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High body mass index (BMI) at ages 16 to 20 was associated with chronic kidney disease (CKD) in early adulthood, a large cohort study showed.

Adjusted hazard ratios for CKD before age 45 ranged from 1.8 to 9.4 across BMI classes in males and 1.4 to 4.3 in females, Gilad Twig, MD, PhD, of Sheba Medical Center in Ramat Gan, Israel, and colleagues reported in .

"It is well recognized that obesity in adulthood is a risk factor for chronic kidney disease, but there is a paucity of knowledge regarding adolescents," Twig told 番茄社区app in an email. "This is relevant especially given the climbing prevalence of overweight and obesity at adolescence that in many Western countries constitute over one third of the population."

In particular, the research team was interested in the occurrence of early kidney disease, which normally presents with albuminuria among individuals in their 20s and 30s, Twig said. "This time in life [is] under-studied as young adults at this age may often be perceived as healthy, and therefore clinical awareness ... may be lower than that in older adults."

Though expecting a strong association, the group was "somewhat surprised by the enormous adjusted risk (up to approximately 10-fold) for those with severe obesity versus those with lean BMI to develop kidney disease," Twig said.

However, risk factors like hypertension or any history of kidney disease excluded participation from the study, "so the population in our study has somewhat better health than the general population," Twig cautioned.

For their study, 593,660 individuals were included in the analysis, which linked screening data from mandatory medical assessments of Israeli adolescents to data from a national healthcare system CKD registry. All 16- to 20-year-olds born since Jan. 1, 1975, were included if they were medically evaluated for mandatory military service through the end of 2019 and insured by an HMO that covered and provided care to about 40% of those obligated to military service.

Follow-up began at the time of medical evaluation or Jan. 1, 2000 (whichever came last), and ended at early CKD onset, death, the last day insured, or Aug. 23, 2020 (whichever came first). A diagnosis of early CKD was 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 [eGFR] of 60 mL/min/1.73 m² or greater. Overall, at a mean follow-up of 13.4 years, 0.3% of individuals developed early CKD.

CKD risk before age 45 was significantly higher for every elevated BMI group compared with normal BMI controls in the cohort. Adjusted hazard ratios for males and females, respectively, were:

• 1.8 and 1.4 with high-normal BMI
• 4.0 and 2.3 with overweight
• 6.7 and 2.7 with mild obesity
• 9.4 and 4.3 with severe obesity

Point estimates were attenuated but still significant for early CKD before 30 years of age. Hazard ratios were 2.2 (95% CI 1.4-3.5) for males with mild obesity and 1.8 (95% CI 1.1-2.9) for females with mild obesity.

Additionally, there were increased HRs from BMIs greater than 20. HRs increased more steeply in males and reached a plateau at a BMI of about 36. Among females, HRs increased steeply for BMIs between 20 and 28, then increased moderately beyond this point.

Risk persisted when the research team calculated HRs for early CKD for the more than 573,000 individuals who did not develop diabetes or hypertension during the study period. Adjusted hazard ratios for early CKD ranged from 1.2 to 2.7 among males and from 1.2 to 2.3 among women across BMI classes.

Limitations of the study included the possibility of ascertainment bias because the diagnosis of CKD requires testing. The research team also lacked longitudinal clinical and lifestyle data about stress, diet, and physical activity.

Additionally, though adolescents were screened using urine dipstick testing, lack of serum creatine measurements could have missed those with reduced eGFR at study entry.

Furthermore, measures of abdominal obesity, such as waist-to-hip ratio, might correlate better than BMI with early CKD. The generalizability of the results was limited by a lack of individuals from West Africa and East Asia in the study population.

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