Background
Obesity, a key cause of cardiovascular disease (CVD), is becoming a worldwide health concern [
1]. According to the Chinese resident’s chronic disease and nutrition report in 2015, obesity rates among those 18 years old and above in China were 11.9% in 2012, which indicates that there were more than 124 million obese adults in China in 2012 [
2]. Additionally, there were 292 million adults with hypertension in China in 2013–2014; in 2002, there were 153 million adults with hypertension [
3]. However, in 2013 in China, the overall blood pressure control rates of adults with hypertension was only 9.7% [
3]. Abnormally high blood pressure can lead serious health problem. In 2013, high systolic blood pressure caused 10.4 million deaths and 208.1 million disability-adjusted life years in the world [
4].
Previous studies have revealed that obesity seemed to increase the risk of hypertension. In China, body mass index (BMI) is usually used to assess obesity [
5]. However, obesity, as defined by BMI, is not a fitness indicator of body fat distribution [
6]. Central obesity, measured by waist circumference (WC), has been shown to be a strong risk factor for the prevalence of hypertension and stroke [
7]. Compared to individuals with a normal BMI, a population with central obesity has a higher risk of incident hypertension [
8]. Additionally, with the improvement of living standards, young Chinese generations are facing more serious obesity problems, and younger cohorts have a higher prevalence of obesity than older cohorts [
9,
10]. When these young people become older, those with central obesity will have a higher risk of developing hypertension later in life than those with general obesity [
11].
However, studies comparing the trend in the prevalence of different types of obesity and the association with hypertension in urban and rural areas in China are scarce. Most studies have focused only on the difference in the prevalence of overweight and general obesity or hypertension among rural and urban populations [
12,
13]. In recent decades, the economy of China has grown dramatically, leading to rapid urbanization in rural China. A previous study showed that China’s disease spectrum had significantly changed from communicable to noncommunicable diseases during China’s urbanization from 1995 to 2010 [
14], and chronic health conditions, such as overweight and hypertension, were associated with urbanization [
15]. Additional research is needed to explore the impact of urbanization in China on the prevalence of different types of obesity and the association with hypertension.
Therefore, this study focuses on examining the shifts in the overall distribution of the prevalence of different types of obesity and estimates the risk of hypertension with different types of obesity, while also comparing the discrepancy between urban and rural adults aged 18–65 years in China. We used cross-sectional data from a survey administered in China over 18 years to conduct our study.
Discussion
In our study, we demonstrated that the age-standardized prevalence of central obesity only, general obesity only, and both central and general obesity all increased significantly in Chinese adults from 1993 to 2011. The prevalence of participants with central obesity only was the highest for the three types of obesity. Additionally, the prevalence of central obesity only and both central and general obesity in adults in rural areas exceeded that of adults in urban areas in 2011. Participants with both central and general obesity had the highest risk of incident hypertension compared with those with normal BMIs and WCs.
This study showed that an upward trend was noted in the distribution of BMIs and WCs in Chinese adults aged 18–65 years. The mean BMI increased from 21.9 kg/m
2 to 24.0 kg/m
2, and the mean WC increased from 75.6 cm to 83.7 cm in 1993 and 2011, respectively. These results are in line with previous studies [
9‐
11]. Distribution curves of BMIs and WCs shifted to the right, which indicated that the population suffered a higher proportion of obesity and overweight. As we found, the prevalence of obesity, whether defined by BMI or WC, has increased significantly over the past 18 years in China, particularly central obesity. The rising trend is similar in Korean men, whose prevalence rate of abdominal obesity increased from 22.1% in 1998 to 27.5% in 2007 [
25]. In addition, in the three types of obesity, we revealed that the prevalence of central obesity with a normal or abnormal BMI (30.3 and 10.3% in 2011) was far higher than that of general obesity with a normal WC (0.9% in 2011), and no difference was found between participants from urban and rural areas. This constitution of different types of obesity has also been reported in a previous study, in which the constituent ratio of subjects with an exclusive BMI ≥ 28 kg/m
2 was only 0.9% in 2009 [
8]. This finding suggests that it may be more accurate to combine WC and BMI when screening for obesity.
One of the concerns in our study was whether there was a similarity or difference in the prevalence of obesity among adults in urban and rural areas in China. Notably, the prevalence of central obesity increased more quickly among adults in rural areas than among adults in urban areas in this study. This result seems to be consistent with previous studies that found that the prevalence of central obesity of residents in rural areas increased more rapidly than that of residents in urban areas [
8,
26]. However, we have some new findings. First, the gap between the prevalence of central obesity only and both central and general obesity between adults in urban and rural areas narrowed from 1993 to 2011. Second, the overall prevalence of central obesity in adults in rural areas was beyond that in adults in urban areas in 2011. These findings may be attributed to the changes in China’s social and economic structure led by China’s urbanization [
27]. A previous observation confirmed that chronic health conditions, such as overweight, are associated with modernization and affluence, and the appearance of these conditions is no longer restricted to urban populations [
15]. In China, the average food consumption per person in rural households increased from 890.3 Yuan in 1997 to 2323.9 Yuan in 2012, and the Engel coefficients of urban and rural households were 46.6 and 55.1% in 1997 and 36.2 and 39.3% in 2012, respectively [
28]. Along with urbanization, the food consumption capacity of adults in rural areas has developed rapidly. Therefore, it is possible that accelerated health decline, such as the prevalence of central obesity in more urbanized areas, is exacerbated by a high-fat diet and decreased physical activity [
29].
Another aim of our study was to estimate the risk of hypertension with the three types of obesity and to compare the differences between adults in urban and rural areas. The positive relationship between hypertension and obesity has been reported widely in many studies [
11,
30‐
33]. In Chinese adults, BMI is highly associated with high blood pressure [
32], and changes in BMI show a dose-response relationship with incident hypertension [
33]. WC provides a unique indicator of body fat distribution and has often been used as a reasonable predictor of the risk of hypertension [
34]. Previous studies have reported that central obesity also raises the risk of incident hypertension in later life [
11] and leads to a higher risk of incident hypertension compared with that of individuals with a normal BMI [
8]. However, studies have not investigated whether a population with central obesity has a higher risk of incident hypertension compared with a population with general obesity. Limited information from previous studies is available [
8]; however, our results expanded on this information. We found that the risk of hypertension among the three types of obesity in adults in urban areas is as follows: both central and general obesity > general obesity only > central obesity only and in adults in rural areas is both central and general obesity > central obesity only > general obesity only. This indicates that central obesity not only is an independent risk of hypertension but also increases the risk when accompanied by general obesity.
Several limitations exist in our study. First, as a limitation of the data, we cannot provide exact explanations for the prevalence of central obesity among adults in rural areas exceeding that of adults in urban areas in 2011. Second, the risk of hypertension with central obesity only and general obesity only is not consistent in adults in urban and rural areas. If central obesity is commonly used as a reasonable predictor of the risk of incident hypertension in Chinese adults, which should be consistent in urban and rural adults, future research may be needed to examine the reasons for this. Third, although our sample size was large and the participants were from eight provinces in China, the sample was still only a part of China, and a broader national study should be conducted to support the results. Fourth, the data of CHNS used in this study is cross-sectional data, the causal inference is weak, and it is difficult to deeply explore the relationship between obesity and hypertension. Fifth, the most recent data in our study was from 2011, but China’s urban and rural areas are still very much changing, and an updated study should continue to pay attention to and observe the difference in trends of residents of urban and rural areas in China.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.