Body Mass Index in Adolescents Related to Risk of Early CKD

The rates of adolescent obesity are increasing. One in five adolescents in the United States have a body mass index (BMI) at or above the 95th percentile for age and sex on the Centers for Disease Control and Prevention (CDC) growth chart. Adolescent obesity has been linked with adverse health outcomes later in life, including diabetes, cardiovascular diseases, cancer, and all-cause mortality.

There is a recognized link between obesity and chronic kidney disease (CKD) in adults. However, there are few data available on the link between adolescent obesity and early CKD. Further, it is unknown whether an association between adolescent obesity and early CKD is independent of other comorbidities, such as diabetes and hypertension.

Researchers, led by Avishai M. Tsur, MD, MHA, conducted a study to examine the association between adolescent BMI and early CKD in young adulthood, defined as under 45 years of age. Results of the retrospective cohort study were reported in JAMA Pediatrics.

The study linked screening data of mandatory medical assessments of Israeli adolescents to data from a CKD registry of a national health care system. The cohort included Israeli adolescents who were 16 to 20 years of age; born since January 1, 1975; medically evaluated for mandatory military service through December 31, 2019; and insured by the Maccabi Healthcare Services. Exclusion criteria were kidney pathology, baseline albuminuria, hypertension, dysglycemia, or missing data on blood pressure or BMI at the time of the baseline assessment. Individuals whose follow-up ended prior to the establishment of the CKD registry were also excluded.

The outcome of interest was a diagnosis of early CKD, based on at least two results of a urine albumin-creatinine ratio of 30 mg/g or greater within 6 months of a serum creatinine test that showed an estimated glomerular filtration rate of 60 mL/min/1.73 m² or greater (determined using the Chronic Kidney Disease Epidemiology Collaboration creatinine equation). Test results were automatically extracted, and the date of the first positive test result was determined as the date of early CKD.

BMI was calculated as weight in kilograms divided by height in meters squared and categorized by age- and sex-matched percentiles according to the CDC. Follow-up began at the time of medical evaluation or January 1, 2000 (whichever came last), and ended at early onset CKD, death, the last day insured, or August 23, 2020 (whichever came first). Data analysis was performed from December 18, 2021, to September 11, 2023.

A total of 629,168 adolescents were evaluated during the study. Of those, 5.6% were excluded from the analysis, resulting in a final cohort of 593,660 adolescents (54.5% [n=323,293] male and 45.5% [n=270,367] female). Of these, 5.9% (n=35,056) were categorized as underweight, 43.3% (n=256,968) had low-normal BMI, 35.3% (n=209,485) had high-normal BMI, 10.0% (n=60,516) were overweight, 4.3% (n=25,304) had mild obesity, and 1.1% (n=6331) had severe obesity. Mean age at study entry was 17.2 years and was similar across groups. Mean age at study entry was 17.3 years for males and 17.2 for females.

For both males and females, the normal BMI groups had the highest proportions of high residential socioeconomic status, high cognitive performance, complete education, and unimpaired health.

There was an interaction among BMI group, sex, and early CKD in adulthood. In males, the reported incidents of early CKD by adolescent BMI group were: underweight, 0.17% (n=40); low-normal BMI, 0.15% (n=211); high-normal BMI, 0.25% (n=263); overweight, 0.50% (n=169); mild obesity, 0.78% (n=135); and severe obesity, 0.93% (n=38). Mean follow-up was 13.4 years, including 4,316,217 person-years. Corresponding rates per 10,000 person-years were 1.25 for males who were underweight in adolescence, 1.10 for low-normal BMI, 1.86 for high-normal BMI, 4.10 for overweight, 6.54 for mild obesity, and 8.43 for severe obesity.

For females, the reported incidents of early CKD were: underweight, 0.38% (n=46); low-normal BMI, 0.30% (n=364); high-normal BMI, 0.41% (n=421); overweight, 0.68% (n=188); mild obesity, 0.79% (n=64); and severe obesity, 1.07% (n=24). Mean follow-up was 13.4 years. The corresponding rates per 10,000 person-years were 2.75 for females who were underweight in adolescence, 2.24 for low-normal BMI, 3.08 for high-normal BMI, 5.34 for overweight, 6.53 for mild obesity, and 9.64 for severe obesity.

Among males, the adjusted hazard ratios for early CKD were 1.8 (95% CI, 1.5-2.2) for adolescents with high-normal BMI, 4.0 (95% CI, 3.3-5.0) for those who were overweight, 6.7 (95% CI, 5.4-8.4) for those with mild obesity, and 9.4 (95% CI, 6.6-13.5) for those with severe obesity. Corresponding values among females were 1.4 (95% CI, 1.2-1.6), 2.3 (95% CI, 1.9-2.8), 2.7 (95% CI, 2.1-3.6), and 4.3 (95% CI, 2.8-6.5), respectively.

In subgroup analyses of cohorts limited to those who were seemingly healthy as adolescents, those surveyed up to 30 years of age, and those free of diabetes or hypertension at the end of the follow-up, results were similar.

Limitations to the study cited by the authors included the possibility of ascertainment bias, the lack of longitudinal clinical and lifestyle data, and the lack of serum creatinine measurements.

In summary, the researchers said, “In this cohort study, high BMI late in adolescence was associated with early CKD in young adulthood, which can occur even in seemingly healthy individuals with high-normal BMI and before the age of 30 years. Given the increasing obesity rates among adolescents, our findings are a harbinger of the potentially preventable increasing burden of CKD and subsequent cardiovascular disease.”

Source: JAMA Pediatrics