Not a good day, news-wise.

From Medscape:

Obesity on All Measures Linked to Increased Ischemic Stroke Risk

Pauline Anderson

January 22, 2010 — No matter how it is measured, obesity is a significant risk factor for ischemic stroke, not only in men and women but also in both blacks and whites, a new study has found.

The study, which used all 3 measures of obesity — body mass index (BMI), waist circumference, and waist to hip ratio (WHR) — was among the first to look at the association between obesity and stroke risk in blacks and whites.

“This was the first study that shows consistently that obesity increases risk of stroke in both blacks and whites,” said lead author Hiroshi Yatsuya, MD, PhD, visiting associate professor in the Division of Epidemiology & Community Health at the School of Public Health, University of Minnesota, Minneapolis.

The study reinforces the message that controlling obesity, which may help prevent hypertension and diabetes, may reduce the risk for stroke, he said.

The study was published online January 21 and will appear in the March issue of Stroke.

Obesity Measurements

The analysis included 13,549 participants (5930 men and 7619 women and 3694 blacks and 9855 whites) aged 46 to 64 years from the Atherosclerosis Risk in Communities (ARIC) Study who were recruited from 4 US communities and followed up from 1987 to 2005.

Participants were interviewed over the telephone and completed several clinic visits.

To determine obesity, researchers used BMI, that is, weight in kilograms divided by height in meters squared, waist circumference alone, and WHR, the ratio of waist circumference taken at umbilical level to hip measurement taken at maximum buttock circumference.

Table. Mean Obesity Measures at Baseline by Race and Sex

Group BMI Waist Circumference Waist to Hip Ratio
Black women 30.8 100.3 0.90
Black men 27.6 96.7 0.94
White women 26.6 93.0 0.89
White men 27.4 99.5 0.97

BMI = body mass index

During follow-up, there were 598 ischemic strokes. Researchers confirmed the incidence of stroke through hospital discharge records and imaging information. Blacks had a 2 to 3 times higher incidence of ischemic stroke compared with whites in each obesity group.

The researchers calculated stroke incidence according to different quintiles of obesity, using all 3 obesity measures. For BMI, they found that the stroke incidence per 1000 person-years ranged from 1.2 for white women in the lowest category to 8.0 for black men in the highest category.

Linear Relationship Between Stroke and Obesity

For other obesity measurements, the stroke incidence rate had a similar range. Using waist circumference, the rates ranged from a low of 1.1 per 1000 person-years for white women in the lowest quintile to 8.2 in black men in the highest quintile. Using WHR, the lowest rate was 1.1 for white women in the lowest category, and the highest was 8.2 for black women in the top category.

No matter what obesity measure was used, the results showed about twice the stroke risk among patients in the highest category compared with those in the lowest. For example, for BMI, the risk for patients in the highest category was 1.4 to 2.1 times higher than those in the lowest BMI category (varying modestly by race and sex).

Dr. Yatsuya noted that the correlation between increasing stroke incidence and increasing degree of obesity was apparent in both races and sexes.

However, said Dr. Yatsuya, much of the association between stroke and obesity in this study could be explained by diabetes and hypertension, both of which are well-established risk factors for stroke.

“Either blood pressure or diabetes mellitus alone could have eliminated significant associations between obesity measure quintiles and ischemic stroke incidence,” the study authors point out.

Given the strong association between obesity and hypertension and other risk factors, including diabetes, they conclude that “obesity would be an important target for prevention of ischemic stroke.”

Best Measure?

There is still a debate in the scientific community about which measure of obesity is most accurate. According to Dr. Yatsuya, BMI might be the easiest to obtain because a clinician just needs to know height and weight. Getting an accurate waist circumference and WHR may be challenging in obese patients, he said.

Using proportion attributable fraction values — the proportion that might be prevented by eliminating a risk factor — the researchers estimated that 18% to 20% of ischemic stroke may be accounted for by a BMI of 28 or more.

Stroke is the third leading cause of death and the leading cause of serious long-term disability in the United States.

Reinforces Obesity Importance

Reached for a comment, Ralph L. Sacco, MS, MD, professor and chair of neurology at the University of Miami in Florida and a member of the American Academy of Neurology, said the study is a “well-done, large, prospective study” that reinforces the importance of obesity as a risk factor not just for heart attack but also for stroke.

One of Dr. Sacco’s own studies, using data from the Northern Manhattan Stroke Study and published in 2003, showed an elevated stroke risk for both blacks and whites using WHR but not BMI (Suk SH, et al. Stroke 2003;34:1586-1592).

“This [new] study is much larger and has much more statistical power and was able to show BMI, as well as waist circumference and waist-to-hip ratio, all great markers for obesity, increased risk in both blacks and whites,” he notes.

Another report from the Northern Manhattan Cohort Study by Dr. Sacco and colleagues, published last year in the Journal of the American College of Cardiology, showed that an elevated waist circumference in both men and women and across whites, blacks, and Hispanics increased the risk not only for stroke but also for myocardial infarction and vascular death (Sacco RL, et al. J Am Coll Cardiol. 2009;54:2303-2311).

All this research is important because obesity is becoming “an alarming trend,” with Americans being less physically active and following unhealthy diets, said Dr. Sacco. “We’re concerned about a higher proportion of the US population that will be obese and at higher risk for high blood pressure, diabetes, and now definitely stroke.”

Dr. Sacco also noted that in this new study, the stroke risk drops after controlling for other factors. “To us, this just means that some of the effect that obesity has is through high blood pressure, diabetes, and other vascular risk factors.”

The ARIC Study was funded by the National Heart, Lung, and Blood Institute. The authors have disclosed no relevant financial relationships.

Stroke. Published online January 21, 2010.

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