50% of the level, 5 environmental factors such as obesity, 6 physical inactivity, 7 alcohol consumption, 8,9 cigarette smoking, 9 11 and dietary factors 12 also play significant roles. The inverse association between HDL-C levels and CVD constitutes a continuous pattern, 13 and so its threshold cannot be identified. Not only the National Cholesterol Education Program Adult Treatment Panel (NCEP ATP) III, 14 but also International Diabetes Federation (IDF) 15 proposed that a level of HDL-C <40 mg/dl in men and <50 mg/dl in women beclassified as a low HDL-C level, which is one of components to be satisfied in the definition of metabolic syndrome. Those values are more strict than the ones suggested by NCEP ATP II, 16 which proposed the criteria of low HDL-C as <35 mg/dl in both genders. Several investigators have reported previously that HDL-C levels are lower in Asian populations than in (Received November 11, 2005; accepted May 1, 2006) Department of Family Medicine, College of Medicine, Korea University, *Department of Family Medicine, Eulji Hospital, Eulji University School of Medicine and **Department of Family Medicine, Asan Medical Center, Ulsan University College of Medicine, Seoul, Korea Mailing address: Professor Hye Soon Park, MD, PhD, MPH, Department of Family Medicine, Asan Medical Center, University of Ulsan College of Medicine, Poongnap-dong Songpa-gu, Seoul , South Korea. hyesoon@amc.seoul.kr European and American populations, although Asians are less obese Interpopulation differences in HDL-C levels are considered to be the main factor causing this difference, 18,19 but they cannot totally explain this effect. However, the prevalence of, and modifiable lifestyle factors that have been associated with, low HDL-C have not been investigated fully among Asian populations. In Korea, like other Asian countries, CVD has shown a remarkable increase. 20 Therefore, we investigated the prevalence of low HDL-C levels in the general Korean population, as well as modifiable lifestyle factors associated with low HDL-C among Koreans. Methods Study Population Our research was based on the 1998 Korean National Health and Nutrition Examination Survey (KNHANES), a cross-sectional, nationally representative study. 21 We used a stratified multistage probability sampling design, making selections from sampling units based on geographic area, sex, and age groupings from the household registries. A total of 10,876 people over the age of 10 years were identified as potential participants in our study. Of these, we excluded 1,105 individuals, including those for whom we had no anthropometric measurements, those who had fasted incorrectly prior to the blood test, and those who missed the nutritional interview. In addition, 2,471 individuals who were less than 18 years of age were excluded. The data of 7,300 respondents were available for analysis. Anthropometric Measurements and Cardiovascular Risk Factors Height was measured to 0.1 cm using a portable stadiometer (850 2,069 mm; Seriter ), and weight was measured

2 Low HDL-C Levels in Koreans to the nearest 0.1 kg using a balance beam scale (Giant- 150N; HANA ). Body mass index (BMI) was calculated by dividing weight (kg) by height 2 (m 2 ). Waist circumference (WC) was measured at the midpoint between the lower border of the rib cage and the iliac crest. BMI was divided into 5 categories: <18.5, , 23 25, 25 27, and 27 kg/m 2. WC was divided into tertiles arbitrarily: <79, 79 86, and 86 cm in men, and <73, 73 81, and 81 cm in women, respectively. A mercury sphygmomanometer (Baumanometer ) was used to measure the blood pressure of each subject while seated after a 10min rest. Blood samples were obtained from an antecubital vein into vacutainer tubes containing EDTA, in the morning following a 12-h overnight fast. The samples were subsequently analyzed at a central, certified laboratory. Total cholesterol, triglyceride, and HDL-C were measured by autoanalyzer (Hitachi 747 auto-analyzer, Japan). LDL-C was calculated by Friedewald equation if triglyceride was <400 mg/dl. Lifestyle Factors Components of socioeconomic status (ie, education, economic level, or occupational status) were obtained by interview. Educational background was determined in terms of the total years of education and was classified as <7 years, 7 9 years, years, and >12 years of education. Economic level was divided into 4 groups by monthly income. Occupational status was grouped into 3 categories: white collar (professional, administrative, office work, or service job); blue collar (agricultural, fishing, industrial, or other manual job); and unemployed (including students and women who worked in their homes without pay). Dietary intake was assessed by the single 24-h dietary recall method. All subjects were requested to maintain their usual diet before testing. Food models were used to estimate the portion sizes. The record for each subject was coded, and standard reference tables were used to convert household portions to grams. Record nutrient analysis was performed using a computerized program (CAN, Korea Nutrition Society, Seoul, Korea). 23 As one relevant measure of dietary composition, fat intake was selected and expressed as a percentage of the total food energy. Self-reported alcohol, smoking, and physical activity were determined from the questionnaires. Alcohol consumption was estimated from the subjects usual daily intake of alcoholic beverages. Drinking was divided into 4 groups by the amount of alcohol consumed: none, <15 g/day, g/day, and 30 g/day. With respect to smoking, individuals were classified according to whether the respondent was a non-smoker, an ex-smoker, or a current smoker. Participants were also asked about the frequency and extent of their physical activity on a weekly basis, including the intensity of daily activity, sports, physically active hobbies, and fitness exercises over the previous 30 days. Physical activity was categorized into 4 groups: sedentary, light, moderate, and high. Definitions In the present study, we used the definition of low HDL- C proposed by NCEP ATP III 14 or IDF, 15 fasting HDL-C <40 mg/dl in men, <50 mg/dl in women. We used the definition of metabolic syndrome proposed by NCEP ATP III, as the presence of 3 or more of the following risk factors: (1) central obesity, 23 WC >90 cm in men and >80 cm in women; (2) hypertriglyceridemia, fasting plasma triglycerides 150 mg/dl; (3) low HDL-C, Table 1 Basic Characteristics of the Study Population Men (n=3,283) Women (n=4,017) Mean±SD Mean±SD Age (years) 41.5± ±17.5 BMI (kg/m 2 ) 23.1± ±3.4 WC (cm) 81.9± ±9.9 Total cholesterol (mg/dl) 183.4± ±37.9 HDL-C (mg/dl) 48.3± ±12.5 Triglyceride (mg/dl) 130.5± ±55.2 LDL-C (mg/dl) 111.4± ±33.2 Total calorie (kcal) 2,289.0± ,796.1±772.4 Fat (%) 16.1± ±8.9 Age (years) (26.2) 1,052 (25.2) (23.6) 888 (22.1) (18.8) 698 (17.4) (14.1) 559 (13.9) (11.5) 490 (12.2) (5.7) 330 (8.2) BMI (kg/m 2 ) < (6.4) 262 (6.5) ,555 (47.4) 1,879 (46.8) (22.7) 809 (20.1) (14.3) 587 (14.6) (9.2) 406 (12.0) WC (cm)* Lower tertile 1,103 (33.6) 1,352 (33.7) Middle tertile 1,092 (33.3) 1,321 (32.9) Higher tertile 1,088 (33.1) 1,344 (33.5) Residential area Large city 1,274 (38.8) 1,509 (37.6) Medium city 778 (23.7) 954 (23.8) Rural 1,231 (37.5) 1,554 (38.7) Marital status Married 2,348 (71.5) 2,604 (64.8) Unmarried 840 (25.6) 750 (18.7) Others 95 (2.9) 663 (16.5) Education (years) <7 641 (19.5) 1,410 (35.1) (14.6) 562 (14.4) ,362 (41.5) 1,402 (34.9) (24.4) 643 (16.0) Occupation White collar 1,070 (32.6) 946 (23.6) Blue collar 1,420 (43.3) 954 (23.8) Unemployed 793 (24.2) 2,117 (52.7) Income (US$/month) < (20.4) 933 (23.2) 500 1, (30.1) 1,171 (29.2) 1,000 2,000 1,217 (37.1) 1,401 (34.9) 2, (12.5) 512 (12.8) Alcohol (g/day) None 973 (29.6) 2,161 (53.4) < (11.6) 960 (23.9) (22.3) 653 (16.3) 30 1,197 (36.5) 243 (6.1) Smoking None 925 (28.2) 3,687 (91.8) Ex-smoker 526 (16.0) 99 (2.5) Current-smoker 1,832 (55.8) 231 (5.8) Physical activity Sedentary 891 (27.1) 1,355 (33.7) Light 930 (28.3) 1,468 (36.5) Moderate 1,123 (34.2) 952 (23.7) Heavy 339 (10.3) 242 (6.0) Fat (% of total intake) <12 1,122 (34.2) 1,626 (40.5) ,228 (37.4) 1,281 (31.9) (28.4) 1,110 (27.6) 821 Data are n (%). *WC was divided into tertiles : <79, 79 86, and 86 cm in men, and <73, 73 81, and 81 cm in women, respectively. BMI, body mass index; WC, waist circumference; HDL-C, high-density lipoprotein cholesterol; LDL-C, low-density lipoprotein cholesterol.

3 822 KIM S M et al. Fig 1. Mean high-density lipoprotein cholesterol (HDL-C) level by gender and age groups. Closed bar: men, open bar: women. p for trend <0.05 in women. Fig 2. Frequency of low high-density lipoprotein cholesterol (HDL- C) by gender and age groups. Closed bar: men, open bar: women *p<0.05, p for trend <0.05 in women. fasting HDL-C <40 mg/dl in men, <50 mg/dl in women; (4) hypertension, systolic and/or diastolic blood pressure 130/85 mmhg or known treatment of hypertension; and (5) hyperglycemia, fasting plasma glucose 110 mg/dl or known treatment of diabetes. Statistical Analysis Statistical analyses were performed using the SAS statistical package (version 8.2; SAS Institute Inc, Cary, NC, USA). Baseline variables were described as group means (± SD), in men and women, respectively. HDL-C values were expressed as age- and gender-specific mean, and ageand gender-specific proportions, for prevalence of low HDL-C. A regression analysis was used to test the significance of an increase or decrease of mean HDL-C values across age groups in each gender. A chi-square test was used to examine gender differences, and a test for trend was used to analyze the significance of an increase in prevalence across age groups. Demographic factors (age, residential area, marital status, education level, occupation, and economic status), anthropometric factors (BMI and WC), lifestyle factors (alcohol consumption, cigarette smoking, and physical activity), and nutrition factors (fat intake) were created as dummy variables. Multiple logistic regression analysis was performed to examine the risk of low HDL-C levels (as a dependent variable) according to the demographic, anthropometric, lifestyle, and nutrition factors (as the independent variables) in men and women, respectively. The adjusted odds ratio (OR) was presented together with a 95% confidence interval. Mantel s test was used to perform trend analysis. All reported p-values were based on 2-sided tests and p-values <0.05 were considered significant. Results Basic Characteristics of Study Population The characteristics of the study population, as stratified by gender, are presented in Table1. The average ages of the men and the women were 41.5±16.5 and 42.7±17.5 years, respectively. The mean BMI was 23.1±3.0 and 23.3± 3.4 kg/m 2, respectively, for the men and women. Energy from fat was about 15 16% of the total energy intake for both groups. Urban residents comprised 62% of the study population. Almost one-quarter of the men and one-sixth of the women had received a college education. For men, about 70% of the subjects were drinkers, about 56% were current smokers, and about 45% reported being physically active. For the women, about 50% of the subjects were drinkers, only about 6.6% were current smokers, and about 30% were physically active. Mean HDL-C Values and Prevalence of Low HDL-C The overall mean HDL-C levels were 48.3±12.2 mg/dl for men and 51.7±12.5 mg/dl for women. The age-specific mean HDL-C levels for men increased from age 30 to the decade of the 70 s. However, mean HDL-C levels for women gradually decreased from age 20 to the decade of the 70 s. The mean HDL-C levels were higher in women than in men into the 50s; however, the reverse finding was found in those over 60 years old (Fig 1). According to the criteria of low HDL-C by NCEP ATP III, the prevalence of low HDL-C was 23.8% of men and 47.5% of women. The prevalence of low HDL-C was 20 30% for men in any age group; however, low HDL-C for women gradually increased from 40% for those in their 20 s to 60% for those in their 70 s. The prevalence of low HDL-C was significantly higher in women than in men, for all age groups (Fig2). Cardiovascular Risk Factors According to HDL-C Level Table 2 shows the cardiovascular risk factors according to HDL-C levels. The mean WC, fasting plasma glucose, LDL-C, and triglyceride levels were higher in the subjects with low HDL-C than in those with normal HDL-C levels. Systolic and diastolic blood pressures differed significantly between the 2 groups only for women. Total cholesterol levels were lower in the subjects with low HDL-C than in those with normal HDL-C levels. Subjects with low HDL- C had more abdominal obesity, higher fasting plasma glucose, higher triglycerides, and metabolic syndrome than those with normal HDL-C levels. The prevalence of high blood pressure showed a significant difference between 2 groups only for women.

4 Low HDL-C Levels in Koreans 823 Table 2 Cardiovascular Risk Factors According to HDL-C Levels in Men and Women Men (n=3,283) Women (n=4,017) Normal Low HDL-C Normal Low HDL-C (n=2,512) (n=771) (n=2,109) (n=1,908) Waist circumference (cm) 82.0± ± ± ±9.5 Systolic blood pressure (mmhg) 127.2± ± ± ±20.3 Diastolic blood pressure (mmhg) 81.0± ± ± ±11.3 Fasting plasma glucose (mg/dl) 100.1± ± ± ±31.5 Total cholesterol (mg/dl) 187.8± ± ± ±39.0 HDL-C (mg/dl) 51.8± ± ± ±3.8 LDL-C (mg/dl) 110.7± ±33.2* 111.8± ±34.4 Triglyceride (mg/dl) 126.0± ±67.5* 99.5± ±65.2 Abdominal obesity (%) 18.0 (0.8) 28.8 (1.8) 36.0 (0.9) 55.1 (1.8) High blood pressure (%) 45.1 (1.0) 44.8 (2.0) 27.3 (0.9) 38.0 (1.8) High fasting plasma glucose (%) 19.7 (0.8) 23.4 (1.7)* 15.0 (0.7) 23.1 (1.6) High triglyceride (%) 29.8 (1.0) 57.7 (2.0) 14.5 (0.7) 45.7 (1.8) Metabolic syndrome (%) 11.4 (0.7) 50.4 (2.0) 10.1 (0.6) 51.1 (1.8) Low HDL-C <40 mg/dl for men and <50 mg/dl for women; Abdominal obesity: waist circumference 90 cm for men and 80 cm for women according to Asia Pacific guideline; High blood pressure 130 mmhg or 85 mmhg or treatment of previously diagnosed hypertension; High fasting plasma glucose 110 mg/dl or previously diagnosed type 2 diabetes; High triglyceride 150 mg/dl; Metabolic syndrome; participants having 3 or more of the 5 above components. Data are expressed as mean ± SD or prevalence (SE). *p<0.05, p<0.01 by student s t-test for numeric variables and 2 -test for categorical variables between normal HDL-C groups and low HDL-C groups in men and women, respectively. Abbreviations see in Table 1. Factors Associated With Low HDL-C According to Gender Tables 3 and 4 show the results of multiple logistic analyses for low HDL-C levels for men and women, respectively. The adjusted OR for the low HDL-C levels increased with increments of BMI and WC in both men and women. The adjusted OR for a low HDL-C level was higher for the unemployed than for the employed men. A clear trend of decreased risk for low HDL-C levels was noted with greater intakes of alcohol for both men and women. Current smokers were at a significantly higher risk of low HDL-C levels, compared with non-smokers, for both genders. We found a gradual decrease of the adjusted OR for low HDL-C levels with physical activity in men. Fat intake, expressed as a percentage of total energy consumption, was positively correlated with HDL-C levels, and a graded association for the amounts of consumed fat was noted. This relationship was statistically significant only for women. Discussion In our study, we demonstrated that the prevalence of low HDL-C was 25.3% in Korean men and 48.4% in Korean women using the NCEP ATP III 14 or IDF criteria. 15 The corresponding figures are 35.2% for men and 39.3% for women in the United States, 24 and in Japan, 18.5% for men and 30% for women. 25 Epidemiologic studies have found lower levels of total cholesterol and HDL-C in African and Asian men than in European and American men. 18 The mean HDL-C levels for Korean men and women in this study were 48 mg/dl and 51 mg/dl, respectively. In a comparison of our findings with the data of the National Health and Nutrition Examination Survey III in the United States (1988 through 1991), we found that the mean HDL-C levels were 47mg/dl in men and 56mg/dl in women, 24 with Korean women having lower mean HDL-C levels. In our study, among women, the mean HDL-C levels decreased, and the prevalence of low HDL-C increased, gradually, from the age of 20 to the age of 70. In most countries, mean HDL-C levels are significantly higher in women than in men in all age groups, but in our study, mean HDL-C levels were observed to be lower for women than for men among those over 60 years of age. Changes in body weight might be important determinants of unfavorable changes in HDL-C with aging. 6 Among Koreans, women have a greater BMI and WC than men after 50 years of age. 21 Obesity is a significant CVD risk factor, and excess body weight is closely linked to low serum HDL-C levels. 6 Several studies have reported that obesity is one of the most important factors in reducing HDL-C levels. 6,26 In our data, the OR of low HDL-C levels increased significantly in relation to a higher BMI and WC, for both genders. Components of socioeconomic status (ie, education, economic level, or occupational status) are important risk factors, 27 and may affect HDL-C levels. Our study revealed that the OR for low HDL-C levels increased significantly among unemployed men. At the beginning of the 20th century, CVD was more common in the upper socioeconomic classes than in the lower classes. However, recent largescale epidemiological studies have reported a higher prevalence of CVD among individuals in the lower socioeconomic groupings than in those of the middle or higher socioeconomic strata. 28 Our findings appear to be accordance with those reports only for unemployed men. Moreover, our study shows a significant association between higher HDL-C levels and greater alcohol consumption. Research has shown that alcohol consumption increases HDL-C levels, and that higher alcohol intake is associated with higher levels of HDL-C. 8,9,29,30 Cigarette smoking is associated with lower levels of HDL-C, 9,11,30 and that this association is independent of age, obesity, alcohol consumption, and regular exercise. 31 In our study, we found that current smoking was a significant independent risk factor for low HDL-C levels, for both genders. However, this finding was not seen in ex-smokers of both genders. Physical activity relates significantly to a higher HDL-C level. 28,32 In accordance with these findings, the

5 824 KIM S M et al. Table 3 Adjusted OR for Low HDL-C Level as a Dependent and the Associated Factors as Independent s in Men No. of low HDL-C OR p for (%) (95%CI) trend Age (years) (16.4) (27.8) 1.36 ( ) (26.6) 1.17 ( ) (24.8) 1.02 ( ) (23.8) 1.12 ( ) (29.8) 1.74 ( ) BMI (kg/m 2 ) < (12.8) (17.7) 1.25 ( ) (27.5) 1.54 ( ) (33.3) 1.98 ( ) (39.4) 2.64 ( ) WC (cm) <0.001 Lower tertile 137 (12.4) 1.0 Middle tertile 233 (21.3) 1.86 ( ) Higher tertile 323 (29.7) 1.92 ( ) Residential area Large city 293 (23.0) 1.0 Medium city 191 (24.6) 1.12 ( ) Rural 298 (24.2) 1.21 ( ) Marital status Married 625 (26.6) 1.0 Unmarried 134 (16.0) 0.46 ( ) Others 23 (24.2) 0.82 ( ) Education (years) <7 194 (24.3) (23.4) 1.12 ( ) (24.6) 1.06 ( ) (23.6) 1.12 ( ) Occupation 0.06 White collar 256 (23.9) 1.0 Blue collar 341 (24.0) 1.10 ( ) Unemployed 185 (23.3) 1.40 ( ) Income (US$/month) < (23.5) , (23.2) 1.26 ( ) 1,000 2, (24.4) 1.08 ( ) 2, (24.2) 1.18 ( ) Alcohol (g/day) <0.001 None 248 (25.5) 1.0 < (34.8) 0.88 ( ) (25.4) 0.56 ( ) (18.0) 0.32 ( ) Smoking None 188 (20.3) 1.0 Ex-smoker 128 (24.3) 1.08 ( ) Current-smoker 466 (25.4) 1.48 ( ) Physical activity Sedentary 257 (28.8) 1.0 Light 239 (25.7) 0.82 ( ) Moderate 213 (19.0) 0.72 ( ) Heavy 73 (21.5) 0.65 ( ) Fat (% of total intake) < (24.4) (24.4) 1.28 ( ) (22.3) 1.16 ( ) OR, odds ratio; CI, confidence interval. Other abbreviations see in Table 1. Table 4 Adjusted OR for low HDL-C Level as a Dependent and the Associated Factors as Independent s in Women No. of low HDL-C OR p for (%) (95%CI) trend Age (years) (39.1) (41.7) 1.11 ( ) (50.7) 1.24 ( ) (52.4) 1.02 ( ) (57.4) 1.37 ( ) (60.1) 1.40 ( ) BMI (kg/m 2 ) <0.001 < (39.5) (32.1) 2.61 ( ) (53.8) 3.10 ( ) (58.8) 3.59 ( ) (63.1) 3.58 ( ) WC (cm) <0.001 Lower tertile 154 (11.4) 1.0 Middle tertile 276 (20.9) 1.68 ( ) Higher tertile 423 (31.5) 1.77 ( ) Residential area Large city 645 (42.7) 1.0 Medium city 444 (46.5) 1.03 ( ) Rural 821 (52.8) 1.26 ( ) Marital status Married 1,271 (48.8) 1.0 Unmarried 285 (38.0) 1.00 ( ) Others 354 (53.4) 0.97 ( ) Education (years) (57.0) (49.5) 0.71 ( ) (42.4) 0.84 ( ) (36.2) 0.87 ( ) Occupation White collar 375 (39.6) 1.0 Blue collar 491 (51.5) 0.97 ( ) Unemployed 1,044 (49.3) 0.87 ( ) Income (US$/month) (51.6) , (50.3) 0.98 ( ) 1,000 2, (44.4) 0.86 ( ) 2, (42.3) 0.87 ( ) Alcohol (g/day) None 1,110 (51.4) 1.0 < (45.1) 0.73 ( ) (44.0) 0.71 ( ) (32.9) 0.44 ( ) Smoking None 1,746 (47.4) 1.0 Ex-smoker 42 (42.4) 0.95 ( ) Current-smoker 122 (52.8) 1.37 ( ) Physical activity Sedentary 676 (49.7) 1.0 Light 672 (46.3) 0.92 ( ) Moderate 458 (47.3) 1.03 ( ) Heavy 104 (43.7) 0.74 ( ) Fat (% of total intake) < (54.4) (43.4) 0.94 ( ) (42.3) 0.65 ( ) Abbreviations see in Tables 1,3. present study demonstrated a significant relationship between physical activity and HDL-C in men. Several dietary components also affect HDL-C levels. Higher intakes of fat are associated with higher levels of total cholesterol and HDL-C. 33 Actually, total cholesterol and HDL-C levels were related to each other in the present study (data not shown). Our study showed that fat intake was significantly associated with HDL-C levels; decreasing the intake of fat increases the OR of low HDL-C levels in women. A high-fat, high-cholesterol diet raised HDL-C and the production rate of apoa-i by means of a mechanism that involves the regulation of translation of the apoa-i mrna. 33,34 Compared with populations in the West, whose consumed fat intake is 35 40% of their total diet, 34 Koreans

6 Low HDL-C Levels in Koreans consume relatively little fat because their meals are carbohydrate dominent (eg, rice, noodles etc). This finding may explain, in part, why Koreans have relatively low total and HDL-C levels, as compared with Western countries. 34 A balanced diet may improve low HDL-C in Korean women. Study Limitations The major limitation is the cross-sectional design, which prevented us from establishing casual relationships. Therefore, the results presented here reflect only associations between demographic, anthropometric, lifestyle, and nutrition factors and low HDL-C. We were unable to observe genetic factors that are related to the development of low HDL-C. In this regard, further studies aimed at identifying genetic factors associated with low HDL-C are necessary. Other limitations include the possible misclassification of recall bias and confounding factors. Estimates from a single 24-h recall method cannot be corrected for intra-individual daily variation in consumption. Although single recalls are useful to estimate population means, the variation of intake might, in fact, be under- or overestimated. Additionally, we could not analyze other dietary factors, including particular fatty acids, that might influence HDL-C levels. Similarly, the possible misclassification of alcohol consumption could not be excluded. We could not tell if alcohol drinking is a protective factor for the risk of low HDL-C levels in heavy drinkers, because the original inquiries could not provide more detailed information in drinkers consuming 30 g/day. Conclusion This study demonstrated that the prevalence of low HDL-C was 25.3% in Korean men and 48.4% in Korean women. These levels are rather high, despite a relatively low prevalence of obesity. 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