U-shaped association between body mass index and proteinuria in a large Japanese general population sample.

BACKGROUND: There is little data on the association between body mass index (BMI) and proteinuria.

METHODS: This was a cross-sectional cohort study assessing the association between BMI and proteinuria in a large Japanese population. Using a nationwide health check-up database of 212,251 Japanese aged >20 years with no pre-existing cardiovascular diseases (185,183 men, median age 66 years; 127,068 women, median age 65 years), we examined the association between BMI and proteinuria (≥ 1+ on dipstick).

RESULTS: Subjects were divided into 11 subgroups by BMI grading in 1 kg/m(2) intervals from 18.5-27.5 kg/m(2). A BMI of approximately 22 ± 0.5 kg/m(2) was considered optimal for Japanese; therefore, this subgroup was set as a reference when logistic analysis was applied. Age, waist circumference, height, weight, smoking and drinking habits, use of medications such as antihypertensive, antidiabetic, or antihyperlipidemic, as well as proteinuria, estimated glomerular filtration rate (eGFR), chemistry data, and blood pressure levels were significantly different between subgroups in both genders. The odds ratio for proteinuria showed a U-shape in men and women, even after adjustment for significant covariates such as age, waist circumference, systolic blood pressure, eGFR, fasting plasma glucose, triglyceride, low-density lipoprotein, antihypertensive use, antidiabetic use, antihyperlipidemic use, and lifestyle factors (smoking and drinking). Gender differences were also prominent--a BMI <20.4 kg/m(2) was significantly associated with proteinuria in men compared to a BMI <18.4 kg/m(2) in women. On the other hand, a BMI ≥ 25.5 kg/m(2) was also significantly associated with proteinuria in men compared to a BMI ≥ 22.5 kg/m(2) in women.

CONCLUSIONS: We found that BMI levels were associated with proteinuria in a U-shaped manner and showed marked gender differences. Health guidance should not only focus on higher BMI subjects, but also on thin subjects, in terms of the prevention of chronic kidney disease.