Liu et al. BMC Public Health 2011, 11:931 http://www.biomedcentral.com/1471-2458/11/931 Guangzhou is a coastal city in the southeast corner of China. The people who live in Guangzhou are much lea- ner, with a body mass index (BMI) of around 20-21 kg/m2 [10]. The national surveys [11,12] conducted during 1980s and 1990s showed that the prevalence of hypertension in Guangdong province, where Guangzhou is located, was less than 10% in adults. The prevalence was among the lowest in the country and much lower than those among various populations in the Asia-Pacific region [13], or in the world [14] including sub-Saharan Africa [15]. In 1984, coronary heart disease mortality among those aged 35-74 years in Guangzhou was one-third of that in Beijing and one-tenth (men) to one-fifth (women) of those in North America and Australia [16]. Guangzhou has developed faster, and its economy has grown more quickly than most other areas in China since 1980s. The purpose of this study is to examine the 10-year trends of cardiovascular risks (1983-1994) and the factors related to these trends among the low-risk cohorts of workers and farmers in Guangzhou, China. Methods Study cohorts In 1981, a joint research program, the Collaborative Study of Cardiovascular and Cardiopulmonary Epidemiology, was initiated between the United State of American (USA) and the People’s Republic of China (PRC) under the USA- PRC Cooperation in Science and Technology [17]. Cohorts of Chinese populations were established from four sites: two in northern China (urban and rural Beijing) and two in southern China (urban and rural Guangzhou). The study protocol was developed jointly by the scientists from the U.S. and the PRC. Field investigators were trained and certified before the data collections. In urban Guangzhou, the participants were clustered samples from a factory–the Guangzhou Shipyard Com- pany. All persons, primarily manual labor workers, aged 25-64 years from 8 of the 25 workshops were recruited. The response rates were 84% and 91% for males and females, respectively. The rural participants were from Dashi Township of Panyu County, 20 km south of Guangzhou City. Of the 21 village clusters, 14 were sampled. All persons, primarily farmers, aged 25-64 years were recruited. The response rates were 91% and 94% among males and females, respectively. The study was approved by the Science and Ethics Committee of the Guangdong General Hospital, the executive office of Guangzhou Shipyard Company and the municipal office of Dashi Township. Baseline examinations were conducted for half of the cohort during 1983 and the other half during 1984. Fol- low-up re-examinations were conducted during 1987-1988 (4 years after baseline) and again during 1993-1994 (10 years after baseline). All examinations were performed Page 2 of 9 during September and October. At baseline, 3,437 workers and 3,629 farmers completed the questionnaire interviews and physical examinations. Among them, 3,131 workers (1,564 males and 1,567 females) and 3,493 farmers (1,521 males and 1,972 females) had at least one re-examination and were included in this analysis. Excluding 91 persons who died before the first re-examination, the retention of the surviving cohort was 92% for workers and 98% for farmers. Data collection Demographic, medical, behavioral, and lifestyle data were collected. Participants were asked if they ever attended school, graduated from primary school, middle school, high school, or college. In addition, the participant was asked if he or she was current smoker and the average number of cigarettes smoked per day. A small percentage of farmers were pipe smokers or smoked hand-made cigarettes. The equivalent number of cigarettes smoked per day was estimated by using the monthly consumption of tobacco leaves (about 1 g of tobacco per commercial cigarette). Daily alcohol intake was calculated by summing the intakes from various alcoholic beverages in the past week. The participants were asked to report the amount of drinking for each type of alcoholic beverage including beer, grape (or other fruits) wine, Huangjiu (“yellow wine” brewed from grains), rice wine, and liquor/spirit. The alco- hol content was 3.6% for beer, 12% for grape wine, 12% for Huangjiu, 26% for rice wine, and 47% for liquor/spirit. Body weight was measured by using a spring scale, with participants in light clothing without shoes. Height was measured by using a vertical ruler. BMI was calculated as weight in kilogram (kg) divided by height in squared meter (m2). Overweight was defined as having a BMI of 25 kg/m2 or higher and obesity was defined as BMI of 30 kg/m2 or higher. Three systolic (SBP) and fifth-phase diastolic blood pressures (DBP) measurements were taken on the right arm with a mercury sphygmomanometer and the average of the three readings was used in the analysis. Hypertension was defined as SBP ≥ 140 mmHg and/or DBP ≥ 90 mmHg or on antihypertensive medication. Participants were asked to fast for at least 12 h before blood samples were drawn. Some participants either did not fast for at least 12 h or they declined to have blood drawn. Baseline and at least one follow-up lipid mea- sures were performed in 2,118 workers (1,072 males and 1,046 females) and 2,241 farmers (1,059 males and 1,182 females). Blood lipids were measured and standardized according to the Lipid Standardization Program of the U.S. Centers for Disease Control and Prevention (CDC) and followed a quality control program using samples prepared by the CDC. The mean percentage biases based on means pooled TC measured, less CDC reference mean, was