Is obesity in the Asia-Pacific body mass index classification associated with new-onset chronic kidney disease in non-diabetic Japanese men and women?

Background/Objectives: Obesity is a risk factor for the development of chronic kidney disease (CKD). However, little is known about the relationship between the Asia-Pacific body mass index classification (Asia-Pacific classification) and the subsequent development of CKD in non-diabetic Asian men and women. Subjects/Methods: Body mass index (BMI) was categorized in accordance with the Asia-Pacific classification: underweight (< 18.5 kg/m2), normal weight (18.5–22.9 kg/m2), overweight (23.0–24.9 kg/m2), obesity class I (25.0–29.9 kg/m2), and obesity class II (≥ 30.0 kg/m2). Using administrative checkup data for non-diabetic Japanese adults (1998–2023), we assessed the relationship between the Asia-Pacific classification and new-onset CKD by sex. The Weibull accelerated failure time model was selected because the proportional hazards assumption was violated. Results: In total, 34.2% of 3,098 men and 34.8% of 4,391 women had newly developed CKD. The mean follow-up time was 7.41 person-years for men and 8.25 person-years for women. Compared with those of normal weight, obesity class I was associated with a 6% (95% confidence interval [CI]: 2%–10%) shorter time to CKD development in men and a 6% (95% CI: 2%–9%) shorter time to CKD development in women. Obesity class II was associated with the shortest survival to CKD onset by point estimate in men but had an almost null value in women (i.e., 95% CIs crossed 1 in all of the models). Conclusions: Among non-diabetic Japanese men and women, obesity class I in the Asia-Pacific classification was associated with a shorter survival time to CKD onset than normal weight. Low point estimates for obesity class II suggested a dose-response relationship in men but a less clear relationship in women. The conventional cutoff value for obesity, BMI ≥ 30.0 kg/m2, may be too high a risk factor for new-onset CKD in non-diabetic Asians, regardless of sex. ### Competing Interest Statement Okawa declares a relationship with Zentsuji City that includes employment. Mitsuhashi and Tsuda declare no potential competing interests. ### Funding Statement This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The Ethics Committee of Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences and Okayama University Hospital approved this study (No. K1708-040). The Ethics Committee waived the need for informed consent. Study procedures were performed in accordance with the Declaration of Helsinki and Japanese Ethical Guidelines for Medical and Biological Research Involving Human Subjects. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present work are contained in the manuscript and its supplementary information files.