Abstract
Background Han is the largest and Zhuang is the second largest among the 56 nationalities in China. Geographically and linguistically, Zhuang can be classified into 43 ethnic subgroups, among which Hei Yi (which means “black worship” and “black dressing”) Zhuang is the most conservative group, according to its unique culture and customs. Little is known about the lipid profiles and corresponding risk factors of hyperlipidemia in this population. Therefore, the aim of this study was to compare the effects of demographic characteristics, health-related behaviors, and lifestyle factors on the prevalence of hyperlipidemia for the middle-aged and elderly in the Guangxi Hei Yi Zhuang and Han populations.
Methods A sample of 657 people of Hei Yi Zhuang aged 40 years and over was randomly selected from 7 villages in Napo County, Guangxi, China. Information on demographic characteristics, health-related behaviors, and lifestyle factors was collected by questionnaire. Blood pressure, height, weight, waist circumference, and serum lipid and apolipoprotein (apo) levels were measured, and body mass index (BMI) was calculated as a measure of weight relative to height. The results were compared with those in 520 people of Han living in the same region.
Results The prevalence of hyperlipidemia in the Hei Yi Zhuang was significantly lower than that in the Han (36.2% vs 42.3%; p < .05). The levels of total cholesterol, triglyceride, low-density lipoprotein cholesterol, and apo B in Hei Yi Zhuang were also significantly lower than those in the Han (p < .05 to .001), but the levels of high-density lipoprotein cholesterol and the ratio of apo A-I to apo B in the Hei Yi Zhuang were significantly higher than those in the Han (p < .01 and < .001, respectively). There were no significant differences in apo A-I levels between the two ethnic groups (p > .05). The prevalence of hyperlipidemia was positively correlated with BMI and blood pressure in the Hei Yi Zhuang. Hyperlipidemia was positively associated with age, BMI, and blood pressure and negatively associated with gender (female higher) in the Han.
Conclusions In the present study of the middle-aged and elderly population, the Hei Yi Zhuang have a more favorable lipid profile and a lower prevalence of hyperlipidemia than do the Han, and there is also a significant difference in the risk factors for hyperlipidemia between the two ethnic groups, which might result from the effects of different demographic characteristics, health-related behaviors, and lifestyle factors.
Research from animal, epidemiologic, and genetic disorder studies indicates that elevated plasma or serum levels of cholesterol,1,2triglycerides (TG),3,4low-density lipoprotein cholesterol (LDL-C),5,6and apolipoprotein (apo) B7,8are all considered to be independent risk factors of coronary heart disease. A great deal of research effort has been focused on the determinants of these risk factors. Currently, it is well accepted that environmental factors, such as diet,9,10cigarette smoking,11,12and physical activity,13,14and genetic factors15,16are involved in determing the levels of these lipid phenotypes. In addition, lipid profiles in different ethnic groups may also exhibit differences.17,18Han is the largest nationality and Zhuang is the largest minority among 56 nationalities in China. Geographically and linguistically, Zhuang can be classified into 43 ethnic subgroups, among which Hei Yi (which means “black worship” and “black dressing”) Zhuang, living in Napo County bordering northeast Vietnam and with a population of 51,655, is the most conservative, with a unique culture. Strict intranationality marriages have been performed from time immemorial in this population. Namely, only men and women who are Hei Yi Zhuang can marry; they cannot intermarry with the other groups of Zhuang or other nationalities. Little is known regarding the epidemiologic data of hyperlipidemia in these populations. Therefore, the present study was designed to compare the effects of demographic characteristics, health-related behaviors, and lifestyle factors on the lipid level, the prevalence of hyperlipidemia, and its risk factors for the middle-aged and elderly in the Hei Yi Zhuang and Han populations.
METHODS
Subjects
Six hundred fifty-seven people of Hei Yi Zhuang nationality were randomly selected from seven villages in Napo County, Guangxi Zhuang Autonomous Region, China. The ages of the subjects ranged from 40 to 84 years, with an average age of 56.9 ± 10.7 years. There were 315 males (47.9%) and 342 females (52.1%). All subjects were peasants. One hundred seventy-seven people were ages 40 to 49 years (26.9%), 196 people were 50 to 59 years (29.8%), 196 people were 60 to 69 years (29.8%), 76 people were 70 to 79 years (11.6%), and 12 people were 80 years and over (1.8%). Of 51, 655 people of the Hei Yi Zhuang population who live in 82 villages in Napo County, the subjects accounted for 1.3%. At the same time, 520 people of Han nationality who reside in 9 villages in Napo County were also surveyed by the same method. The mean age of these subjects was 55.8 ± 11.3 years (range 40-89 years). There were 221 males (42.5%) and 299 females (57.5%). All subjects were also peasants. One hundred seventy-three people were ages 40 to 49 years (33.3%), 140 were 50 to 59 years (28.7%), 117 were 60 to 69 years (22.5%), 73 were 70 to 79 years (14.0%), and 8 were 80 years and over (1.5%). All of these subjects were essentially healthy and had no evidence of diseases related to atherosclerosis. The participants had no known medical problems and did not take medications known to affect lipid concentrations, such as β-adrenergic blocking agents, thiazide diuretics, cholesterol-lowering agents, hypoglycemic agents, or hormones. The study was approved by our institutional ethics committee, and the study subjects gave informed consent to participate in the study.
Epidemiologic Survey
The survey was carried out using internationally standardized methods. The medical and family history and socioeconomic and personal information, including demographics, habitual diet, physical activity patterns, drug use, alcohol consumption, smoking habits, occupation, education level, and other lifestyle behaviors, were obtained by questionnaires. The 24-hour dietary recall method was used to determine the dietary intakes of each subject.19Detailed descriptions of all foods, beverages, and supplements consumed during the 24-hour period before the interview, including the quantity, cooking method, and brand names, were recorded by a chief physician. The interviewer used food models and pictures depicting portion sizes and followed a standardized protocol for determining the weight of the food consumed. The intakes of macronutrients from the ingredients were determined by using the 2002 Chinese Food Composition Table.20Physical activity was ascertained with the use of 10 questions designed to measure both leisure and work activities. These questions aimed to quantify the time (hours and minutes) spent in bed (sleeping and resting), performing household activities (cooking and cleaning), and performing discretionary activities (eg, gardening, walking, bicycling, and exercising). Residual time (time not accounted for by the listed activities) was assumed to be spent in light to moderate activities. The physical examination included several anthropometric parameters, such as blood pressure, height, weight, and waist circumference. Blood pressure was measured three times using a mercury sphygmomanometer, and the average of the three measurements was used for the blood pressure level. The measurement was taken on the right arm while the subject was in a sitting position, after at least 5 minutes of rest. The values of systolic pressure were defined as the appearance of the first Korotkoff sound (K1) and the values of diastolic pressure by the appearance of the fifth Korotkoff sound (K5), according to the current recommendations. The weight of each subject was measured with a calibrated scale to the nearest 0.1 kg by a trained technician, and height was measured with use of a portable stadiometer. Waist circumference was measured with a nonstretchable measuring tape, at the level of the smallest area of the waist, to the nearest 0.1 cm. Body mass index (BMI) was calculated as weight in kilograms divided by the square of height in meters.
Measurements of Lipids and Apolipoproteins
A venous blood sample was drawn from an antecubital vein in all subjects after overnight fasting. The levels of total cholesterol (TC) and TG in serum samples were measured by an enzymatic technique (RANDOX Laboratories Ltd., Ardmore, Diamond Road, Crumlin Co. Antrim, UK), and the concentrations of high-density lipoprotein cholesterol (HDL-C) and LDL-C were detected with one-step enzyme immunoassay (Daiichi Pure Chemicals Co., Ltd., Tokyo, Japan). Serum apo A-I and apo B levels were measured by an immunoturbidimetric assay (RANDOX Laboratories Ltd.). All determinations were performed with an autoanalyzer (Type 7170A, Hitachi Ltd., Tokyo, Japan) at the Clinical Science Experiment Center, the First Affiliated Hospital, Guangxi Medical University.
Diagnostic Standard
The normal values of serum TC, TG, HDL-C, LDL-C, apo A-I, and apo B levels and the ratio of apo A-I to apo B in our clinical science experiment center were 3.10 to 5.17, 0.56 to 1.70, 0.91 to 1.81, 1.70 to 3.20 mmol/L, 1.00 to 1.76, 0.63 to 1.14 g/L, and 1.00 to 2.50, respectively. Individuals with TC > 5.17 mmol/L and/or TG > 1.70 mmol/L were defined as hyperlipidemic.21Hypertension was defined as a systolic pressure of 140 mm Hg or higher and a diastolic pressure of 90 mm Hg or higher.22Subjects with a BMI ≤ 24 kg/m2 were diagnosed as overweight and subjects with a BMI > 28 kg/m2 as obese.23
Statistical Analyses
The measurement data are presented as mean ± standard deviation. The difference of two parameters was tested by Student's unpaired t-test. One-way analysis of variance was performed to assess the differences of ≥ 3 parameters. Significant differences were then subjected to multiple comparisons using the Newman-Keuls test. Enumeration data are expressed as percentages. The difference in percentages was tested using the chi-square test. To evaluate the associations between hyperlipidemia and gender (female = 0; male = 1); age (40-49 years = 1; 50-59 years = 2; 60-69 years = 3; 70-79 years = 4; ≥ 80 = 5); BMI (≤ 24 = 0; > 24 = 1), blood pressure (normotensive = 0; hypertensive = 1); alcohol consumption (nondrinking = 0; < 250 g wine per day = 1; 250-499 g/d = 2; ≥ 500 g/d = 3); cigarette smoking (nonsmokers = 0; < 10 cigarettes/day = 1; 10-19 cigarettes/day = 2; 20-39 cigarettes/day = 3; ≥ 40 cigarettes/day = 4); and nationality (Hei Yi Zhuang = 0; Han = 1), unconditional multiple logistic regression analysis was also performed in a combined population of Hei Yi Zhuang and Han, Hei Yi Zhuang, and Han. A p value of less than .05 was considered significant.
RESULTS
Demographic Characteristics, Health-Related Behaviors, and Lifestyle Factors
The demographic characteristics, health-related behaviors, and lifestyle factors of the Hei Yi Zhuang and Han populations are shown in Table 1. Systolic blood pressure, pulse pressure, prevalence of hypertension, and intakes of carbohydrate and salt in the Hei Yi Zhuang were significantly higher than those in the Han (p < .01 to .001), whereas the education level, waist circumference, body weight, BMI, and intakes of total energy, total fat, protein, and dietary cholesterol in the Han were significantly higher than those in the Hei Yi Zhuang (p < .001 for all). There were no significant differences in physical activity level, body height, diastolic blood pressure, alcohol consumption, cigarette smoking, and age and sex constituent ratio between the two ethnic groups (p > .05).
Lipid Levels and Prevalence of Hyperlipidemia
The increased rates of isolated TC and TG, and TC plus TG in the Hei Yi Zhuang and Han were 23.0% (151/657) versus 25.6% (133 of 520; p > .05), 7.3% (48 of 657) versus 6.5% (34 of 520; p > .05), and 5.9% (39 of 657) versus 10.2% (53 of 520; p < .01), respectively. Thus, the prevalence rates of hypercholesterolemia, hypertriglyceridemia, and hyperlipidemia in the Hei Yi Zhuang and Han were 28.9% (190 of 657) versus 35.8% (186 of 520; p < .05), 13.2% (87 of 657) versus 16.7 (87 of 520; p > .05), and 36.2% (238 of 657) versus 42.3% (220 of 520; p < .05), respectively (Table 2). The levels of TC, TG, LDL-C, and apo B in the Hei Yi Zhuang were also significantly lower than those in the Han (p < .05 to .001), but the levels of HDL-C and the ratio of apo A-I to apo B in the Hei Yi Zhuang were significantly higher than those in the Han (p < .01 and .001, respectively). There were no significant differences in the apo A-I levels between the Hei Yi Zhuang and the Han (p > .05). The effects of gender, BMI, hypertension, alcohol consumption, cigarette smoking, and age on serum lipid levels in the Hei Yi Zhuang and Han are shown in Table 3.
Risk Factors of Hyperlipidemia
The results of multiple regression analyses of associations between the prevalence of hyperlipidemia and lifestyle variables are presented in Table 4. The prevalence of hyperlipidemia was positively correlated with age, BMI, blood pressure, and nationality (Han; p < .05 to .001) and negatively associated with gender (female higher; P < .05) in the combined population of Hei Yi Zhuang and Han; positively associated with BMI and blood pressure in the Hei Yi Zhuang (p < .01 and < .05, respectively); and positively correlated with age, BMI, and blood pressure (p < .05 for all) and negatively associated with gender (female higher; p < .05) in the Han.
Lipid Levels in Different Villages
There were significant differences in TC, HDL-C, LDL-C, and apo B levels and the ratio of apo A-I to apo B in seven villages of the Hei Yi Zhuang (P < .05 to .001) and significant differences in the TG, HDL-C, and apo A-I levels and the ratio of apo A-I to apo B in nine villages of the Han (p < .05 to .001; Table 5).
DISCUSSION
The current study reveals that there are significant differences in the lipid profile, the prevalence of hyperlipidemia, and its risk factors for the middle-aged and elderly between the Hei Yi Zhuang and the Han, which might result from different dietary constituents,9,10socioeconomic milieu,24and hereditary background.15,16Although the Hei Yi Zhuang and Han live in the same district, the risk factors, as mentioned above, might be different. The great majority of the Hei Yi Zhuang population lives in mountainous areas. Corn is the staple food all year round. On ordinary days, they are vegetarian. By contrast, the Han population living in the same region takes rice as the staple food. The standard of living and the intake of animal fat are higher in the Han than in the Hei Yi Zhuang, and the body weight and BMI are also significantly higher than those in the Hei Yi Zhuang. A number of observations have demonstrated that a high intake of calorie, saturated fat, or dietary cholesterol can raise serum lipid levels because of the resultant increase in the synthesis of cholesterol in the liver.9,10In addition, the other main cause of difference in the lipid levels between the Hei Yi Zhuang and the Han may relate to the excessive intake of corn. Corn contains abundant dietary fiber and high-quality plant protein.25An association between dietary fiber intake and favorable lipid status has been reported in free-living men.26Dietary fiber can combine with cholesterol in food and decrease its absorption. In addition, it can reduce the absorption of bile acids, decreasing their enterohepatic circulation. Plant protein might raise the serum levels of HDL-C and promote the transportation and excretion of free cholesterol.25Corn oil is a kind of edible oil that is enriched with polyunsaturated fatty acid and monounsaturated fatty acid27and is mostly used for cooking by the Hei Yi Zhuang. A great deal of research has indicated that suitable intakes of polyunsaturated fatty acid and monounsaturated fatty acid can lower the serum levels of cholesterol and LDL-C.27,28Maize oil could increase the ratio of HDL-C to TC and decrease the ratio of LDL-C to HDL-C.27
It is generally accepted that androgens induce disadvantageous changes in lipid profile, whereas estrogens are held to have the opposite effect.29,30In the present study, we showed that the levels of TC, LDL-C, and apo B in the Hei Yi Zhuang were higher in females than in males and the levels of LDL-C and apo B in the Han were higher in females than in males. The prevalence of hyperlipidemia in the Han females is significantly higher than that in the males. This observation is similar to the finding from another study.31By contrast, there is no significant difference in the prevalence of hyperlipidemia between Hei Yi Zhuang males and females. This finding is somewhat different from that of several previous studies.17,18The reason for this discrepancy is unclear.
Currently available evidence indicates that lipid levels are closely related with age.32,33In the present study, the levels of HDL-C, LDL-C, apo A-I, and apo B and the ratio of apo A-I to apo B increase progressively with age in the Hei Yi Zhuang and the levels of TC, LDL-C, and apo B increase progressively with age in the Han. The prevalence of hyperlipidemia is positively correlated with age in the Han but not in the Hei Yi Zhuang. The difference between these two ethnic groups is not well understood. The increased prevalence of hyperlipidemia with increasing age in the Han might reflect inherent genetic factors.
Obesity is a major public health problem in Western civilizations and is becoming more prevalent in developing countries. The link between obesity and dyslipidemia has been clearly documented.34,35Obesity not only increases the prevalence of hyperlipidemia but also associates directly with diabetes, high blood pressure, and coronary artery disease. The current study shows that the levels of TG, LDL-C, and apo B in the Hei Yi Zhuang were higher in subjects with a BMI ≤ 24 kg/m2 than those with a BMI ≤ 24 kg/m2 and the levels of TC, TG, LDL-C, and apo B in the Han were higher in participants with a BMI > 24 kg/m2 than those with a BMI ≤ 24 kg/m2. The prevalence of hyperlipidemia is also positively correlated with BMI in both the Hei Yi Zhuang and the Han. This is in agreement with previous studies.34-36Dyslipidemia in obesity may result from insulin resistance.37,38The liver is an important target organ of insulin effects. Insulin resistance can decrease the repression of insulin on the concentrations of plasma free fatty acids, increase the plasma levels of free fatty acids, promote free fatty acids into the liver, and stimulate the synthesis and release of very low-density lipoprotein (VLDL) in the liver. At the same time, insulin resistance can also decrease the activity of lipoprotein lipase, reducing the metabolism of VLDL and increasing the levels of plasma VLDL.
The association between serum lipids and blood pressure is not well known. Studies have shown that the levels of TG, VLDL cholesterol, and apo E were significantly higher and the levels of apo A-I, apo A-II, and apo C-II were significantly lower in untreated hypertensive subjects than those in controls.39TC and non-HDL cholesterol levels increased significantly with increasing systolic or diastolic blood pressure in both sexes.40Some authors thought that this relationship might be a kind of random phenomenon.41But our study reveals that there were significant differences in the HDL-C and apo A-I levels between hypertensive and normotensive Hei Yi Zhuang subjects and TC and TG levels between hypertensive and normotensive Han subjects. The prevalence of hyperlipidemia is also positively correlated with blood pressure in both the Hei Yi Zhuang and the Han. Our conjecture is that there might be a biologic interrelationship between blood pressure and lipids.42
Earlier studies have proved that high alcohol intake43,44and cigarette smoking11,12have a disadvantageous effect on lipid profiles. In the present study, although we show that there are significant differences in the HDL-C, LDL-C, apo A-I, and apo B levels between Hei Yi Zhuang nondrinkers and drinkers and the HDL-C, LDL-C, and apo A-I levels and the ratio of apo A-I to apo B between Han nondrinkers and drinkers and the TC, LDL-C, and apo B levels between Hei Yi Zhuang nonsmokers and smokers and the TC, LDL-C, and apo B levels and the ratio of apo A-I to apo B between Han nonsmokers and smokers, there is no significant correlation between the prevalence of hyperlipidemia and alcohol consumption or cigarette smoking in both the Hei Yi Zhuang and the Han, suggesting that both alcohol consumption and cigarette smoking may not be the independent risk factors for hyperlipidemia in these populations.
In the present study, we also showed that there are significant differences in the lipid levels in different villages of the Hei Yi Zhuang or Han. The reason for this difference among the villages is not yet known.
CONCLUSION
The current observation shows that there are significant differences in the lipid profile, the prevalence of hyperlipidemia, and its risk factors for the middle-aged and elderly between the Hei Yi Zhuang and the Han. The prevalence of hyperlipidemia is positively correlated with BMI and blood pressure in the Hei Yi Zhuang, whereas it is positively associated with age, BMI, and blood pressure and negatively associated with gender (female higher) in the Han. These differences might result from the effects of different demographic characteristics, health-related behaviors, and lifestyle factors.