A community-based cross-sectional and longitudinal study uncovered asymptomatic proteinuria in Japanese adults with low body weight.

Although proteinuria is highly prevalent in obese individuals, the association between proteinuria and low body weight is equivocal. In this study we determine whether low body weight is more strongly associated with proteinuria compared with normal weight. The association between body mass index (BMI) and proteinuria was examined in a cross-sectional study of 62,582 asymptomatic individuals aged 20-70 years without known kidney diseases recruited, based on the results of medical checkups in 1999. We also examined the incidence of recurrent or nonrecurrent proteinuria in an 8-year longitudinal analysis of 12,493 individuals without proteinuria at baseline. The prevalence of proteinuria showed a J-shaped relationship with BMI. Multivariate regression analysis showed that BMI of 27.0 kg/m(2) and above or 18.9 kg/m(2) and less was significantly associated with proteinuria relative to BMI 21.0-22.9 kg/m(2), even after adjusting for relevant cardiometabolic risk factors. In the longitudinal study, similar J-shaped relationships between the incident rates of proteinuria and baseline BMI groups were observed at post-baseline checkups. Baseline BMI 27.0 kg/m(2) and above was associated with significantly greater risk for recurrent and nonrecurrent proteinuria, whereas BMI 18.9 kg/m(2) and less was only associated with nonrecurrent proteinuria. Thus, obesity and low body weight may be associated with different types of proteinuria independent of cardiometabolic risk factors.