咖啡因是世界上用得最多的兴奋剂——从好的方面看，咖啡因让人集中注意力、保持工作状态，也是精力焕发的能量来源。
我们欧美人大都喝咖啡来提神。（译注：亚洲人喝茶）
也许是因为咖啡给人一种依赖品的感觉，我们常常担心喝咖啡是否会过量，甚至想完全戒掉咖啡。
咖啡因确实容易过量——重度咖啡饮用者咖啡因摄入量高于推荐的每天400毫克。咖啡因摄入过量，尤其是摄入过快会导致失眠、焦躁、心跳加快。
但是，绝大部分针对咖啡的研究都表明咖啡对健康不但无害，且有益。
通常，我们不能说喝咖啡就一定健康——因果机制尚不明朗。但研究结果确实表明喝咖啡的人患某些疾病的风险较低。
有些食物和饮料的确应该少吃少喝，但咖啡不应该在这个清单上，以下是原因。
肝健康：综合九个研究结果发现，喝咖啡可降低肝硬化风险。
报告中说，一天喝一杯咖啡可以降低22%患肝硬化的风险，肝硬化主要由酗酒导致。一天喝两杯可降低43%，三杯降低57%，四杯降低65%。
来源：Alimentary Pharmacology and Therapeutics（营养药理与治疗学杂志）
心脏病：通过分析两百份研究的报告发现，一天喝3-4杯咖啡的人可降低 19% 患心血管疾病的风险。
来源：BMJ （英国医学杂志）
二型糖尿病：一项大型的研究报告发现，每天多喝的一杯咖啡可降低7%发展成二型糖尿病的风险。
来源：JAMA Internal Medicine（美国医学会杂志·内科学）
癌症：一项研究报告发现，重度咖啡饮用者（每天至少喝三杯）患癌风险可降低18%。
另一份报告说，每天至少喝一杯咖啡患肝癌的风险可降低15%，患子宫内膜癌的风险可降低8%。
一些数据还表明，喝咖啡的人不太容易患口腔癌和晚期前列腺癌。
来源：European Journal of Cancer Prevention,BMJ（欧洲癌症预防杂志，英国医学杂志）
阿尔兹海默症和老年痴呆：一个关于咖啡摄入与脑健康的综合分析研究估测，喝咖啡的人患阿尔兹海默症、老年痴呆、认知能力衰退比不喝的人低16%。
也有一些较小规模的研究表明喝咖啡可以更大程度上降低患阿尔兹海默症风险。
来源：Journal of Alzheimer's Disease,European Journal of Neurology （阿兹海默症期刊，欧洲神经学杂志）
抑郁症：通过对5万名女性的研究表明，一周至少喝一杯咖啡可降低15%患抑郁症的风险，而每天喝2-3杯则可降低20%。
通过对超过10万人的研究发现，喝咖啡的人自杀的可能性比不喝的人低45%，重度咖啡饮用者（每天4杯以上）自杀的可能性比不喝的人低53%。
来源：JAMA Internal Medicine,The World Journal of Biological Psychiatry （美国医学会杂志·内科学，世界生物精神病学期刊）
较低的死亡率：通过跟踪50万欧洲人16年的研究发现，每天喝3杯以上咖啡的男性死亡率比不喝的男性低12%，同样条件下，女性死亡率则低7%。
值得注意的是，经常喝咖啡更不容易死于循环系统和消化系统疾病。重度咖啡饮用者的肝脏更健康。
另一个针对185855名美国人的研究证实了这个结果。每天喝一杯咖啡可降低12%的死亡率，喝2-3杯则可降低18%早逝的可能性。（脱咖啡因的咖啡也有同样的效果）
8 ways that drinking coffee is connected to better health and a longer life
Caffeine is the most commonly used psychoactive drug in the world — for good reason. It wakes us up, helps us stay on task, and provides an oft-needed energy boost.
And most of us in the Americas and Europe get our caffeine fix from coffee.
But people often worry that they should limit their coffee consumption or cut it out completely. That's probably because coffee can feel like a crutch.
It is possible to overdo it on caffeine —many heavy coffee drinkers surpass the recommended limit of 400 mg of caffeine per day, and that can cause insomnia, restlessness, or a fast heartbeat, especially if consumed too fast.
But most research on coffee consumption indicates that coffee is not bad for us, and is associated with some pretty impressive health benefits.
In most cases we can't say that coffee actually causes health benefits — the causal mechanism is unclear. But research does suggest that coffee drinkers are less likely to suffer from certain illnesses.
There are plenty of foods and drinks that most of us should consume less. But here's why coffee shouldn't be on that list.
Liver health: A review that combined the results of nine studies found that drinking more coffee is associated with lower risk for cirrhosis.
In the review, drinking one cup of coffee per day was shown to be linked with a 22% reduced risk for cirrhosis, a liver disease that is often caused by heavy alcohol consumption. Two daily cups were associated with a 43% reduced risk, three cups with 57% reduced risk, and four cups with 65% reduced risk.
Source:Alimentary Pharmacology and Therapeutics
Heart disease: A review of more than 200 studies found that people who drank three or four cups of coffee per day were 19% less likely to die from cardiovascular disease.
Source:BMJ
Type 2 diabetes: One large review of studies found that every additional cup of coffee one drinks per day was correlated with a 7% reduced risk for developing Type 2 diabetes.
Source:JAMA Internal Medicine
Cancer: One review found that heavy coffee drinkers (who had at least three cups a day) had an 18% reduced risk for cancer.
Another review found that at least one cup each day was associated with 15% reduced risk for liver cancer and an 8% reduced risk for endometrial cancer.
Some data indicates that coffee drinkers may be less likely to suffer from oral/pharyngeal cancer and advanced prostate cancer as well.
Source:European Journal of Cancer Prevention,BMJ
Alzheimer's disease and dementia: A meta-analysis of studies about coffee intake and brain health calculated that regular coffee drinkers were approximately 16% less likely to suffer from Alzheimer's, dementia, or cognitive decline.
There are smaller studies that suggest drinking coffee can lead to even bigger risk reductions for Alzheimer's.
Source:Journal of Alzheimer's Disease,European Journal of Neurology
Depression: One large study of more than 50,000 women showed that drinking at least a cup of coffee each week was associated with 15% reduced risk for depression, and drinking two to three cups per day was associated with 20% reduced risk.
Another study that looked at more than 100,000 men and women found that coffee drinkers were 45% less likely to die from suicide and heavy coffee drinkers (four or more cups a day) 53% less likely to die from suicide.
Source:JAMA Internal Medicine,The World Journal of Biological Psychiatry
Overall mortality: One large study of more than 500,000 European people found that in a 16-year-period, men who drank three or more cups per day were 12% less likely to die, and women 7% less likely to die.
In particular, people were less likely to diefrom circulatory and digestive diseases. Heavy coffee drinkers also had healthier livers.
Another study of 185,855 Americans confirmed that result. People who drank one cup per day were 12% less likely to die. Two to three cups were associated with an 18% decrease in risk for early death. (Decaf had the same benefits.)
