Long-term effects of socioeconomic status on the incidence of decreased glomerular filtration rate in a Southeast Asian cohort

Background There is limited information on the role of low socioeconomic status (SES) in the development of new chronic kidney disease (CKD) in the general population, especially from developing countries. This study will test the hypothesis that low SES increases the risk of incidence of decreased glomerular filtration rate (GFR, used as an estimate for CKD) in a Thai worker cohort. Method In this prospective, longitudinal observational study, we evaluated the association of income and educational attainment on incident decreased GFR (iGFR <60 mL/min/1.73 m 2) over a 27-year period in employees of Electricity Generating Authority of Thailand. In 1985, subjects participated in a health survey and were re-examined in 1997, 2002, 2007 and 2012. Education was classified into three categories: low, 0-8th grade; medium, 9-12th grade; and high, >12th grade. Income was categorised as follows: low <10 000 Thai Baht (THB)/month; medium, 10 000-20 000 THB/month; and high, >20 000 THB/month. HRs of iGFR<60 mL/min/1.73 m 2 were estimated using Cox interval-censored models with high income or education as the reference groups after adjustments for clinical risk factors. Results Participants (n=3334) were followed for 23 (15, 27) years. When evaluated separately, both education and income were risk factors for iGFR<60 mL/min/1.73 m 2 (adjusted HR education: medium - 1.26 (95% CI 1.13 to1.42) and low - 1.57 (95% CI 1.36 to 1.81) and adjusted HR income: medium - 1.21 (95% CI 0.97 to 1.50) and low - 1.47 (95% CI 1.18 to 1.82)). When both income and education were included together, low and medium education remained independently associated with iGFR<60 mL/min/1.73 m 2. Conclusions Low education was independently associated with increased risk of decreased GFR in a Thai worker population. Strategies to identify risk factors among low SES may be useful to prevent early CKD.