Prevalence and Related Factors of Dyslipidemia among Adults Aged 35 to 79 years in Southwest China

This study aimed to investigate the prevalence of dyslipidemia and its related factors among adults aged 35 to 79 years in southwest China. From September 2013 to March 2014, a multi-stage, stratied sampling was conducted on 10221 people aged 35–79 years living in Chengdu and Chongqing by using the method of eld questionnaire survey and measurement. The prevalence of high triglycerides ( ≥ 2.3 mmol/L), high total cholesterol ( ≥ 6.2 mmol/L), high low-density lipoprotein cholesterol ( ≥ 4.1 mmol/L), low high-density lipoprotein cholesterol (< 1.0 mmol/L), and dyslipidemia were 15.7%, 5.4%, 2.5%, 5.7%, and 27.4%, respectively. The prevalence of dyslipidemia was positively correlated with higher education level, monthly income over 2000 yuan, smoking, hypertension, diabetes, overweight and obesity, and central obesity, and negatively correlated with daily physical exercise. The prevalence of dyslipidemia in southwest China is lower than the national average level, but on the rise, with high triglycerides as the main type of dyslipidemia. Trend analysis was done by Chi-Square trend test linear regression Both univariate multivariate were performed using an unconditional Logistic regression model, and the value and its 95% condence interval were calculated. All statistical analyses were performed with SPSS 23.0 software, and P < 0.05 was considered statistically signicant.


Introduction
Arteriosclerotic cardiovascular disease(ASCVD)is the leading cause of death in both developed countries 1,2 and most developing countries, including China 3 .The 2007 overall death rate 2 from CVD was 251.2 per 100 000. Dyslipidemia is one of the most important risk factors for ASCVD 4 , leading to atherosclerosis 5 , increased morbidity, and mortality from coronary heart disease 6 and ischemic stroke 7 .In recent years, with the rapid growth of the social economy, the prevalence of dyslipidemia in Chinese adults has been increasing gradually 6,8,9,10 . As representatives of southwest China, Chengdu and Chongqing, with the title of Chengdu-Chongqing economic circle, have also been faced with rapid economic development in recent years. However, there have been almost no epidemiological investigations related to dyslipidemia in southwest China. We, therefore, conducted this cross-sectional survey to provide advice on dyslipidemia management.

Demographic and clinical characteristics of the study participants
The basic characteristics of this study are shown in Table 1. Among the 10,221 respondents, 3,474 were men and 6,747 were women. The mean age was 55.0 ± 10.7 years, and the mean age of men was higher than that of women. Men have higher rates of monthly income over 2000 yuan, smoking, drinking, and daily exercise. The 2 h blood glucose, triglycerides, TC, HDL-C, and LDL-C levels were lower in men, and there was no signi cant difference in fasting blood glucose levels. Men had higher WC, SBP, DBP levels, and lower BMI levels. The prevalence of hypertension in men was slightly higher than that in women, and there was no signi cant difference in the prevalence of diabetes. Sex-and age-speci c mean of dyslipidemia Table 2 shows the lipid levels of different genders and ages. In men, triglyceride levels showed a downward trend with age, while LDL-C and HDL-C levels showed an upward trend, with no signi cant change in TC levels. In women, triglycerides, TC, and LDL-C levels showed an upward trend, while HDL-C levels showed no signi cant trend. Prevalence of dyslipidemia by selected characteristics Table 3 shows the relationship between different factors and the prevalence of dyslipidemia. The prevalence rates of high TG, high TC, high LDL-C, low HDL-C, and dyslipidemia were 15.7%, 5.4%, 2.5%, 5.7%, and 27.4%, respectively. The prevalence of dyslipidemia increased with age, and the prevalence of dyslipidemia was higher in men (30.2%) than in women (25.9%). Elevated TG was related to daily exercise, hypertension, diabetes, overweight, and central obesity. TC increased with age, gender, marital status, education level, smoking status, high blood pressure, diabetes, overweight, and central obesity.
Elevated LDL-C was associated with age and diabetes. Lower HDL-C was associated with gender, education level, income, smoking status, high blood pressure, overweight, and central obesity.
Dyslipidemia was associated with age, sex, education, monthly income, smoking status, daily exercise, hypertension, diabetes, overweight, and central obesity. Multivariable-adjusted ORs and 95%CI for dyslipidemia In Table 4, through multivariate logistic regression analysis, we found that the relationship between each factor and the prevalence of different types of dyslipidemia was as following. High TG was positively correlated with high school education, smoking, hypertension, diabetes, overweight and obesity, central obesity, but negatively correlated with daily physical exercise. Compared with 35-44 years old, TG elevation was higher in 45-54 years old but lower in 65-79 years old. For high TC, there was a positive correlation with diabetes, and a negative correlation was found for women with high school education or above. Compared with 35-44 years old, 65-79 years old group had a higher incidence of TC elevation. Elevated LDL-C was positively correlated with age and diabetes. Decreased HDL-C was positively correlated with female, high school education, monthly income over 2000 yuan, smoking, overweight and obesity, and central obesity but negatively correlated with age (35-44 years of age as a reference).
Dyslipidemia was positively correlated with high school education, monthly income over 2000 yuan, smoking, hypertension, diabetes, overweight and obesity, central obesity, but negatively correlated with daily physical exercise.

Discussion
This study investigated hyperlipidemia and related risk factors in urban adults aged 35-79 years in Chengdu and Chongqing from September 2013 to March 2014, based on a population in southwest China. In general, the average prevalence of dyslipidemia was 27.4%, which increased with age, and the prevalence of dyslipidemia was higher in men (30.2%) than in women (25.9%). The higher prevalence rate in men may be related to the higher income, smoking rate, drinking rate, WC, hypertension prevalence rate, SBP, and DBP level. But interestingly, the prevalence in women was lower than that in men under the age of 55, and it was higher in women later in life than in men. Moreover, with the increase of age, TG, TC, and LDL-C levels in women showed a signi cant increasing trend. This result was consistent with other studies 9,12 . This may be related to differences in estrogen levels in women before and after menopause 12 . However, in Table 4, multivariable analysis showed that dyslipidemia was unrelated to age and gender. This may be due to controlling for other factors, including mediators, to block the effect of age and sex on dyslipidemia. At the same time, we found that the prevalence rates of high TG, high TC, low HDL-C, and high LDL-C in people aged 35-79 years in southwest China were 15.7%, 5.4%, 5.7%, and 2.5%, respectively, while the prevalence rates of high TG, high TC, low HDL-C and high LDL-C in Chinese adults 9 were 12.17%, 7.50%, 15.31%, and 7.96%, respectively. Therefore, high TG was the main type of dyslipidemia in southwest China. The prevalence of high LDL-C was much lower in southwest China. Previous studies have shown that the LDL-C level is the indicator most closely related to ASCVD risk 19,20 . One research 21 analyzed data of 219,522 Chinese patients with type 2 diabetes and found that there were large regional variations in the prevalences and risks of coronary heart disease and stroke in T2DM in China. Southwest China had the lowest prevalence of both CHD and stroke in Chinese adults with type 2 diabetes. Another nationally representative survey 22 included 480687 adults aged ≥ 20 years demonstrated the lower prevalence of stroke in Southwest China. Despite its large population and high GDP, Southwest China had a low-ranking number of percutaneous coronary intervention 23 . Interestingly, contemporaneous studies 24,25 showed that the prevalence of hypertension(38.4%) and diabetes 19.5% in the Southwest was no lower than the national average hypertension 32.5% 26 ,diabetes 9.7% 27 . Therefore, it is reasonable to speculate that the low prevalence of dyslipidemia and low LDL-C contribute to the lower ASCVD prevalence in southwest China. However, due to the diversity of ASCVD risk factors and the limitations of cross-sectional studies, further studies should be expected.
This study also analyzed the correlation between dyslipidemia and various factors. In addition to the common risk factors associated with dyslipidemia 10,24 , such as smoking, hypertension, and diabetes, this study also showed a positive correlation between a high school degree or above, a monthly income of more than 2000 yuan, and the prevalence of dyslipidemia. This may be due to the better economic and nutritional status of people with higher education and income 25 . Overweight, obesity and central obesity are correlated with dyslipidemia, suggesting that BMI and waist circumference can be used as screening indicators for dyslipidemia, and weight control is an important prevention and control method 26,27 .
Besides, dyslipidemia was negatively correlated with daily physical exercise, suggesting that strengthening physical exercise is also an important method for the prevention and control of dyslipidemia.
In conclusion, our study provides the latest and reliable information for dyslipidemia in southwest China.
The results show that the prevalence of dyslipidemia in southwest China was lower than the national average but on the rise. High TG was the main type of dyslipidemia, and the prevention and control of dyslipidemia are faced with challenges. Dyslipidemia is closely related to smoking, hypertension, diabetes, higher education, higher income, obesity, and central obesity. Only by strengthening public health education and intervening in risk factors can we face the challenge.

Study population
From September 2013 to March 2014, a multi-stage, strati ed sampling was conducted on 13378 people aged 35-79 years living in Chengdu and Chongqing by using the method of eld questionnaire survey and measurement. In the rst stage of this study, Jinjiang, Longquanyi, and Chenghua districts were randomly selected in Chengdu urban area, and Yubei district and Jiangbei district were randomly selected in Chongqing urban area. In the second stage, a street is randomly selected from each major area; in the third stage, a community is randomly selected from each street to form a sample composed of ve random communities. The ethics committee of the Second People's Hospital of Chengdu approved this study protocol (NO 2013015). All participants provided written informed consent.

Inclusion and exclusion criteria
From September 2013 to March 2014, residents aged 35 to 79 years who had lived in selected communities for more than ve years were included in the study. People with secondary hypertension, mental illness, malignancy, renal failure requiring dialysis, or refusal to participate were excluded. Due to the lack of demographic information and weight, blood pressure, waist circumference, or body mass index (BMI) data, and lipid measurements, 10,221 participants were included in the nal analysis.

Data collection
More than 30 investigators were trained in data collection. According to the cardiovascular survey methodology developed by the World Health Organization 11 , subjects lled out the same eld questionnaire, including demographic characteristics; lifestyle, personal and family history of the disease; measurements of height, weight, waist circumference, and blood pressure; fasting glucose, triglycerides (TG) and total cholesterol (TC) levels were also included. BMI was calculated by dividing weight in kilograms by height in meters squared, and subjects were asked to go barefoot and wear only light clothing when measuring height and weight. The researchers measured the minimum circumference between the lower edge of the rib and the iliac spine to get a waist measurement. Thirty minutes before the measurement of blood pressure, the subjects were told not to drink coffee, tea, or alcohol, and not to smoke or exercise. The subjects sat for a ve-minute break, then had their blood pressure measured while they sat with a mercury sphygmomanometer. Systolic blood pressure (SBP) and diastolic blood pressure (DBP) recorded the rst occurrence of Korotkoff sound (stage I) and the disappearance of Korotkoff sound (stage V), respectively, and averaged the blood pressure readings of the two measurements. All anthropometric measurements and blood biomarkers testing were carried out in accordance with relevant guidelines and regulations.

Index de nition
Smoking now is de ned as having smoked more than 100 cigarettes in a lifetime. Drinking is de ned as consuming more than 30 grams of alcohol per week for more than a year. Regular physical activity refers to moderate or vigorous activity of 30 minutes or more on at least 3 days a week 8 . Hypertension is de ned as having a clear medical history, and/or systolic blood pressure greater than or equal to 140 mmHg, and/or diastolic blood pressure greater than or equal to 90 mmHg. Diabetes is de ned as having a clear medical history, and/or fasting glucose greater than or equal to 7.0 mmol/L, and/or a 2hour glucose tolerance test greater than or equal to 11.1 mmol/L. According to the guidelines for

Statistical analysis
Absolute number (percentage, %) was used to describe the categorical data, and a Chi-Square test was used to compare the difference between different groups. The data subject to or close to the normal distribution were described by means + standard deviation, and the difference between different groups was compared by Student's t-test. The data of skewed distribution were described by the median with the interquartile range, and the comparison between different groups was performed by Wilcoxon rank sum test. Trend analysis was done by Chi-Square trend test or linear regression analysis. Both univariate and multivariate analyses were performed using an unconditional Logistic regression model, and the OR value and its 95% con dence interval were calculated. All statistical analyses were performed with SPSS 23.0 software, and P < 0.05 was considered statistically signi cant.

Competing interests
The authors declare no competing interests. Figure 1 Age-speci c prevalence of high triglyceride, high total cholesterol, high low-density lipoprotein cholesterol, low high-density lipoprotein cholesterol, and dyslipidemia among the adults aged ≥ 35 years in southwest China