Characteristics of selected study participants
A total of 256,782 participants were surveyed from 2014 to 2020 in Beijing and 697,170 participants surveyed from 2012 to 2020 in Hunan were enrolled in our study.
Overall, the mean BMI was 23.91 (95% CI: 23.90, 23.92) kg/m2 and 108,914 participants (11.41% [95% CI: 11.34%, 11.47%]) were obese. Table 1 shows the demographic and clinical characteristics of the study participants by obesity status. Compared to the non-obese, participants in the obese group were more likely to be male, from Beijing, older, with higher level of TC, TC, LDL-c, and FSG, having elevated blood pressure, with hypertension, diabetes or hyperlipidemia (p<0.001, Table 1).
Trends in BMI and obesity
The age- and sex-standardized mean BMI levels between Beijing and Hunan participants were 23.94 (95%CI: 23.93, 23.95) and 23.68 (95%CI: 23.67, 23.69) kg/m2, respectively (Table 2). During 2014- 2020, the BMI levels in Beijing showed significant nonlinear changes by surveyed year (P<0.001) and grew rapidly after 2018 (Figure 1). A nonlinear trend in BMI level among female from Hunan was also observed, which increased from 2012 to 2016 and declined after 2016. However, a significant and linear increasing trend in BMI trend was observed among the Hunan male population (P<0.001) (Figure 1). Due to the interaction between the BMI and age, we further stratified the population by age. As a result, the BMI level was found to significantly increased among 20-39 aged groups in both area, and the trends between Hunan male and Beijing female groups were linear. Among the 40-59 years old, nonlinear upward trends were observed in both sexes from Beijing and Hunan. On the other hand, a significant and downward trend in BMI was found among female participants over 60 from Hunan (Table S1 and Figure S2).
Between 2014 and 2020, the prevalence of obesity among Beijing participants increased from 12.70% (95% CI: 12.17%, 13.23%) to 14.33% (95% CI: 13.97%, 14.70%) (P=0.009) (Fig 2A). The obesity prevalence among Beijing females and males showed similar annual percentage changes. Among the 20-39 and 40-59 age group, the annually percentage changes were 6.07 (95% CI: 3.97, 8.21) and 3.17 (95% CI: 1.02, 5.37), respectively. However, the trends of obesity in the over 60 years age group were nonsignificant (P=0.668) (Fig 2B-D).
The trends of obesity among Hunan participants were different from those among Beijing participants. Between 2012 and 2020, no significant trend in obesity was found among the total sample of Hunan participants (P=0.240) (Fig 2A). After stratification by age and sex, the prevalence of obesity among females and males aged 20-39 years was found to increase from 1.87% (95% CI, 1.63%, 2.11%) to 2.99% (95% CI, 2.69%, 3.29%) and from 13.10% (95% CI, 12.53%, 13.67%) to 16.04% (95% CI, 15.34%, 16.74%), respectively (Fig 2B). However, obesity among over 60 years old Hunan females showed significant decreasing trends (P <0.006), and among 40-59 years aged Hunan females, the prevalence of obesity increased between 2012 and 2014 (slope=0.12 (95% CI: -0.07,0.30), P=0.17), and decreased after 2014 (slope=-0.03 (95% CI: -0.06, 0.00), P=0.04) (Fig 2C, D).
Trends in metabolic factors
Overall, a total of 908,311 persons were included for metabolic analysis. The age-adjusted means of FSG, TG, HDL-c, SBP and DBP are listed in Supplementary Tables S2-S6. Overall, the change trend in metabolic factors was similar between different sexes but show regional differences expect for in FSG, which were both rising in the two places (Figure S3). The TG levels showed a downward trend in 2014-2018 and an upward trend in 2018-2020 among Beijing population, and in the Hunan region it showed a non-linear monotonous rising trend (Figure S4). The HDL-c levels had opposite trends in the two places, with Beijing rising and Hunan declining (Figure S5). The SBP levels showed an upward trend in Beijing, and in the Hunan region it showed a downward trend in 2012- 2016 and an upward trend in 2016-2020 (Figure S6). The DBP levels rose first and then fell in Beijing, and fell first and then rose in Hunan (Figure S7).
Trends of obesity phenotypes
Between 2014 and 2020, among Beijing participants, the prevalence of the MUNO subtype significantly decreased from 36.03% (95% CI: 35.16%, 36.90%) to 27.85% (95% CI: 27.31%, 28.39%) with an annual percentage change of -6.53 (95% CI: -12.33, -0.34) (Fig 3B), but the trends in MUO were nonsignificant (p=0.384) (Fig 3D). However, the trends in MHNO were nonsignificant and the prevalence of MHO increased significantly from 2.07% (95% CI: 1.84%, 2.30%) to 4.33% (95% CI: 4.13%, 4.53%) (Fig 3C). All obesity phenotypes in different sex and age groups among Beijing participants showed similar annual percentage changes (Fig S8).
Unlike the trends in obesity phenotypes among Beijing participants, between 2012 and 2020, the prevalence of the metabolically unhealthy subtypes MUNO and MUO among Hunan participants increased significantly from 21.92% (95% CI: 21.55%, 22.30%) to 29.58% (95% CI: 29.10%, 30.07%) and from 5.36% (95% CI: 5.18%, 5.54%) to 7.35% (95% CI: 7.11%, 7.58%), respectively (Fig 3B, D). Meanwhile, the prevalence of the metabolically healthy subtypes MHNO and MHO decreased significantly from 69.24% (95% CI: 68.57%, 69.92%) to 60.21% (95% CI: 59.55%, 60.88%) and from 3.47% (95% CI: 3.32%, 3.61%) to 2.86% (95% CI: 2.71%, 3.00%), respectively (Fig 3A, C). Among Hunan participants aged 40-59 and over 60 years old, females and males showed a similar annual percentage change in all obesity phenotypes (Fig S8), but among the 20-39 year age group, the prevalence of MUNO and MUO in females showed a greater annual percentage increase than that in males (14.84 [95%CI: 9.40, 20.56] vs 5.18 [95% CI: 2.62, 7.81] and 15.02 [95% CI: 13.55, 16.51] vs 5.32 [95% CI: 3.74, 6.92]) (Fig S8).