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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.'
参考译文：
许多人认为，在看球赛时来上几瓶啤酒或者在晚餐时小酌几杯葡萄酒不会使体内的酒精含量超过驾驶者的法定酒精限度。但是，酒精对人体的影响有相当大的个体差异性，有很多因素会同时起作用。
和慢慢啜饮葡萄酒相比，快速饮酒会使酒精更快进入血液。与边喝酒边进食相比，空腹饮酒更容易使人反应变慢。女性和年长者通常比男性和年轻人更快达到法定醉酒水平。
在饮酒的同时喝碳酸饮料能加速酒精含量上升的速度，因为气体会刺激胃粘膜，使酒精被人体更快地吸收。（甜酒或含咖啡因的酒精饮料被吸收的速度并不比其他酒快，只是看起来如此，因为人们通常会不知不觉地喝下过多这种饮料。）
许多亚洲人有一种基因变异现象，即使是少量酒精也会使他们脸红以及心跳加速。
另外，疲劳、紧张、疾病和抑郁等因素也能扩大酒精的影响力。
1998年，艾琳•沃尔特(Eileen Wolter)在洛杉矶组织了一个办公室圣诞派对，派对结束后，她驱车回家。她说：“我当时的压力的确很大。”她喝了几杯混合饮料和葡萄酒，几乎没怎么吃东西，但她认为自己的状态还不错，直到她发现自己拐弯速度过快，撞上了一个停车标志。在一个轮胎被弄瘪、方向盘破损的情况下，她还在继续驾驶，给汽车带来了更严重的损坏。一辆警车停下来查看她的情况，她没有通过酒精测试。沃尔特说：“通过呼气测试，我的酒精含量是0.9。”她因此而被捕，并被处以2000美元罚款，被判参与社区服务和参加酒精教育班。
沃尔特说：“我没有受伤，只是感到羞耻、生气和惊恐。我面对的所有这一切──以及我有可能伤到自己或其他人的这个事实──让我意识到这是一个多么愚蠢的冒险举动。”现年40岁的沃尔特是一位作家和两个孩子的母亲，她说她再也不会那样喝酒及驾驶了。
喝酒的人总认为他们能够判断自己是否喝多了，但他们往往是错误的。美国国立酒精滥用与酒精中毒研究所(National Institute of Alcohol Abuse and Alcoholism)新陈代谢和健康影响部门的主管萨默尔•扎克哈里(Samir Zakhari)说：“即使你感觉不错，酒精也会影响你的反应速度。”
这正是许多专家强烈呼吁人们喝酒不开车、开车不喝酒的一个重要原因。
在美国，血液中的酒精浓度(BAC)达到或超过0.08%（也就是血液中的酒精含量百分比）的成年人驾车属违法行为。对于21岁以下的驾驶员来说，只要血液中含有酒精就属违法。
在美国的有些州，这个法定限度曾经高达0.15%，但现在所有50个州的法定限度都是0.08%。有些专家认为这个数字还是太高了。只要血液中的酒精含量达到这个法定限度的一半，人体的反应速度就会变慢。许多国家设定了更为严格的标准。中国是0.02%，印度的大部分地区是0.03%，欧洲的大部分地区是0.05%。
即将于8月19日至9月11日期间举行的全美打击危险驾驶行为的活动吸引了许多社团的加入，包括展开渗透式巡逻和设立饮酒驾车检查点，尤其是在夜间。
自1980年以来，诸如此类的努力已经使美国和酒精有关的交通事故死亡人数减少了近50%，尽管最近几年每年死于醉酒驾车的人数一直稳定在11,000人左右，占公路交通所有死亡事故的三分之一。
BAC受哪些因素影响呢？扎克哈里博士称，最重要的一个因素就是喝酒的速度。酒精先到达胃部，然后是小肠，在这里被吸收到血液当中，然后被输送到肝脏，被肝脏中的酶代谢出去。
扎克哈里博士称，肝脏每小时只能分解一个标准饮酒量。他将其比作一个检票员让音乐会观众通过大门的速度。
他说，在一个小时的时间内慢慢喝下一个标准饮酒量不太可能让人喝醉。但是，如果饮酒量超过这个标准或者以更快的速度喝下同样多的酒将使酒精量超出肝脏的处理能力。多余的酒精会进入血液和身体的其他所有器官，包括大脑。
扎克哈里博士称，一旦发生这种情况，只能靠时间来消除这些影响。BAC通常每小时会下降0.015%，对男人和女人来说都是如此，但是，如果你继续饮酒，它还会再度升高。喝咖啡、淋浴或用冷水泼脸可能会使你感到更加清醒，但不会改变你的BAC。
在喝酒的同时吃一些食物会使酒精的吸收速度放慢，因为胃的底部有一个阀门，在你进食的时候会关闭，等食物消化之后才会打开，将其送入小肠。如果不经过这个停顿，酒精就会更快地进入小肠和肝脏。
你的下酒菜究竟是什么对你的BAC影响不是很大。脂肪（比如说一块雪花牛排）会减缓食物通过肠道的速度，但影响程度很小。同样，在饮酒前喝牛奶对BAC水平的影响也微乎其微。
扎克哈里博士称，体重因素比身高因素重要。如果体重同为180磅，一个身高6英尺4英寸的男性和一个身高5英尺4英寸的男性对酒精的耐受力相同。但是，如果是一个身高6英尺4英寸、体重220磅的男性，在喝下同样多的酒之后，他的BAC就会比较低。女性体内的含水量往往低于男性，这就意味着同样多的饮酒量会使女性的BAC更高。
最近举行的一场晚宴可以非常清楚地证明这一点。宴会整晚为嘉宾们提供酒精饮料并进行测试。例如，一位体重110磅的女性在喝下不到两个标准饮酒量后，BAC达到了0.079%，而一位体重160磅的女性在喝下三个标准饮酒量后BAC才0.05%。
年龄也是一个影响因素。老年人的肝脏对酒精的代谢速度要比年轻人慢。但是，过多的酒精对年轻人大脑的损害更大，因为年轻人的一些大脑部位还在发育，尤其是那些管理冲动控制和执行功能的脑组织。
女性的月经周期是另一个影响因素：在刚刚排卵之后，酒精代谢会提高10%左右。
如果喝同样多的酒，经常大量饮酒的人不会像刚开始饮酒的人那么容易醉，而且他们的BAC往往较低，因为他们的肝脏会释放出更多的能更快地分解酒精的肝细胞色素P450 IIE1。
但这有时可能会让他们陷入一种危险的自满情绪。现年27岁、来自伊利诺伊州奥克帕克(Oak Park)的兰迪•斯特兰(Randy Strain)刚刚结束了在美国空军(Air Force)的服役。空军军人们在轮休期间常常会去喝酒。2008年的一天，斯特兰和女朋友在伊利诺伊州的一条乡村公路上开车回家，据他回忆，他之前大概喝了20瓶啤酒。他们的时速达到80英里，超过了三辆警车，很快，这些警车就追上来了。
随后斯特兰被控14项交通违法行为和酒后驾车，这些指控本来会把他送进监狱，但一位法官注意到他在军队服役，便只是将他的驾照暂扣6个月，罚款2000美元以及下令他接受24小时的酒精学习班教育。
不过，斯特兰说，这场经历还是改变了他的生活。他说：“现在我每周最多只出去一个晚上，然后坐出租车回家。如果我或其他人喝了酒，我绝不会让自己或他们开车。”
