Adolescent Obesity Fuels Rising Midlife Stroke Rates

Sue Hughes            

July 05, 2017

The recent increase in midlife stroke rates may be fueled by rising levels of adolescent obesity, a new study suggests.

Investigators at the University of Gothenburg, Sweden, found that an increase in body mass index (BMI) during puberty and adolescence is associated with a raised risk for both ischemic and hemorrhagic stroke in adulthood.

"There isn't much information from medical studies specifically on the adolescent age group.  We looked at BMI at two age groups — age 8, reflecting childhood, and age 20, reflecting young adulthood — to focus on change during puberty. This has not been done before," senior author, Jenny Kindblom, MD, Centre for Bone and Arthritis Research, Institute of Medicine, University of Gothenburg, told Medscape Medical News.

"Our results show that overall at age 8, increased BMI didn't add any extra risk if it had normalized by age 20. But increased BMI between age 8 and 20 did confer a risk of stroke. This suggests that BMI during the adolescent period is more important than BMI during early childhood."

The study was published online June 28 in Neurology.

Opportunity for Intervention

The researchers have also conducted a study of cardiovascular mortality in the same population, with similar results. 

"Our take-home message is that regardless of weight at 8, it is important not to have an increased BMI through adolescence to avoid an increased risk of stroke and cardiovascular death," Dr Kindblom said.

"At age 8 it is not too late to reverse the risk.  That gives hope and an opportunity for intervention.   We need to intervene in a serious way in the early adolescent age group to emphasize the importance of a healthy BMI and lifestyle changes necessary to achieve and maintain that. Our research gives us new evidence that we need to justify this," she added.

For the population-based study, the investigators analyzed data from 37,669 men born in 1945–1961 in Gothenburg.  BMI data at age 8 years was accessed from school records, which were held on a central database for the Gothenburg area, and at age 20 years from national service records, which was compulsory in Sweden until 2008. Information on stroke events was retrieved from national hospital registers.

Participants were followed until 2013. Mean follow-up starting from 20 years of age was 37.6 years.  A total of 918 first stroke events (672 ischemic, 207 hemorrhagic, and 39 undetermined) occurred before the end of follow-up. 

Results showed that BMI increase through puberty and adolescence was independently associated with risk for adult stroke.  Each BMI change of 2

kg/m2 from age 8 to age 20 years was associated with a 21% increased risk for total stroke in adulthood (hazard ratio, 1.21; 95% confidence interval, 1.14 - 1.28).  The risk was increased for both ischemic stroke (HR, 1.19) and hemorrhagic stroke (HR, 1.29).

Independent Stroke Risk Factor

Both boys who became overweight during puberty (HR, 1.81), and boys who were overweight consistently throughout childhood and puberty (HR, 1.71) had increased risk for adult stroke compared with boys who were not overweight as a child or young adult.  

But participants who were overweight at 8 years of age and became normal weight by age 20 did not have increased risk for adult stroke compared with participants with normal weight at both 8 and 20 years of age.

High BMI increase during puberty was also strongly associated with increased risk for adult hypertension (odds ratio per 2-kg/m2 increase of BMI, 1.35), and the researchers propose that the increased risk for stroke is at least partly mediated by an increased risk for hypertension.

Dr Kindblom noted that the study cohort was relatively lean, with just 6.3% being overweight at age 8 and 7.4% at age 20.

"If we did the same study today, we would see much higher rates of overweight. A recent paper reported that 19.4% of children born in 2006 were overweight at age 8. That is a large increase, and the same is seen in young adults. We have a big problem in this regard," she said.   

"It is difficult to change behaviors — we are programmed to like high-calorie food, and our diet has become more processed and our lifestyle more sedentary. We urgently need to reverse this trend.  I'm hoping that our research will help focus efforts on the adolescent population — to identify those at risk and help them lose weight," said Dr Kindblom.

There is a need to increase programs that emphasize sports and healthy eating in youth and encourage young people to make exercise part of their everyday lives, she added. 

Teen Obesity a Global Pandemic

In an accompanying editorial, Kathryn M. Rexrode, MD, Harvard Medical School, Boston, Massachusetts, and Sue Y.S. Kimm, MD, consultant in epidemiology, Santa Fe, New Mexico, note that the strong association between increasing BMI during adolescence and subsequent stroke risk offers one potential explanation for the recently reported dramatic risk in midlife stroke rates.

They note that over the past 3 decades, obesity has reached a pandemic

level globally, especially in the United States, and that between 1988–1989 and 2014–2015, the obesity prevalence in adolescents doubled from 10.5% to 20.5%; extreme obesity among adolescents increased from 2.6% to 9.1%.

On the basis of the data from the current study, "this exponential increase in obesity in adolescents portends serious health consequences later in life," they write.

The editorialists agree with the study authors that the finding that overweight children who reduced their BMI to the normal range by age 20 years had no long-term increased risk for stroke emphasizes the need to target interventions for children and adolescents to prevent overweight and obesity in early adulthood.

"Battling childhood and adolescent obesity is the first step toward prevention of stroke and major adult chronic diseases," they conclude.

The study was supported by the Swedish Research Council, the Swedish government (under the Agreement for Medical Education and Research), the Lundberg Foundation, the Torsten Söderberg Foundation, the Novo Nordisk Foundation, the Knut and Alice Wallenberg Foundation, and the Anna Ahrenberg Foundation. The study and authors and editorialists have disclosed no relevant financial relationships.

Neurology. Published online June 28, 2017. Full text, Editorial

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