Questions About Coffee and Health: We Have Some Answers
Q. and A.August 28, 2015
In an article on Monday, I reviewed the evidence behind coffee consumption and health in an effort to put to rest the idea that coffee is a “vice” or something we all need to cut back on.
We received many comments and questions from readers. In fact, we received so many that we thought it might be useful to respond to some of the most frequently discussed ones.
Are the same beneficial relationships seen with decaffeinated coffee?
Most studies did not include data on decaffeinated coffee, either because too few people drank it or because data were not available. The few studies that did, though, had differing results. With respect to cardiovascular disease, decaffeinated coffee did not seem to have the same protective effects as regular coffee. With respect to the one stroke meta-analysis, it seemed to be just as protective as regular coffee. In two breast canceranalyses, decaffeinated had the same nonrelationship as regular coffee. Decaffeinated coffee was also protective against lung cancer, not as protective against Parkinson’s disease, and protective against diabetes and overall mortality, but perhaps to a lesser extent than regular coffee.
But for most studies, there just aren’t data available. The conclusion to take away: There’s less evidence overall for a potential benefit, but still, there’s no evidence of harmful associations.
What constitutes a cup of coffee?
Pretty much all studies defined a cup of coffee as an 8-ounce serving. That’s smaller than what I imagine most people drink. A grande-size coffee at Starbucks (what is called simply “large” at most other coffee houses) is 16 ounces.
Are the same benefits seen with tea?
The literature on tea is about the same size as that for coffee, and reviewing it thoroughly would take more time than is appropriate for this column. However, a number of studies I reviewed did include tea in analyses, and those I can present here. People who drank more tea had a lower risk of Parkinson’s disease and of cognitive decline. Black tea had a potential protective effect against diabetes, but it was not statistically significant. Green tea had no relationship to the development of diabetes.
If we think there’s enough interest in tea, though, we could devote a future column to the evidence on that beverage.
Is the benefit from caffeine or from some other element in coffee?
It’s not known. I also don’t think it’s necessarily the same protective effect in each disease. I think that for many of the neurological issues, it could be caffeine acting as a stimulant in the brain. This hypothesis is supported by the fact that decaffeinated coffee doesn’t seem to be as protective, yet tea is. In some of the other diseases, though, the same benefits aren’t seen from other caffeine-containing beverages. No one is arguing that diet soda consumption is associated with less of a chance of getting cancer. Additionally, some protective effects are seen with decaffeinated coffee as well. It’s likely, therefore, that something else could be at work. We don’t know what, though.
What about high blood pressure or cholesterol?
A 2005 meta-analysis found that in randomized controlled trials caffeine was associated with an increase in blood pressure. When that caffeine was from coffee, however, the blood pressure effect was small. A 2011 study found that caffeine intake could raise blood pressure for at least three hours. Again, though, there wasn’t a significant relationship between long-term coffee consumption and higher blood pressure. A 2012 meta-analysis of 10 randomized controlled trials and five cohort studies could find no significant effect of coffee consumption on blood pressure or hypertension.
And, as has been reported in The New York Times, two studies have shown that drinking unfiltered coffee, like Turkish coffee, can lead to increases in serum cholesterol and triglycerides. But coffee that’s been through a paper filter seems to have had the cholesterol-raising agent, known as cafestol, removed.
High blood pressure and high cholesterol would be of concern because they can lead to heart disease or death. Drinking coffee is associated with better outcomes in those areas, and that’s what really matters.
Some readers were upset that I neglected to mention some of the deleterious effects of caffeine. What about jitteriness and mood changes?
I want to reiterate that the point of the piece was not to tell people to drink coffee. As I said in my recent article on food recommendations, I don’t think there is much value in preaching or judging what others eat or drink. Moreover, this evidence is epidemiologic, that is, based on observations of patterns. I don’t want to fall prey to the mistake of recommending we change our eating behavior without evidence from randomized controlled trials.
The point of the article was to show that there’s no evidence that coffee is bad for the average person. Data do not support the idea that we are drinking “too much.” Coffee does not appear to be associated with poor health outcomes — the opposite is true. In light of this, we should stop telling everyone to avoid it, or judging others for drinking it. We should also stop feeling guilty or feel we need to consume less.
That is, unless it’s not making you feel well. As I also said before, individual trial and error is likely necessary when it comes to nutrition. Some people need to avoid caffeine for medical reasons, and they should. If coffee makes you feel bad, or makes it hard for you to sleep, or renders you a less likable person — then by all means feel free to cut back or stop.
But if you like it, then by all means enjoy it.
咖啡與健康那些事兒
新知2015年8月28日
Heather Walsh for The New York Times
使用Chemex沖煮法(Chemex pour-over method)製作咖啡。
有人認為喝咖啡是一種「壞習慣」，需要努力改正。在周一的一篇文章中，我綜述了有關喝咖啡與健康的證據，以期澄清這些誤解。
對此，讀者們發表了很多評論，也提出了不少問題。於是，我們決定從中挑出一些最有代表性的問題作答，或許能對大家有所助益。
飲用無咖啡因咖啡對健康也同樣有益么？
大多數研究都沒有納入無咖啡因咖啡的數據，這或許是因為喝這種咖啡的人太少，也可能是因為拿不到相關的數據。僅有少數研究納入了此類咖啡的數據，但並沒有得出一致的結果。無咖啡因咖啡似乎不像普通咖啡那樣可以預防心血管疾病。一項關於中風的薈萃分析則表明，無咖啡因咖啡與普通咖啡一樣具有預防效果。兩項針對乳腺癌的分析顯示，無咖啡因咖啡與普通咖啡均無甚作用。無咖啡因咖啡也能預防肺癌，但對帕金森氏症沒什麼效果；在預防糖尿病並降低整體死亡率方面，無咖啡因咖啡有一定的作用，但或許比正常咖啡稍弱。
但大多數的研究都缺乏相關數據。我們的結論是：總體而言，能證明無咖啡因咖啡潛在效益的證據較少，不過，也沒有證據表明它有害。
一杯咖啡指的是多大容量？
幾乎所有的研究都將一杯咖啡定義為8盎司（約合227克）的一份。我想這大概比大多數人平時喝的一杯要少些。星巴克(Starbucks)里的大杯(grande-size)咖啡是16盎司（約合454克）。
喝茶也像喝咖啡同樣有益么？
有關茶的文獻與關於咖啡的同樣多，要將它們徹底查閱一番需要耗費很多時間，就本專欄而言似乎無需如此大費周章。不過，在我之前綜述的研究中有一些確實也將茶納入了分析，下面我就簡單地介紹一下。喝茶較多的人患帕金森氏症以及認知功能減退的風險均較低。紅茶或可預防糖尿病，但其不具備統計學顯著性意義。綠茶與糖尿病的發生無相關性。
然而，如果有很多人都對茶感興趣的話，我們可以在未來的某一期專欄里討論關於該飲料的科學證據。
喝咖啡有益健康，是因為咖啡因還是咖啡中含有的其它成分的緣故？
目前還不清楚。我認為，對不同疾病起預防作用的成分未必相同。比如，對於神經系統上的許多問題，可能是咖啡因在發揮大腦興奮劑的作用。我的這個假設是有事實依據的：咖啡和茶都可以預防這些問題，而無咖啡因咖啡卻無此功效。但是，對於別的一些疾病，飲用其它含咖啡因的飲料卻未顯示出同樣的效益。從沒有人提出飲用無糖汽水與患癌症的幾率減少相關。此外，無咖啡因咖啡也同樣可以預防某些疾病。因此，很可能還有別的東西在起作用，只不過我們還沒有明確那具體是什麼。
那麼，喝咖啡對高血壓或膽固醇有什麼影響么？
2005年的一項薈萃分析發現，在隨機對照試驗中，咖啡因與血壓升高相關。但是，當咖啡因來源於咖啡時，對血壓的影響卻很小。2011年的一項研究發現，攝入咖啡因的升血壓效果至少可持續三個小時。但長期飲用咖啡與較高的血壓之間依舊沒有顯著相關性。2012年的一項薈萃分析納入了10項隨機對照試驗和五項隊列研究，結果發現飲用咖啡對血壓或高血壓並無顯著影響。
但是，正如《紐約時報》雜誌(The New York Times)曾經報道的，有兩項研究表明，飲用未過濾咖啡（如土耳其咖啡）可導致血清膽固醇和甘油三酯增加。但是，用濾紙過濾咖啡似乎可以去除掉升膽固醇的物質——咖啡醇。
高血壓和高膽固醇會引起人們的重視，是因為它們會導致心臟病甚至死亡。而喝咖啡對這些問題都有益處，這才是問題的關鍵所在。
我忘了提及咖啡因的有害影響，這讓一部分讀者感到不滿。那麼，喝咖啡與神經過敏和情緒變化之間有什麼樣的關係？
我想重申的是，本文的論點並非是要勸告大家都去喝咖啡。正如我在最近的一篇關於飲食建議的文章中所說，我認為對別人的食物和飲料指指點點說教評判沒什麼意義。而且，以上提出的都是流行病學證據，也就是說，它們都是從觀測研究中發現的模式。在獲得來自隨機對照試驗的證據之前，我可不想輕易建議大家改變當前的飲食行為，因為這種建議有可能是錯誤的。
本文只是想要指出，尚無證據表明咖啡對普通人有害。有人覺得我們喝咖啡「過多」，但現有數據並不支持這一觀點。咖啡與損害健康無相關性——事實上，恰恰相反。有鑒於此，我們不應該再阻止大家喝咖啡，或者對喝咖啡的人指手畫腳，也無需再因為自己愛喝咖啡而感到羞愧或者認為自己應該克制。
當然，要是喝咖啡會讓你感覺不舒服就另當別論了。我之前也說過，在涉及到營養問題時，可能有必要根據個人的具體情況來一番試錯。有些人因為醫學上的原因不能攝入咖啡因，那麼他們就不應該喝咖啡。如果喝咖啡會讓你感覺不舒服，令你難以入睡，或者會讓你變成一個不太討人喜歡的人，那麼，你也盡可以少喝或者不喝咖啡。
但是，如果你喜歡咖啡，那就隨心所欲地享用吧。
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