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Many people figure a few beers at a ballgame or a couple of glasses of wine with dinner won't put them over the legal limit for driving. But how alcohol affects people is highly individual, with a number of factors in the mix.
Quick shots of liquor hit the bloodstream faster than slow sips of wine. Drinking on an empty stomach impairs reflexes more than consuming alcohol with food. And women and older drinkers generally hit legal intoxication levels sooner than men and younger people.
Carbonated beverages raise alcohol levels faster, because the gas irritates the stomach lining, causing alcohol to be absorbed faster. (Sweet or caffeinated alcoholic drinks aren't absorbed any faster, it just seems that way because people often consume more of them than they realize.)
Many Asians have a genetic variation that gives them a flush and a very rapid heartbeat from even a small amount of alcohol.
And factors like fatigue, stress, illness and depression can magnify alcohol's impact.
Eileen Wolter was driving home from an office Christmas party she had organized in Los Angeles in 1998. 'I was definitely under a lot of stress,' she says. She had had several mixed drinks, a few glasses of wine and very little food, but thought she was fine -- until she took a turn too fast and hit a stop sign. She was driving with a flat tire and a broken wheel, causing even more car damage. A police car stopped to see if she was OK, and she flunked a breathalyzer test. 'I blew a 0.9,' says Ms. Wolter, who was arrested, fined $2,000 and sentenced to community service and alcohol education classes.
'I wasn't hurt -- just humiliated and angry and scared. Dealing with all of it -- and the fact that I could have hurt myself or someone else -- made me realize what a stupid chance I'd taken,' says Ms. Wolter, now a 40-year-old writer and mother of two who says she will never drink that way and drive again.
Drinkers who think they can tell when they've had enough are very often wrong. 'Alcohol can affect your reflexes even if you feel fine,' says Samir Zakhari, director of the division of metabolism and health effects at the National Institute of Alcohol Abuse and Alcoholism.
That's a key reason why many experts urge people who plan to drink any amount of alcohol not to drive, and vice versa.
In the U.S., it is illegal for adults to drive with a blood-alcohol concentration (BAC) at or above .08%, which represents the percentage of alcohol in the bloodstream. For drivers under 21, any alcohol in the blood is illegal.
The legal limit, once as high as .15% in some states, is now .08% in all 50 states. Some experts still consider it generous. Reaction time starts to slow at only half that amount, and much of the world sets stricter limits. It's .02% in China, .03% in most of India and .05% in much of Europe.
Many communities plan to join a nationwide crackdown on impaired driving between Aug. 19 and Sept. 11, including saturation patrols and sobriety checkpoints, especially during nighttime hours.
Such efforts have helped cut alcohol-related traffic deaths in the U.S. by almost 50% since 1980, though the number has plateaued in recent years at nearly 11,000 deaths annually, or one-third of all highway fatalities.
How does BAC work? One of the most important factors is how fast the alcohol is consumed, says Dr. Zakhari. It goes first to the stomach, then to the small intestine, where it is absorbed into the bloodstream and carried to the liver, where it is metabolized by liver enzymes.
'The liver can only break down the alcohol at the rate of about one drink per hour,' says Dr. Zakhari, who likens it to how fast a ticket-taker can let concert-goers through a gate.
Consuming one drink slowly over an entire hour is unlikely to make a person inebriated, he says. But drinking more than that amount, or the same amount faster, will overwhelm the liver. The excess alcohol 'goes into the bloodstream and every other organ in the body, including the brain,' he says.
Once that happens, only time can unwind the effects, Dr. Zakhari says. BAC generally falls by .015% per hour for both men and women -- but will rise again if you keep drinking. Drinking coffee, having a shower or splashing cold water on your face may make you feel more alert, but won't change your BAC.
Consuming food along with alcohol causes it to be absorbed more slowly, since a valve at the base of the stomach closes to allow for digestion before sending it along. Without this stop, the alcohol travels to the small intestine and into the liver faster.
What you eat along with the alcohol doesn't matter very much in terms of BAC. Fat, in, say, a marbled steak, slows the passage of food through the intestine, but only to a small extent. Likewise, drinking milk before consuming alcohol would have a negligible effect on blood levels.
Weight matters more than height, Dr. Zakhari says. A man who is 6-foot-4 and weighs 180 pounds will be as affected as a man who is 5-foot-4 and 180 pounds. But a man who is 6-foot-4 and 220 pounds will have a lower BAC after consuming the same amount. Women's bodies also tend to have less water than men's, which means the same amount of alcohol will yield an even higher BAC.
That was readily apparent at a recent dinner party, where guests were served alcohol and tested throughout the evening. A 110-pound woman, for example, reached a BAC of .079% with less than two drinks, while a 160-pound woman the same height had .05% on three.
Age matters, too. Older peoples' livers metabolize alcohol more slowly than younger people's. But excess alcohol can do more damage to young brains, since some portions are still developing, particularly those that govern impulse control and executive function.
Women's menstrual cycles are yet another factor: Alcohol metabolism increases about 10% right after ovulation.
People who drink heavily and regularly don't get as intoxicated as novice drinkers do on the same amount of alcohol, and tend to have a lower BAC because their livers eventually produce more of a particular enzyme (Cytochrome P450 IIE1) that breaks down alcohol more quickly.
But that may sometimes lull them into a dangerous complacency. Randy Strain, had just finished a stint with the Air Force, where off-duty drinking was common, in 2008 when he and his girlfriend were driving home on a rural road in Illinois after what he thinks were 'about 20 beers.' They were going about 80 miles per hour when they passed three police cars that were soon on his tail.
The ensuing 14 traffic violations and a DUI could have yielded a jail sentence, but a judge, noting his military service, only restricted his driver's license for six months, fined him $2,000 and ordered him to take 24 hours of classes.
Still, 'it was a life-changing experience,' says Mr. Strain, 27, of Oak Park, Ill. 'Now I go out max one night a week and take a cab home. I will not even get into a car if I or someone else has been drinking.'
參考譯文：
許多人認為，在看球賽時來上幾瓶啤酒或者在晚餐時小酌幾杯葡萄酒不會使體內的酒精含量超過駕駛者的法定酒精限度。但是，酒精對人體的影響有相當大的個體差異性，有很多因素會同時起作用。
和慢慢啜飲葡萄酒相比，快速飲酒會使酒精更快進入血液。與邊喝酒邊進食相比，空腹飲酒更容易使人反應變慢。女性和年長者通常比男性和年輕人更快達到法定醉酒水平。
在飲酒的同時喝碳酸飲料能加速酒精含量上升的速度，因為氣體會刺激胃粘膜，使酒精被人體更快地吸收。（甜酒或含咖啡因的酒精飲料被吸收的速度并不比其他酒快，只是看起來如此，因為人們通常會不知不覺地喝下過多這種飲料。）
許多亞洲人有一種基因變異現象，即使是少量酒精也會使他們臉紅以及心跳加速。
另外，疲勞、緊張、疾病和抑郁等因素也能擴大酒精的影響力。
1998年，艾琳•沃爾特(Eileen Wolter)在洛杉磯組織了一個辦公室圣誕派對，派對結束后，她驅車回家。她說：“我當時的壓力的確很大。”她喝了幾杯混合飲料和葡萄酒，幾乎沒怎么吃東西，但她認為自己的狀態還不錯，直到她發現自己拐彎速度過快，撞上了一個停車標志。在一個輪胎被弄癟、方向盤破損的情況下，她還在繼續駕駛，給汽車帶來了更嚴重的損壞。一輛警車停下來查看她的情況，她沒有通過酒精測試。沃爾特說：“通過呼氣測試，我的酒精含量是0.9。”她因此而被捕，并被處以2000美元罰款，被判參與社區服務和參加酒精教育班。
沃爾特說：“我沒有受傷，只是感到羞恥、生氣和驚恐。我面對的所有這一切──以及我有可能傷到自己或其他人的這個事實──讓我意識到這是一個多么愚蠢的冒險舉動。”現年40歲的沃爾特是一位作家和兩個孩子的母親，她說她再也不會那樣喝酒及駕駛了。
喝酒的人總認為他們能夠判斷自己是否喝多了，但他們往往是錯誤的。美國國立酒精濫用與酒精中毒研究所(National Institute of Alcohol Abuse and Alcoholism)新陳代謝和健康影響部門的主管薩默爾•扎克哈里(Samir Zakhari)說：“即使你感覺不錯，酒精也會影響你的反應速度。”
這正是許多專家強烈呼吁人們喝酒不開車、開車不喝酒的一個重要原因。
在美國，血液中的酒精濃度(BAC)達到或超過0.08%（也就是血液中的酒精含量百分比）的成年人駕車屬違法行為。對于21歲以下的駕駛員來說，只要血液中含有酒精就屬違法。
在美國的有些州，這個法定限度曾經高達0.15%，但現在所有50個州的法定限度都是0.08%。有些專家認為這個數字還是太高了。只要血液中的酒精含量達到這個法定限度的一半，人體的反應速度就會變慢。許多國家設定了更為嚴格的標準。中國是0.02%，印度的大部分地區是0.03%，歐洲的大部分地區是0.05%。
即將于8月19日至9月11日期間舉行的全美打擊危險駕駛行為的活動吸引了許多社團的加入，包括展開滲透式巡邏和設立飲酒駕車檢查點，尤其是在夜間。
自1980年以來，諸如此類的努力已經使美國和酒精有關的交通事故死亡人數減少了近50%，盡管最近幾年每年死于醉酒駕車的人數一直穩定在11,000人左右，占公路交通所有死亡事故的三分之一。
BAC受哪些因素影響呢？扎克哈里博士稱，最重要的一個因素就是喝酒的速度。酒精先到達胃部，然后是小腸，在這里被吸收到血液當中，然后被輸送到肝臟，被肝臟中的酶代謝出去。
扎克哈里博士稱，肝臟每小時只能分解一個標準飲酒量。他將其比作一個檢票員讓音樂會觀眾通過大門的速度。
他說，在一個小時的時間內慢慢喝下一個標準飲酒量不太可能讓人喝醉。但是，如果飲酒量超過這個標準或者以更快的速度喝下同樣多的酒將使酒精量超出肝臟的處理能力。多余的酒精會進入血液和身體的其他所有器官，包括大腦。
扎克哈里博士稱，一旦發生這種情況，只能靠時間來消除這些影響。BAC通常每小時會下降0.015%，對男人和女人來說都是如此，但是，如果你繼續飲酒，它還會再度升高。喝咖啡、淋浴或用冷水潑臉可能會使你感到更加清醒，但不會改變你的BAC。
在喝酒的同時吃一些食物會使酒精的吸收速度放慢，因為胃的底部有一個閥門，在你進食的時候會關閉，等食物消化之后才會打開，將其送入小腸。如果不經過這個停頓，酒精就會更快地進入小腸和肝臟。
你的下酒菜究竟是什么對你的BAC影響不是很大。脂肪（比如說一塊雪花牛排）會減緩食物通過腸道的速度，但影響程度很小。同樣，在飲酒前喝牛奶對BAC水平的影響也微乎其微。
扎克哈里博士稱，體重因素比身高因素重要。如果體重同為180磅，一個身高6英尺4英寸的男性和一個身高5英尺4英寸的男性對酒精的耐受力相同。但是，如果是一個身高6英尺4英寸、體重220磅的男性，在喝下同樣多的酒之后，他的BAC就會比較低。女性體內的含水量往往低于男性，這就意味著同樣多的飲酒量會使女性的BAC更高。
最近舉行的一場晚宴可以非常清楚地證明這一點。宴會整晚為嘉賓們提供酒精飲料并進行測試。例如，一位體重110磅的女性在喝下不到兩個標準飲酒量后，BAC達到了0.079%，而一位體重160磅的女性在喝下三個標準飲酒量后BAC才0.05%。
年齡也是一個影響因素。老年人的肝臟對酒精的代謝速度要比年輕人慢。但是，過多的酒精對年輕人大腦的損害更大，因為年輕人的一些大腦部位還在發育，尤其是那些管理沖動控制和執行功能的腦組織。
女性的月經周期是另一個影響因素：在剛剛排卵之后，酒精代謝會提高10%左右。
如果喝同樣多的酒，經常大量飲酒的人不會像剛開始飲酒的人那么容易醉，而且他們的BAC往往較低，因為他們的肝臟會釋放出更多的能更快地分解酒精的肝細胞色素P450 IIE1。
但這有時可能會讓他們陷入一種危險的自滿情緒。現年27歲、來自伊利諾伊州奧克帕克(Oak Park)的蘭迪•斯特蘭(Randy Strain)剛剛結束了在美國空軍(Air Force)的服役。空軍軍人們在輪休期間常常會去喝酒。2008年的一天，斯特蘭和女朋友在伊利諾伊州的一條鄉村公路上開車回家，據他回憶，他之前大概喝了20瓶啤酒。他們的時速達到80英里，超過了三輛警車，很快，這些警車就追上來了。
隨后斯特蘭被控14項交通違法行為和酒后駕車，這些指控本來會把他送進監獄，但一位法官注意到他在軍隊服役，便只是將他的駕照暫扣6個月，罰款2000美元以及下令他接受24小時的酒精學習班教育。
不過，斯特蘭說，這場經歷還是改變了他的生活。他說：“現在我每周最多只出去一個晚上，然后坐出租車回家。如果我或其他人喝了酒，我絕不會讓自己或他們開車。”
