Previous studies have reported the association between development and progression of chronic kidney disease (CKD) and socioeconomic status including income, educational attainment and residential area. It has been shown that people with low socioeconomic status have higher risk of CKD. However, most reports are from the US, where public universal health coverage does not exist, and little is known about the situation in the countries with universal health coverage, such as Japan. Dr. Nana Ishimura in Doctoral program, Dr. Kosuke Inoue and Professor Naoki Kondo from Department of Social Epidemiology, Professor Sayaka Nakamura from Sophia University and Professor Shiko Maruyama from Jinan University investigated the association between income level and impaired kidney function using data from the nationwide database managed by the Japan Health Insurance Association, which included approximately 5.6 million individuals.
In their study, the subjects were insured individuals in the Japan Health Insurance Association. They categorized the subjects into income deciles and investigated whether there was any difference in the risk of impaired kidney function across the income levels. They evaluated rapid CKD progression (defined as an annual eGFR decline of more than 5 mL/min/1.73 m2) and initiation of kidney replacement therapies (hemodialysis, peritoneal dialysis or kidney transplant). Then, they showed that the risk of rapid CKD progression in the lowest income group, whose average income per month was \136,451, was 1.7 times higher than that of the highest income group, whose average monthly income was \825,236. Similarly, the risk of kidney replacement therapy initiation in the lowest income group was 1.65 times higher compared to that of highest income group.
This study showed that there was a disparity based on income in the risk of impaired kidney function both among males and females even in Japan with extensive health care system including universal health coverage and annual health examinations. In order to provide people with fairer and more efficient medical care, they suggest that it is important to construct the living environment and support system to maintain healthy lifestyle required for the control of kidney function as well as financial support under universal health coverage. Furthermore, it is necessary to investigate the difference in lifestyle and quality of treatment, social stress and the effect of environment to find the related mechanisms.
This study was published online in the international journal, JAMA Health Forum, on March 2nd, 2024 in Japan time.

Ishimura N, Inoue K, Maruyama S, Nakamura S, Kondo N. Income Level and Impaired Kidney Function Among Working Adults in Japan. JAMA Health Forum. 2024;5(3):e235445. doi:10.1001/jamahealthforum.2023.5445
Corresponding to: inoue.kosuke.2j@kyoto-u.ac.jp
Link：
・https://jamanetwork.com/journals/jama-health-forum/fullarticle/2815746
・https://www.kyoto-u.ac.jp/ja/research-news/2024-03-04-1