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Retrospective analysis of height and weight measures from school and military records and long-term stroke follow-up data in Swedish men revealed that a BMI increase of 2 kg/m2 from ages 8 through 20 was associated with a 21% increased risk of total stroke in adulthood (HR 1.21 per SD increase), according to Jenny Kindblom, MD, PhD, of the University of Gothenburg in Sweden, and colleagues.
In addition, the risk of ICH was increased by 29% for each 2 kg/m2 increase in BMI (HR 1.29 per SD increase), and the risk of ischemic stroke rose by 19% (HR 1.19 per SD increase), they reported online in Neurology.
A large increase in BMI during puberty and adolescence was also associated with a 35% increased risk of adult hypertension (OR 1.35 per SD increase), making it a probable mediating factor, the researchers said.
The good news? In boys who were overweight at age 8 but whose BMI normalized by age 20, there was no increased risk of stroke during adulthood, they reported.
"The observational nature of our study precludes making conclusive statements about the observed associations, but our findings can be useful for hypothesis generation," the researchers wrote. "Based on our findings in the present study, we hypothesize that avoiding excessive BMI increase during puberty might reduce the risk of adult stroke and that one should consider monitoring adult blood pressure in men with excessive BMI increase during puberty."
Although a high BMI in adulthood is a risk factor for stroke, there is no clear evidence of an association between prepubertal BMI and adult risk of stroke, the study authors said. "All these previous studies had only one BMI measurement available and could not separate the effect of BMI at childhood and the effect of BMI increase through puberty and adolescence for stroke risk," they wrote.
Only BMI increase through puberty and adolescence was independently associated with risk of adult stroke, they emphasized. Sub-analysis showed that a large BMI increase during puberty was a moderate risk marker of ischemic stroke in adult men whether they were younger or older than 55 years. It also was a substantial risk marker for early adult ICH and a strong predictor of adult hypertension.
For the study, the investigators used data from the population-based BMI Epidemiology Study (BEST) of 37,669 men born between 1945 and 1961 in Gothenburg, Sweden.
Men with information on BMI both at age 8 and at age 20 were followed until December 2013, for an average of 38 years.
Information on stroke events from national registries showed that there were 918 first stroke events, 672 ischemic stroke events, and 207 ICH events. Data also showed that:
- In 33,511 men of normal weight at both age 8 and age 20, 779 had a stroke (2.3%)
- In 1,800 men whose weight was normal at age 8 but who were overweight at age 20, 67 had a stroke (3.7%)
- In 1,368 men who were overweight at age 8 and of normal weight at age 20, 36 had a stroke (2.6%)
- In 990 men who were overweight at both time points, 36 had a stroke (2.6%)
In an accompanying editorial, Kathryn Rexrode, MD, MPH, of Harvard Medical School, and Sue Kimm, MD, MPH, an epidemiology consultant in Santa Fe, N.M., said this study demonstrates the clinical significance of BMI changes during adolescence -- "a relatively quiescent time in medical surveillance."
"These findings emphasize the need to target interventions for children and adolescents to prevent overweight and obesity in early adulthood and also reduce future cardiovascular morbidity," they wrote. "Battling childhood and adolescent obesity is the first step toward prevention of stroke and major adult chronic diseases."
The study's findings offer a potential explanation for the sharp increases in the incidence of stroke at mid-life in the U.S., Rexrode and Kimm pointed out, noting that the incidence of stroke in women ages 35-54 has tripled over the past 20 years, corresponding to epidemic rises in obesity.
Rates of obesity are continuing to climb in children and adolescents in the U.S., from age 6 right through age 19. In adolescents, obesity rates have doubled (10.5% to 20.5%) and rates of extreme obesity have quadrupled (2.6% to 9.1%), a development that "portends serious health consequences later in life," the editorialists said.
Limitations of the study included the fact that no information on childhood socioeconomic factors or education was available and researchers couldn't control for risk factors such as smoking, exercise, serum blood lipid levels, or BMI at middle age. In addition, the cohort was comprised primarily of Caucasian men and the prevalence of obesity in the cohort was relatively low compared to today's rates.