Re-examining the reversal hypothesis: A nationwide population-based study of the association between socioeconomic status, and NCDs and risk factors in China.

Background: According to the reversal hypothesis, as a country's economic and social development progresses, the burden of NCDs and risk factors shifts from rich to poor. The aim of this research is to examine the reversal hypothesis in the Chinese setting. Methods: Using data from the China Health and Retirement Longitudinal Study (CHARLS) in 2015, we explored whether the reversal hypothesis applies at the subnational level. Participants aged 45 years and older in 2015 were included. We examined five risk factors (smoking, heavy drinking, physical inactivity, overweight, and obesity) and three objectively measured NCDs (diabetes, hypertension, dyslipidemia). Binary logistic regressions were performed to examine outcomes across people of differing SES in provincial level, in urban and rural areas, and across generations. Results: Nationally, SES is positively associated with heavy drinking, obesity, diabetes and dyslipidemia, whereas it is negatively associated with physical inactivity. The association between SES and smoking and hypertension was not statistically significant. Except in the cases of diabetes and dyslipidemia, we found that risk factors of all kinds were more concentrated among richer people in rural than in urban areas. Across provinces with increasing GDP per capita, a downward trend in risk factors among those with high SES compared to those with low SES could be interpreted, while the opposite trend could be interpreted with respect to the metabolic syndrome conditions. Obesity and overweight exhibited slight downward trends (in line with those for risk factors) and upward trends (in line with those for metabolic syndrome conditions), respectively. Conclusion: We conclude that China is at a relatively early stage of 'reversal', visible with respect to risk factors. If these patterns persist over time, the trend will likely feed through to metabolic disorders which will increasingly become diseases of the poor.