Among the most frequently asked questions I get is about
caffeine. Is it safe? How much is okay? Is it the newest health food? I’d like to answer a lot of these questions right now. It’s also the topic of this week’s
Today Show segment:
What is caffeine, and where does it come from? 
Caffeine is naturally-occurring in many plants, and found in the leaves, seeds, and/or fruits of more than 60 plant types. The most common sources are coffee beans, cocoa beans, and kola nuts. Caffeine is a stimulant, and has numerous positive nervous system effects, including fighting fatigue and improving mental alertness and focus, and increasing athletic performance.
Is caffeine safe to consume? Thousands of studies have been done testing caffeine’s safety. In a word: Yes. Studies repeatedly demonstrate that
caffeine is safe and effective with moderate intake (defined as 300 mg per day–see below for caffeine content of drinks) and does not cause any ill effects in healthy adults (and children). Some people who are “caffeine sensitive”–like people with high blood pressure and the elderly–may need to consume less to avoid negative effects like rapid heart beat, stomach upset, sleeplessness or an increase in blood pressure.
How much caffeine is found in food and drinks? These amounts are approximate, and can vary depending on size, and method of preparation. But, they are a good rule of thumb to guide you:
Coffee/Tea/Soda: | 10 oz. mug of black coffee | 100 mg |
| 1 shot (1 oz.) of espresso | 50 mg |
| 10 oz. mug of tea | 50 mg |
| 12 oz. can of soda | 40 mg |
Chocolate Products: | chocolate milk/cocoa | 5 mg |
| 1 oz. milk chocolate | 5 mg |
| 1 oz. dark chocolate | 20 mg |
Energy Drinks (Some examples of many on the market):
| 2.5 oz. UpShot | 200 mg |
| 16 oz. Rock Star | 160 mg |
| 8.3 oz. Red Bull | 80 mg |
Energy “Pills” | 1 pill Max. Strength No Doz | 200 mg |
What about other health benefits? While most of us are familiar (and seek out) the stimulant properties of caffeine, there are other
positive health aspects to consider. While these are just associations–observed in large population studies comparing health risk and caffeine intake–they suggest that the actions of caffeine are more widespread.
These actions include a reduction in the risk of type 2 diabetes, Parkinson’s disease, some liver diseases, and colorectal cancer. So, don’t start drinking coffee as a “health food," but these may be some “value added” factors you didn’t know about!
Aren’t there a lot of negative effects caffeine can have? 
Some negative effects can occur for some people, in amounts usually over 300 mg/day, or a single higher dose of over 200 mg. You may need to experiment yourself to know best: Remember to calculate both the amount of caffeine you have in a specific drink, as well as the total consumed all day.
For
women with low calcium intake, too much caffeine might contribute to bone loss. Interrupted sleep can occur, as can reflux and stomach upset. An increase in blood pressure can occur in some people as well. Some people report nervousness, and a more rapid heartbeat.
Check with your doctor if you sense some negative effects associated with your caffeine intake.
Are coffee and tea different from caffeine in their reported actions? Coffee and tea, while containing caffeine, also contain many
health-promoting antioxidants. While consuming coffee or tea for their health benefits is not recommended, if you’re a coffee or tea drinker, doing so in moderation might contribute to your overall good health.
Watch this Street Talk clip where we asked people on the street "
How many cups of coffee do you drink a day?"
Please weigh with any comments or questions on your mind!
译文:
有关咖啡因的新发现
人们最常问我的问题是关于咖啡因的：它安全吗？摄入量多少合适？最新发现它是健康食物，对吗？――在此我将回答大部分的此类问题。这也是本周的“今日秀”栏目的话题。
咖啡因为何物？从何而来？
咖啡因是一种天然物质，普遍存在于６０多种植物的叶片、种籽以及/或果实中。其最常见的来源为咖啡豆，可可豆以及可乐果。咖啡因是一种刺激剂，对神经系统有众多积极作用，其作用之一就是消除疲劳，提神醒脑，以及提高运动技能。
摄入咖啡因安全吗？
数以千计的研究结果都证明了咖啡因是安全的。总之，没问题。研究一再证明，在正常摄取量以内的咖啡因安全有效（所谓正常摄取量是指每日300毫克，详情见下表），对大人以及儿童都不会有任何副作用。某些对咖啡因敏感的人群，比如说高血压患者或老人，则应酌情减少摄入，以避免心跳加速，胃部不适，失眠或者血压升高等症状。
食品饮料中咖啡因的含量为多少？
下表中注明的含量为近似值，根据调配方法以及成分多少有所变化。当然，这些数据可供你大致估摸一下：
咖啡/茶/汽水 | 10盎司. 一杯黑咖啡 | 100毫克 |
| 1 杯(1盎司.)一倍比例的意大利特浓咖啡 | 50毫克 |
| 10盎司.一壶茶 | 50毫克 |
| 12盎司一罐汽水 | 40毫克 |
巧克力制品：: | 巧克力奶/可可 | 5毫克 |
| 1盎司. 牛奶巧克力 | 5毫克 |
| 1盎司. 黑巧克力 | 20毫克 |
功能饮料 (现例举市面上常见的几种): | 2.5盎司. UpShot | 200毫克 |
| 16盎司. Rock Star | 160毫克 |
| 8.3盎司. 红牛 | 80毫克 |
提神药片 | 1 片 Max. Strength No Doz | 200毫克 |
还有其他健康方面的好处吗？
我们大部分人都知道咖啡因提神的作用，也正是冲这个去的。但我们也应该了解，它在其他方面也有益健康。将健康
风险和其摄入量相比较的有关研究涉及了大量人群，其结果显示，咖啡因的良性作用相当广泛。――当然，上述结论只是推断。
这些良性作用包括降低患二型糖尿病，帕金森症，某些肝脏疾病以及大肠癌的患病危险。如此看来，不需要开始把咖啡当“健康食品”服用，但是了解了原来不知道的“增值服务”，也挺不错的。
咖啡因有许多副作用，不是吗？
对某些人群而言，如果摄入量常超过每天300毫克，或者一次摄入量超过200，咖啡因就可能有副作用。你可能需要亲自体验一下来发现最佳摄入量：别忘了统计你在某饮品中的具体摄入量以及一天的消耗总量。
对于钙摄取缺乏的女性，过量咖啡因将导致钙质流失和骨质疏松。同时可能出现的症状还会有易惊醒，反胃以及胃部灼烧不适。对于某些人来说可能会出现血压升高的症状。有些人称他们会感觉精神紧张，以及心跳加速。
如果你觉得摄入咖啡因带来一些不适症状，请咨询你的医生。
咖啡和茶是否与咖啡因在其疗效方面有所不同？
咖啡和茶均含有咖啡因，也含有诸多促进健康的抗氧化剂。我们不建议人们为了追求健康喝咖啡或茶，但是如果你是一个咖啡爱好者或者茶迷，适量饮用可能对你的健康有益。
欢迎你收看接下来的街头采访片段，在该片段里，我们询问路人: “您一天喝多少杯咖啡？”
如有任何评论和疑问，请自行好好思考吧。