Setareh Salehi Omran, MD
Despite a decline in stroke hospitalizations among older adults within the United States, there is an increasing incidence of stroke in young adults. Multiple factors are thought to play a role, including a possible increase in atherosclerotic risk factors such as obesity among young adults. Adolescent obesity is an ongoing epidemic that can lead to several complications, including diabetes, metabolic syndrome, and cardiovascular disease. Several studies have shown an association between adolescent obesity and subsequent risk of stroke in older age. It is unclear whether adolescent obesity is associated with the development of stroke in young adults.
Using data from the Israeli National Stroke Registry, Bardugo et al. examined the incidence and association between adolescent obesity and stroke in the young in Israel. Their study included all adolescents who underwent a medical evaluation prior to their mandatory military service between 1985 and 2013. The medical evaluation included information on demographics, vascular risk factors, and body mass index (BMI). BMI values were grouped according to percentiles for age and sex established by the U.S. CDC: underweight (less than 5th percentile), low-normal BMI (5th to 49th percentile), high-normal BMI (50th to 84th percentile), overweight (85th to 94th percentile), or obese (>95th percentile). The primary outcome was a first stroke event as recorded in the national registry between 2014 and 2018. Importantly, data was unavailable for patients who developed a stroke before 2014. Cox proportional hazard models were used to estimate the hazard ratios (HRs) for incidence stroke using the low-normal BMI as the reference group. In addition to a crude HR, the authors also performed three additional analyses adjusted for: 1) sex and age; 2) sex, age, and socio-demographic values; 3) sex, age, socio-demographic values, and diabetes status at beginning of follow-up. The authors also performed several sensitivity and subgroup analyses, including analyses restricted by diabetes status and optimal blood pressure at adolescence.
A total of 1,900,384 individuals were included in the study (mean age at time of medical evaluation was 17.3 years, 58% men). The mean age at beginning of follow-up was 31.1 (range; 16.2 – 49.0 years). During a cumulative follow-up period of 9,482,130 person-years, there were 1,088 incident cases of a first stroke event, of which 921 were ischemic and 167 hemorrhagic. The incidence rate of any stroke and ischemic stroke gradually increased across BMI categories. There was no association between hemorrhagic stroke and BMI. In adjusted analysis, higher adolescent BMIs were associated with first ischemic stroke (HR 1.4, 2.0, and 3.4 for the high-normal BMI, overweight, and obese groups, respectively). The results remained unchanged when stratifying the cohort based on diabetes status and optimal blood pressure in adolescence. Additionally, when stratifying patients based on age at the time of ischemic stroke, adolescents that were overweight and obese were more likely to have an ischemic stroke before the age of 30.
The main strengths of this study lay in its use of a large, representative population of Israel. The presence of a central database, the Israel National Stroke Registry, also ensures that all outcomes are being correctly identified. The study has several noteworthy limitations. First, there is a lack of data on the stroke mechanisms. It would be interesting to know whether individuals with high BMI were more likely to have stroke secondary to large artery atherosclerosis, small vessel disease or other etiologies. Second, the authors did not have access to childhood and adult BMI data, which limited their ability to assess the independent risk of adolescent BMI. Third, outcomes were only available from 2014 to 2018, and may have missed patients that had a stroke before this time period. Overall, the findings add to the urgency of addressing the obesity epidemic by increasing our understanding of the relationship between adolescent BMI and future stroke risk in young adults.