Liu et al. BMC Public Health 2011, 11:931 http://www.biomedcentral.com/1471-2458/11/931 change in BMI was significantly and directly associated with change in LDL-C, triglycerides; and inversely asso- ciated with change in HDL-C. Additional analysis We repeated the analyses assuming that the mean TC were 2.2 mg/dl higher than they would have been had all the 1993-1994 measurements been made using fresh sera. The age-adjusted average 10-year increase in TC was 6.7 mg/dl for male workers, 20.6 mg/dl for male farmers, 0.8 mg/dl for female workers and 14.7 mg/dl for female farmers. The coefficients for follow-up time were statistically significant among all groups except female workers in GEE analyses. The relations between baseline measures of covariates and the average TC and between the changes in covariates and changes in TC were similar to those without correction for the individual TC values (data not shown). Discussion This cohort study of workers and farmers in southern China shows significant adverse trends of cardiovascular profiles in a 10 years period independent from the aging process of the cohorts. The results of this study confirm the rapid epidemiologic change underway in these popu- lations that used to have very low cardiovascular risk. Most of the studies evaluating changes in the levels of cardiovascular risk factors in the population were con- ducted through multiple cross-sectional observations on non-overlapping samples [6,8,19,20]. The limitation of such a design is that differential cohort effects in the dif- ferent cross-sectional samples may bias the estimate [21]. Differing pre-baseline experiences among samples from different cross-sections (i.e., cohort or generation effect) is likely to be large in China, with dramatic political, eco- nomic, and societal changes in a relative short time. This study used repeated measures of the same individuals to examine the time trends, independent from biologic aging, and have examined the factors related to these trends. The current cohort study is also unique in having small num- bers of people who were taking antihypertensive medica- tion or lipid-lowering medication during the study period. Thus, it is possible to assess the true levels and trends of blood pressure and lipids in the populations. The associations between increasing BMI and increasing blood pressure and lipids suggest that for prevention of the age-related rise in blood pressure and lipid levels, and ultimately of hypertension and hyperlipidemia, it is impor- tant to prevent weight gain, even among the lean popula- tions, when blood pressure and lipids levels are still low. A survey in 2002 in Guangdong Province, where Guangzhou is located, reported that the prevalence of overweight or obesity in adult residents was 28.0% among urban males, 9.9% among rural males, 22.6% among urban females, and Page 7 of 9 9.7% among rural females [22]. Although these preva- lences were much lower than those in Western popula- tions, they were higher than those in our cohorts in 1993- 1994, i.e., 13.4% among male workers, 6.8% among male farmers, 18.4% among female workers, and 6.0% among female farmers. Increasing body weight in the populations accounted for part of the observed changes in risk factor profile among these cohorts. Other factors not measured directly may also contribute to the changes, including the change in body weight. China is undergoing a remarkably fast, yet undesirable, nutritional transition dominated by increasing intake of fat and animal foods [23]. The classic diet in Guangzhou contained high complex carbohydrates and dietary fiber (e.g., cereals, starchy roots), fish, fruits, and vegetables, with few meat and animal foods [24]. Three- day dietary recalls on subsamples of our study cohorts were collected in 255 participants at baseline and 203 par- ticipants in the second re-examination. The average Key score [25]–a measure of intake of saturated fatty acids relative to polyunsaturated fatty acids, as well as the intake of dietary cholesterol - increased among all four gender- occupation groups (a 25% increase overall) [9]. The economy of Guangzhou has changed greatly during the study period. In both urban and rural areas, inflation- adjusted personal income increased five-fold during 1984- 1993 [9]. Prosperous economic growth, commercialization, and availability of foods resulted in more people eating out or eating out more often. The increasing pace of work/and life and time constraints may force people to “eat on the go”. China is no longer a “bicycle country”. Bike use dropped from 34% of total trips to 24% in one decade from 1980s to 1990s in Guangzhou [26]. In contrast, motorized trips increased, including public transport, pas- senger cars, taxi, or motorcycle. Uncontrolled growth of urban sprawl has led to long commutes for workers by buses or trolleybus, passenger cars, or subways [27]. Urba- nization and commercialization have resulted in a more sedentary lifestyle and less work-related or leisure time physical activities. Despite a favorable decreasing trend, smoking remained very common among males at year 10 (60.5% among male workers and 72.0% among male farmers). China is the world’s largest cigarette consumer and producer [28]. It’s state-owned tobacco monopoly generated profit and taxes that were 11% of the central government’s total revenue in 1996 [28]. The tobacco control policy is heavily influenced by economic rather than public health policy. Strong tobacco control efforts are urgently needed in China. Major cardiovascular risk factors were similar in Wes- tern and Chinese populations [29]. This has important implications given the enormous sizes of the populations in China. Blood pressure is strongly and directly related to vascular and overall health, without any evidence of a