Increased BMI Boosts Total and Ischemic Stroke Risk

July 11, 2007 — An analysis of data from a large Finnish cohort, with follow-up of almost 20 years and more than 3200 incident stroke events, shows that increased body mass index (BMI) is a risk factor for both total and ischemic stroke.
Abdominal adiposity, defined as the highest quartile for waist circumference or waist-hip ratio, however, was a risk factor for total and ischemic stroke for men but not for women.
The findings provide yet another reason for those with higher BMIs to try and control their weight, lead author Gang Hu, MD, PhD, from the National Public Health Institute and the University of Helsinki in Finland, told Medscape. "We believe they should reduce their weight because obesity is a very strong risk factor for stroke from this study."
The study is published in the July 9 issue of the Archives of Internal Medicine.
Conflicting Results
Although adiposity is an established risk factor for cardiovascular disease, the relationship with cerebrovascular disease has been less clear, the authors write.
Some studies have shown an association between high BMI and total stroke, particularly ischemic stroke. However, the association disappeared after adjustment for other risk factors, suggesting the effect of BMI might be mediated through those other factors, particularly hypertension, they write. Other studies showed no such association or showed that a low BMI might increase stroke risk.
Several studies have suggested that indicators of abdominal adiposity, such as waist circumference or waist-hip ratio, may be a stronger predictor of stroke than BMI, they note.
This Finnish study, a cross-sectional population survey, is one of the largest cohorts in the world, Dr. Hu said. For this analysis, they investigated the association of BMI, waist circumference, and waist-hip ratio with total and ischemic stroke incidence among 49,996 Finnish men and women who were aged 25 to 74 years and free of coronary heart disease and stroke at baseline.
During an average follow-up of 19.5 years, 3228 subjects (1673 men and 1555 women) had an incident stroke. Of these, 674 were hemorrhagic and 2554 were ischemic.
Data were analyzed dividing BMI levels by World Health Organization (WHO) categories: lean or underweight (BMI, < 18.5 kg/m2), normal weight (BMI, 18.5 - 24.9 kg/m2), overweight (BMI, 25.0 - 29.9 kg/m2), and obese (BMI, ≥ 30.0 kg/m2).
They found that, after adjustment for age, study year, smoking status, physical activity, educational level, family history of stroke, and alcohol consumption, increasing BMI was a risk factor for total and ischemic stroke in both men and women, compared with individuals of normal weight.
Additional adjustment for other factors, including systolic blood pressure, total cholesterol level, and history of diabetes, appeared to attenuate the association, they note, but it remained statistically significant for both sexes.
For hemorrhagic stroke, they found no association with BMI for either men or women if they used the WHO categories. However, when they divided BMI into 7 categories, a U-shaped risk pattern emerged, with increased risk for hemorrhagic stroke seen in women with BMIs at both the lowest and highest BMI levels.
Positive associations of total and ischemic stroke across quartiles of waist circumference or waist-hip ratio were seen for men but not for women. No association of hemorrhagic stroke with either of those variables was seen.
"In conclusion, the present study demonstrates that BMI is associated with an increased risk of total and ischemic stroke in men and women," the researchers write. "Furthermore, a substantial additional risk is mediated through adiposity-related risk factors, such as blood pressure, total cholesterol level and diabetes mellitus."
The study was supported by a grant from the Finnish Academy and by the Finnish Foundation for Cardiovascular Research. The authors have disclosed no relevant financial relationships.
Arch Intern Med. 2007;167:1420-1427.