The present study provided up-to-date prevalence of CVD and its major risk factors among rural adults aged above 40 in Beijing. As one of the strengths, a large community-based stable population was recruited, and the elderly beyond 85 years, who were ignored by most studies, were also included for its highest CVD incidence rate. Furthermore, to enhance the comparability with previous studies, age- and sex-standardized data based on both China population 2000 and 2005 were also provided. In addition, standard protocols and instruments were used, and strict training and a vigorous quality assurance program were conducted to ensure that high-quality data were collected for this study.
The main results of this study demonstrated highly prevalent CHD and stroke in rural areas around a large and fast developing city. Despite lack of data on CHD prevalence, there were several prevalence reports on stroke available for comparison. Previous nationwide studies in China had given a stroke prevalence rate of 0.53% for people aged over 45 years in the 1980s, with higher prevalence in northern cities, such as Beijing, than in the south [15
]. However, at the very beginning of this century, from National Nutrition and Health Survey, an standardized stroke prevalence of 1.11% (1.26% in male versus 0.96% in female, 1.47% in the north versus 0.72% in the south, and 1.54% in urban versus 0.76% in rural) was reported in general Chinese population aged over 35 years in 2002 [17
], which, in spite of being conducted in a relatively younger population, showed an obviously increased stroke prevalence in the past two decades. To add more evidence to the increased trends of CVD, our study provided recent stroke prevalence overall (3.7%), in male (4.7%) and in female (2.6%), which were higher than results of previous studies above, and CHD prevalence (5.6% overall, 5.2% in male and 5.9% in female) in a rural population aged beyond 40 living in North China. CHD and stroke prevalence in China are to some extent indicated to be in trends of rising, and are probably more prominent in northern area. More important, the rural areas around big cities might have been overwhelmed by CVD burden.
Furthermore, a probably changed pattern of CVD prevalence in rural Chinese was presented by the current study. Compared to Western populations, stroke was used to be regarded more common than CHD in Chinese population, especially for rural residents [18
]. This impression mostly stemmed from the much higher incidence and mortality of stroke than that of CHD based on the Sino-MONICA project conducted from 1987 to 1993, which was one part of WHO MONICA (World Health Organization's Monitoring Trends and Determination in Cardiovascular Disease) project [20
]. In the Sino-MONICA project, 7 years surveillance in Beijing indicated incidence and mortality from stroke were 3 times and 1.5 times those of CHD, which would have led to more people with stroke be accumulated than those with CHD, so that higher stroke prevalence would have been observed nowadays. Nevertheless, our study indicated a result of higher CHD prevalence (5.6%) than stroke prevalence (3.7%) recently, which might change the previous knowledge about pattern of CVD in China. Despite lack of comparable data in China and other Asian countries, studies in Japan added evidence to increased incidence and declined mortality for CHD and also declined incidence of stroke in both urban and rural Japanese communities [21
]. Considering incidence and mortality as two critical factors of prevalence rate, these evidences above suggested a distinctive transition that much heavier burden of CHD might have already existed in Asian countries with a CVD pattern similar to Western countries.
To further describe the CVD epidemic pattern in rural Beijing, data for prevalence of its major risk factors, including diabetes, hypertension and overweight/obesity, were also collected in our study. Hypertension, as an important risk factor of CVD, was found to be highly prevalent among adults in Fangshan District, with much higher prevalence than results from the 2000-2001 InterASIA study [8
]. Moreover, a set of increased odds ratios for different blood pressure categories from prehypertension to stage 2 hypertension were also shown to be associated with CHD/stroke, which suggested people with higher blood pressure would be at more risk. In addition, the differences of odds ratios for CHD and stroke indicated a closer relationship between hypertension and stroke, which supported the notion from the INTERSTROKE study published recently [23
]. Thus, the prevalent hypertension might contribute to explain relatively high stroke prevalence in rural Chinese. Besides hypertension, diabetes and obesity are also important risk factors of CVD. Although diabetes prevalence in our study was lower than the 2007-2008 China National Diabetes and Metabolic Disorders Study (9.7% in total, 10.6% in males and 8.8% in females) [24
], its actual prevalence in Fangshan District might be higher, due to lower awareness of diabetes in rural population in China [25
]. The prevalence of overweight and obesity in this study were much higher than national level in 2000-2001 [7
]; however, together with other previous evidence [26
], this transition reflected the strikingly increase of obesity and might lead to prevalent CHD in China subsequently. Furthermore, prevalence of CVD risk factors in our study was also higher than their counterpart in suburban of Beijing, from a cross-sectional survey in 2007 [5
]. Through this comparison, CVD risk factors were found to be more common in rural Beijing, and the remarkable overweight/obesity prevalence probably has a close relationship with nutritional transition in Chinese as previous study indicated [27
Although it is not the main focus of the study and lack of data from similar researches to compare with, an interesting finding is the diversity in the distribution of CVD and its risk factors across three different geographic areas. Diabetes, hypertension, overweight and obesity prevalence were illustrated to be lower in mountainous area compared with either hilly or plain area, which seemed to be a contradiction with the higher prevalence of CHD and stroke there. It may highlight the importance of other risk factors which were temporarily not explored in our study, such as smoking, family history and lipid profiles. Moreover, it probably also attribute to the inconvenient transportation and low socio-economic status in mountainous area: on the one hand, many labors free of diseases moved from mountainous to plain area, while the sick stayed at home; on the other hand, the poorer medical condition and education level in mountainous area led to the lower awareness of CVD risk factors. Hence lower awareness, treatment and control of CVD risk factors in mountainous area would possibly aggravate the CHD/stroke epidemic.
Besides the major risk factors described above, population aging might be another important force driving the increase of CVD prevalence. It was forecasted that CHD incidences and deaths in China would increase dramatically over 2010-2029, due to population growing and aging alone [28
]. Furthermore, the elder population is usually suffering much higher CVD prevalence. Although few data on CHD prevalence for the elders was published so far, there were still a few reliable stroke reports. In some developed countries, the stroke prevalence for people aged 65 years and above ranged from 4.61% to 7.33% (directly standardized to the Segi 1996 world population) [29
]. During 2005 national survey in the United States, 8.1% of persons aged 65 years and above reported they had had a history of stroke, whereas the proportion in population aged 45-64 years is 2.7% [30
]. In Asia, recent study also pointed out a high prevalence of 10.2% for stroke in residents older than 65 in Korea (directly standardized to the 2005 Korean population) [31
]. To make complements, our study provided standardized prevalence of 10.9% for CHD and 6.9% for stroke among participants 65 years and above, much higher than 4.1% for CHD and 2.8% for stroke among individuals below 65 years (directly standardized to the adult sample data of 2000 China 5th
Population Census); and this disparity was even greater in female. Moreover, a higher prevalence of CHD in females aged 65 and above than males was presented in our results, which was inversed from corresponding data of stroke and probably seemed to be contrary to the common ideas; however an earlier population-based study conducted in Hong Kong also reported a much higher CHD prevalence of 9.7% in Chinese women aged 65-74 years than men (5.1%) [32
], which was consistent with our study. World population is aging and this has already made a considerable impact on the CVD burden in developed countries in recent decades. It is reasonable to suppose that, as the age structure of the Chinese population increases, the CVD burden in China will be aggravated and might be different by genders.
Urbanization should also be considered as a rational reason to explain higher prevalence of CVD and its risk factors in rural population [24
]. Though China has the largest population in developing countries with an unbalanced development throughout the whole country, the westernization of lifestyles is accelerated not only among urban residents but also among rural population, especially for the ones nearby modern region [33
]. Fangshan District is a typical rural area in the southwest of Beijing, one of the most modernized cities in China, and it might probably be suffered by a high burden of CVD. Thus, taken in this sense, our results may have further public health implications.
Several limitations in our study should be addressed. Firstly, it was a cross-sectional study which could not tell the true relationship between cardiovascular risk factors and CVD. However, it has already been demonstrated in Chinese adults by previous studies [34
]. Secondly, twice as many women as men were investigated, probably because part of young and male labor force that went to work in big cities was unavailable for this survey, which is a common problem in rural China. Thirdly, estimation of CHD and stroke prevalence was mainly based on record-verified self-reported data. On the one hand, local general practitioners, who were familiar with health issues of their patients in the serving communities, participated in the investigation to decrease under-reporting level; on the other hand, in order to avoid over-reporting, qualified cardiologists and neurologists were also joined to confirm the diagnosis of diseases through medical record review. Finally, relatively limited information was collected for this large population in the initial baseline, but more detailed information such as surveillance data, life-style risk factors and lipid profiles were scheduled to be added in the next stage as well, so the findings in this study may provide clues for further investigations.