Analysis of the impact of obesity on the prognosis of IgA nephropathy according to renal function and sex

Few studies have observed the direct effect of obesity on renal prognoses in immunoglobulin A nephropathy (IgAN) or separately evaluated its effects according to sex. We aimed to evaluate the direct and indirect effects of obesity on the renal outcomes of IgAN and observe these effects separately according to renal function and sex. We extracted patients with body mass index (BMI) descriptions from a multicenter retrospective cohort analysis in Japan, and excluded those with < 30 days of follow-up, diabetes mellitus, and steroid treatment. Patients were divided into normal (n = 720; 18.5 ≤ BMI < 25) and obese (n = 212; BMI ≥ 25) groups, which were then compared. The endpoints were a 1.5-fold increase in serum creatinine levels and the initiation of renal replacement therapy. The obese group was older, included more males, and was more likely have hypertension, dyslipidemia, proteinuria, tubular atrophy, and lower renal function than the normal group. Patients with an eGFR < 60 mL/min/1.73 m2 had well-matched characteristics between the groups; however, hypertension, low high-density lipoprotein cholesterol, and hypertriglyceridemia were more common in the obese group. Obesity contributed to tubular atrophy, even when adjusted for renal function. In addition, it contributed to proteinuria only in females. However, obesity itself was not a significant prognostic factor. Although no independent effect on renal prognosis was observed during the study period, the obese group had more risk factors for IgAN progression and obesity contributed to tubular atrophy and female proteinuria. Our results suggest that separately analyzing the prognostic effect of obesity according to sex is important.