Overweight and obesity among Israeli adolescents and the risk for serious morbidity in early young adulthood: a nationwide retrospective cohort study.

Background: Morbidities related to obesity are usually associated with its severity and duration. Yet, the onset of serious morbidities in early adulthood among otherwise healthy adolescents with obesity is understudied. We aimed to investigate the association between adolescent BMI and serious morbidities before age 25 years.

Methods: In this nationwide, retrospective cohort study, we included Israeli conscripts aged 17-21 years who underwent pre-recruitment medical evaluation between Jan 1, 1996, and Dec 31, 2017, were deemed medically eligible for military service, and were recruited to the Israeli Defense Forces between 1998 and 2018. Exclusion criteria were missing height or weight or service ineligibility for non-medical or medical reasons. Baseline BMI was converted into age-specific and sex-specific percentiles and classified using the US Centers for Disease Control and Prevention categories. The primary outcome was incidence of serious morbidity disqualifying individuals from completing mandatory service. Participants were followed from enlistment until end of service (3 years for males and 2 years for females), onset of serious morbidity, or Dec 31, 2021. Cox models with adjustment to various socio-economic confounders were applied to calculate the hazard ratio (HR) and 95% CI for serious morbidity for the BMI categories.

Findings: A total of 1 264 355 adolescents aged 16-20 years were assessed for military service. 145 702 were excluded; 144 705 were considered ineligible for service (133 112 for non-medical reasons and 11 593 for medical reasons), and 2867 had missing height or weight data. The study included 1 118 653 individuals (622 989 [55·7%] males and 495 664 [44·3%] females), with 23 347 cases of serious morbidity recorded over 2 534 873 person-years. Incidence of serious morbidity increased across BMI groups in both sexes. Among males, compared with those with normal BMI, the adjusted HRs were 0·89 (95% CI 0·83-0·95) for underweight, 1·21 (1·16-1·27) for overweight, 1·39 (1·32-1·47) for obesity class 1, 2·82 (2·60-3·06) for obesity class 2, and 5·14 (4·37-6·04) for obesity class 3. For females, the respective ratios were HR 0·95 (95% CI 0·84-1·09) for underweight, 1·27 (1·17-1·37) for overweight, 1·63 (1·45-1·82) for obesity class 1, 4·00 (3·46-4·61) for obesity class 2, and 7·30 (5·65-9·43) for obesity class 3. Results persisted in sensitivity analyses restricted to those with unimpaired health at baseline or those in civilian-equivalent office employments.

Interpretation: Obesity in otherwise healthy adolescents was linked with increased risk of serious morbidity before age 25 years. Reducing adolescent obesity will have substantial short-term and long-term health benefits in young adults.

Funding: Sheba Medical Center.