為什么人們對(duì)于這樣一種隨處可見的飲品會(huì)有如此多的困惑？畢竟，有大約54%的美國成年人經(jīng)常喝咖啡──他們每天大概要喝掉四億杯咖啡。而且，咖啡還是世界上交易范圍第二大的商品，僅次于石油。
Why is there so much confusion about something that's so ubiquitous? After all, some 54% of American adults drink coffee regularly-an estimated 400 million cups per day-and coffee is the second most widely traded commodity in the world, after oil.
　　
首先，絕大多數(shù)針對(duì)咖啡的研究都來自于觀察。研究人員通過研究多年來大量的數(shù)據(jù)來尋找人們的習(xí)慣和健康之間的關(guān)系。
For starters, the vast majority of coffee studies to date have been observational, in which researchers examine large sets of data over many years, looking for patterns in peoples' habits and their health.
　　
但是，研究對(duì)象并不總是能準(zhǔn)確記憶或者準(zhǔn)確報(bào)告他們飲用咖啡的數(shù)量?？Х缺娜萘繌?盎司到32盎司不等；咖啡因的含量也從75毫克到近300毫克不等。而加上白糖、香料糖漿和奶油可以讓一杯本來低脂、基本沒有卡路里的飲料變成一杯冰激凌蘇打飲料。
But subjects don't always remember or report accurately on how much they drink. Cup sizes can range from 6 to 32 ounces; caffeine loads can vary from 75 to nearly 300 milligrams. Loading up with sugar, flavored syrup and whipped cream can turn a no-fat, almost no-calorie drink into the equivalent of an ice-cream soda.
　　
即便是那些精心設(shè)計(jì)、對(duì)這些變量已作調(diào)整的觀察性研究也只能發(fā)現(xiàn)其中的相關(guān)性，而無法證實(shí)一種因果關(guān)系。對(duì)于為什么大量飲用咖啡的人患病幾率較小的問題，也許還有其它難以觀察到的原因，比如這些人擁有一份收入穩(wěn)定的工作、能夠得到醫(yī)療保障、經(jīng)常鍛煉身體，在飲食方面也更健康。相反，“那些自我感覺不那么健康的人一天喝上六杯咖啡的可能性更小。……這只是一種可能性，”杜克大學(xué)醫(yī)學(xué)中心(Duke University Medical Center)的心理生理學(xué)家吉姆?雷因(Jim Lane)表示。雷因?qū)Х纫蛐в玫难芯恳呀?jīng)超過了25年。
Even carefully constructed observational studies that correct for such variables can only find correlations, not prove a cause-and-effect relationship. There may be other, hidden reasons why people who drink a lot of coffee have a lower risk of illness-such as jobs that provide a steady income and access to health care, exercise and healthier food. Conversely, 'people who don't feel that healthy may be less likely to drink six cups of coffee a day. ... It's just a possibility,' says Jim Lane, a psychophysiologist at Duke University Medical Center who has studied the effects of caffeine for more than 25 years.
　　
風(fēng)險(xiǎn)消失
Risks Disappear
　　
實(shí)際上，許多數(shù)十年前的研究認(rèn)為喝咖啡可能導(dǎo)致更高的患癌風(fēng)險(xiǎn)的原因在于，他們顯然將一些與喝咖啡有關(guān)的習(xí)慣也考慮在內(nèi)了。一旦研究人員開始調(diào)整研究對(duì)象，比如將那些吸煙者排除在外，額外的癌癥風(fēng)險(xiǎn)也就消失了。
Indeed, many studies from earlier decades that linked coffee drinking to a higher risk of cancer were apparently detecting related habits instead. Once researchers started adjusting for study subjects who also smoked cigarettes, the additional cancer risk disappeared.
　　
“當(dāng)我進(jìn)入醫(yī)學(xué)院的時(shí)候，人們告訴我喝咖啡對(duì)身體有害。不過在上世紀(jì)90年代以及近十年，人們開始清楚地認(rèn)識(shí)到，如果采用正確的方法進(jìn)行這些研究，那么他們就會(huì)發(fā)現(xiàn)咖啡能夠保護(hù)公眾健康，”范德堡大學(xué)(Vanderbilt University)精神病學(xué)和藥理學(xué)教授、該?？Х妊芯繀f(xié)會(huì)負(fù)責(zé)人彼得?馬丁(Peter R. Martin)表示。該校的咖啡研究協(xié)會(huì)在咖啡生產(chǎn)國的資助下于1999年成立。
'When I went to medical school, I was told that coffee was harmful. But in the '90s and this decade, it's become clear that if you do these studies correctly, coffee is protective in terms of public health,' says Peter R. Martin, a professor of psychiatry and pharmacology at Vanderbilt University and director of the school's Institute for Coffee Studies, founded in 1999 with a grant from coffee-producing countries.
　　
盡管如此，許多研究人員仍然認(rèn)為，對(duì)于像咖啡這樣的東西，得出確切結(jié)論的唯一方法是通過實(shí)驗(yàn)性的研究。所謂實(shí)驗(yàn)性研究是指，在其他變量被嚴(yán)格控制的情況下，給一部分研究對(duì)象一定量的咖啡，其他研究對(duì)象則得到一些無效對(duì)照劑。杜克大學(xué)的雷因表示，這樣的實(shí)驗(yàn)結(jié)果顯示，“實(shí)驗(yàn)性研究和觀察性研究對(duì)于咖啡因是否有益健康的結(jié)論截然不同?！?br>Still, many researchers believe that the only way to draw firm conclusions about something like coffee is through experimental trials in which some subjects are exposed to measured doses and others get a placebo, with other variables tightly controlled. When that's been done, says Duke's Dr. Lane, 'the experimental studies and the [observational] studies are in very sharp disagreement about whether caffeine is healthy or not.'
　　
咖啡的危害
Harmful Effects
　　
雷因所進(jìn)行的小規(guī)模對(duì)照研究顯示，對(duì)于那些已經(jīng)患有糖尿病的人來說,咖啡因──以藥片形式被精確分配──會(huì)提高餐后血壓和血糖水平。而其他研究則發(fā)現(xiàn)咖啡因加之壓力能夠更大幅度的提高血壓水平。“如果你是個(gè)正常的健康人，那么咖啡因或許不會(huì)產(chǎn)生什么長期影響，”雷因說?！安贿^有一些人預(yù)先已有患高血壓和心臟病的傾向，對(duì)這些人來講，咖啡因或許從長期來看是有害的?！?br>His own small, controlled studies have shown that caffeine-administered in precise doses in tablet form-raises blood pressure and blood-sugar levels after a meal in people who already have diabetes. Other studies have found that caffeine and stress combined can raise blood pressure even more significantly. 'If you are a normally healthy person, that might not have any long-term effect,' says Dr. Lane. 'But there are some groups of people who are predisposed to get high blood pressure and heart disease and for them, caffeine might be harmful over time.'
　　
流行病學(xué)家反駁說，這樣的小規(guī)模研究不能反映現(xiàn)實(shí)世界的情況，也無法衡量出患病的長期風(fēng)險(xiǎn)。
Epidemiologists counter that such small studies don't mirror real-world conditions, and they can't examine the long-term risk of disease.