作者：Pauline Anderson
出處：WebMD醫學新聞
January 22, 2010 — 一篇新研究發現，不論如何檢測，肥胖都是缺血性中風的顯著風險因素，不論男女、種族都是。
該研究使用了三種測量肥胖的方式：身體質量指數(BMI)、腰圍、腰臀比例(WHR)，首次發現不論是黑人和白人的肥胖都與中風風險有關。
第一作者、明尼蘇達大學公共衛生學院流行病學與社區健康組客座副教授Hiroshi Yatsuya博士表示，這是首次明確指出肥胖增加了黑人和白人之中風風險的研究。
他表示，該研究強調的訊息是，控制肥胖有助於預防高血壓和糖尿病，而降低中風風險。
這項研究線上發表於1月21日，且即將登載於3月的Stroke期刊。
【肥胖測量】
該研究分析了13,549名研究對象(5,930名男性與7,619名女性，3,694名黑人與9,855名白人)，年紀46-64歲，來自「Atherosclerosis Risk in Communities (ARIC)」研究，於1987-2005年間，招募自美國的四個社區且進行追蹤。
研究者以電話對研究對象進行訪談，且完成數次臨床診視。
為了確認肥胖，研究者使用了BMI，也就是體重公斤數除以身高公尺數平方(kg/m2)，腰圍，肚臍處之腰圍與最大臀圍之比例。
表. 根據種族和性別，開始時的肥胖測量
組別 | BMI | 腰圍 | 腰臀比例 |
黑人婦女 | 30.8 | 100.3 | 0.90 |
黑人男性 | 27.6 | 96.7 | 0.94 |
白人婦女 | 26.6 | 93.0 | 0.89 |
白人男性 | 27.4 | 99.5 | 0.97 |
BMI = 身體質量指數
追蹤期間，有598件缺血性中風，研究者透過醫院出院紀錄與影像檢查確認中風發生率，在每個肥胖組中，黑人的缺血性中風發生率高出2-3倍。
研究者使用這三種肥胖測量方法，根據不同的肥胖五分位數計算中風發生率。對於BMI，他們發現，每1000人-年的中風發生率，範圍從最低組的白人婦女的1.2到最高組的黑人男性的8.0。
【中風和肥胖之間的線性關係】
至於其他肥胖測量方法，中風發生率也有類似的範圍，根據腰圍時，每1000人-年的中風發生率，範圍從最低組的白人婦女的1.1到最高組的黑人男性的8.2，根據WHR時，範圍從最低組的白人婦女的1.1到最高組的黑人婦女的8.2。
不論使用哪種肥胖測量方法，結果都顯示，最高組的中風風險幾乎是最低組的2倍，舉例而言，對於BMI，最高組病患的風險是最低BMI組的1.4-2.1倍(根據種族和性別而略有變化)。
Yatsuya博士指出，在這兩個種族和兩性之間，肥胖程度增加都與中風發生率增加有所關聯。
不過，Yatsuya博士表示，本研究中，中風和肥胖的關係大多可以用糖尿病和高血壓來解釋，這兩種疾病都是已經確立的中風風險因素。
研究作者們指出，不論是血壓或糖尿病，都可以消除肥胖測量五分位數與缺血性中風發生率之間的明顯關係。
因為肥胖及高血壓與其他風險因素如糖尿病之間有強烈關係，他們結論表示，肥胖是預防缺血性中風的重要標靶。
【最佳測量方法？】
科學界對於哪種肥胖測量方式最準確仍有所爭辯，根據Yatsuya博士表示，BMI或許是最簡單的方法，因為醫師只要知道身高體重即可，他表示，對於肥胖病患而言，獲得正確的腰圍和WHR可能有點難度。
根據歸因比例值(可以藉由消除一個風險因素而預防的比例)，研究者發現BMI值28以上者佔缺血性中風的18%-20%。
中風是美國第三高的致死原因，也是造成嚴重長期失能的主因。
【強調肥胖的重要性】
美國神經學院會員、邁阿密大學神經科主席、教授、Ralph L. Sacco醫師受邀發表評論時表示，這是一個執行良好的大型前瞻性研究，強調了肥胖不只是心臟病發作的風險因素，也是中風的風險因素。
Sacco醫師的研究之一，使用了「Northern Manhattan Stroke Study」這項研究的資料且發表於2003年，顯示使用WHR測量時，黑人和白人的中風風險也都增加，BMI則無(Suk SH等人，Stroke 2003;34:1586-1592)。
他指出，這個新研究相當大型，統計強度也高出許多，而可以顯示BMI和腰圍與腰臀比例的關聯，這些都是肥胖的重要指標，黑人和白人的風險也都增加。
Sacco醫師等人另一篇來自「Northern Manhattan Cohort Study」的研究報告，發表於去年的美國心臟病學院期刊(Journal of the American College of Cardiology)，顯示不論白人、黑人、西班牙人，男女的腰圍增加不只會增加中風風險，心肌梗塞與血管疾病死亡風險也都增加(Sacco RL等人，J Am Coll Cardiol. 2009;54:2303-2311)。
Sacco醫師表示，這些研究都是重要的，因為肥胖已經成為「令人擔憂的趨勢」，加上美國人少運動且大多是不健康的飲食，我們擔心有更高比率的美國人將會是肥胖的，且有高血壓、糖尿病與中風的高風險。
Sacco也指出，在這篇新研究中，控制其他因素之後，中風風險降低，對我們而言，這意味著肥胖的影響有一部份是因為高血壓、糖尿病與其他血管風險因素。
國家心臟、肺臟與血液研究中心資助ARIC研究，作者們宣告沒有相關財務關係。
Stroke. 線上發表於2010年1月21日。
Obesity on All Measures Linked to Increased Ischemic Stroke Risk
By Pauline Anderson
Medscape Medical News
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.
