Liu et al. BMC Public Health 2011, 11:931 http://www.biomedcentral.com/1471-2458/11/931 threshold down to at least 115/75 mmHg [30]. Mass population interventions that use dietary, lifestyle, or environmental factors to move blood pressure distribu- tion downwards has the potential to produce large reduc- tions in the burden of cardiovascular disease in China [31]. A reduction in the average DBP of just 3 mmHg would avert approximately one-third of stroke deaths in China, where stroke is more common than coronary heart disease [32]. In addition, data showed that there is no threshold below which a lower TC concentration (e.g., below 154 mg/dl, 4 mmol/l) is not associated with a lower risk of ischemic heart disease [33]. The sharp increase in serum lipids observed among workers and farmers is alarming. Data from Eastern Europe suggested that cholesterol level responded rapidly to changes in lifestyle and diet, and that mortality increased relatively quickly after the cholesterol increases [34]. In addition, the absolute excess risks for higher BMI and smoking were additive [35]. Induction periods from exposure to a risk factor to a disease occurrence may be shorter when other causal factors are common [36]. In Guangzhou, smoking was already very prevalent (in men) before blood pressure and cholesterol levels increased. There- fore, a sharp increase in prevalence, incidence, and mor- tality of cardiovascular disease can be predicted. This study has several limitations. The participants were recruited from cluster samples from one factory and one rural area and were aged 25-64 years at base- line. They were not the representative samples of the general populations. In addition, there was a potential healthy worker effect of the cohorts. The follow-up examinations were not performed after 1994. China has seen remarkable economic growth over the past 30 years. It is expected that large changes in risk factor levels continued beyond 1994 that were not captured in this report. Conclusions This cohort study of low risk workers and farmers in south China indicates unfavorable trends of cardiovascu- lar risk factors from 1983-1994. Increase in BMI was significantly associated with increase in blood pressure and TC levels. The unfavorable trends persisted after adjusting for aging of the cohort, education, BMI, smok- ing, and alcohol intake. The adverse changes in risk fac- tor levels mirrored the dramatic economic and environment changes in the society. Thus, in addition to changes in the behavior, attitudes, and social values of individuals, change to society, systems, and policies that promote major risk factors are crucial. Grass root pri- mordial prevention is important and urgently needed to preserve these so far low risk populations from the penetration of risk factors and disease epidemics [37]. Page 8 of 9 Acknowledgements This study was supported by the National Heart, Lung, and Blood Institute of the U.S. National Institute of Health, Chinese Ministry of Public Health, and by the Guangdong Provincial Cardiovascular Institute in Guangzhou, China. We appreciate the many colleagues who collected data of the cohorts over the years and acknowledge the important contribution of a number of U.S. scientists and the assistance of quality control from the U.S. CDC. We also thank Dr. Youlian Liao from CDC for his assistance in the data analysis and for carefully reviewing the manuscript. Authors’ contributions XL participated in the design of the study, data analysis, and drafted the manuscript. JM participated in data analysis, interpretation of data, and manuscript revision. XR participated in the conception and design of the study, initiated the data collection, and manuscript revision. QZ oversaw laboratory tests, quality control, and manuscript revision. CG, XG, YW, and MD assisted with data collection, study coordination, quality control, interpretation of the findings, and manuscript revision. SL conceived of the study, directed all stages of the study, participated in its design and coordination, and manuscript revision. All authors read and approved the final manuscript. Competing interests The authors declare that they have no competing interests. Received: 22 July 2011 Accepted: 14 December 2011 Published: 14 December 2011 References 1. Liu L: Cardiovascular diseases in China. Biochem Cell Biol 2007, 85:157-163. 2. Wu Z, Yao C, Zhao D, Wu G, Wang W, Liu J, Zeng Z, Wu Y: Sino-MONICA project: a collaborative study on trends and determinants in cardiovascular diseases in China, Part i: morbidity and mortality monitoring. Circulation 2001, 103:462-468. 3. Gu D, Reynolds K, Duan X, Xin X, Chen J, Wu X, Mo J, Whelton PK, He J: Prevalence of diabetes and impaired fasting glucose in the Chinese adult population: International Collaborative Study of Cardiovascular Disease in Asia (InterASIA). Diabetologia 2003, 46:1190-1198. 4. Reynolds K, Gu D, Muntner P, Wu X, Chen J, Huang G, Duan X, Whelton PK, He J: Geographic variations in the prevalence, awareness, treatment and control of hypertension in China. J Hypertens 2003, 21:1273-1281. 5. He J, Gu D, Reynolds K, Wu X, Muntner P, Zhao J, Chen J, Liu D, Mo J, Whelton PK: Serum total and lipoprotein cholesterol levels and awareness, treatment, and control of hypercholesterolemia in China. Circulation 2004, 110:405-411. 6. Wu Z, Yao C, Zhao D, Wu G, Wang W, Liu J, Zeng Z: Cardiovascular disease risk factor levels and their relations to CVD rates in China– results of Sino-MONICA project. Eur J Cardiovasc Prev Rehabil 2004, 11:275-283. 7. Wu X, Huang Z, Stamler J, Wu Y, Li Y, Folsom AR, Tao S, Rao X, Zhang H, Cen R, et al: Changes in average blood pressure and incidence of high blood pressure 1983-1984 to 1987-1988 in four population cohorts in the People’s Republic of China. The PRC-USA Cardiovascular and Cardiopulmonary Epidemiology Research Group. J Hypertens 1996, 14:1267-1274. 8. Critchley J, Liu J, Zhao D, Wei W, Capewell S: Explaining the increase in coronary heart disease mortality in Beijing between 1984 and 1999. Circulation 2004, 110:1236-1244. 9. Li YH, Li Y, Davis CE, Chen Z, Tao S, Folsom AR, Bachorik P, Stamler J, Abernathy JR: Serum cholesterol changes from 1983-1984 to 1993-1994 in the People’s Republic of China. Nutr Metab Cardiovasc Dis 2002, 12:118-126. 10. Folsom AR, Li Y, Rao X, Cen R, Zhang K, Liu X, He L, Irving S, Dennis BH: Body mass, fat distribution and cardiovascular risk factors in a lean population of south China. J Clin Epidemiol 1994, 47:173-181. 11. Wu YK, Lu CQ, Gao RC, Yu JS, Liu GC: Nation-wide hypertension screening in China during 1979-1980. Chin Med J (Engl) 1982, 95:101-108. 12. PRC National Blood Pressure Survey Cooperative Group: Prevalence and development trends of hypertension in China. Chinese J Hypertension 1995, 3:s7-s13.