A study that is in the news right now claims that people who drink two to three cups of coffee a day live longer than people who avoid coffee. So should we both drink two or three cups? Not necessarily. Let’s see where these numbers come from.
Two to three cups for longevity, maybe
this recent study taken from the UK Biobank, where the average age is 58, just over half of the participants are women and approximately 95% are white. On average, the researchers were able to follow the participants for 12 years after they answered a question about how much coffee they drink.
Looking at all-cause death, people who drank two to three cups of coffee a day had the lowest risk, and this applied whether they drank ground, instant or decaffeinated. For cardiovascular disease, those who drank one cup a day had the lowest risk, but for arrhythmia (irregular heartbeat), the sweet spot appeared to be four to five cups. In arrhythmia outcomes, decaffeinated coffee was no associated with a reduction in risk.
The study has many limitations, however, if you’re trying to use it to figure out how much coffee to drink. This group of middle-aged British people may not represent the rest of the world particularly well; and it’s not like people randomly decide how much coffee to drink. Income, social class and perceived health risks can all contribute to this choice, just to name a few (the British also tend to drink a lot instant coffee and espresso, result). The researchers also took people’s self-reported data at face value and assumed they drank the same amount of coffee over the years rather than continually reassessing.
Three to four cups for other health outcomes
A review published in the BMJ analyzed dozens of previous studies on coffee and concluded that people who drink coffee have a lower risk of cardiovascular disease, including strokes, some cancers, and some liver and gastrointestinal disorders. The amount of coffee associated with reduced risk was often in the range of three to four cups per day.
The author of this analysis said that people shouldn’t to start drinking coffee for these results, but that if you already drink coffee, “it can be part of a healthy diet.”
Part of the reason it’s so hard to figure out what’s wrong with coffee is that there are hundreds of different bioactive compounds in coffee, and caffeine is just one of them. The chemical profile can also be different depending on which beans you start with and how you brew the coffee.
But another reason is that these studies don’t randomly assign people as coffee drinkers or non-coffee drinkers; they usually just survey people about how much coffee they drink now to drink If your doctor has told you to limit caffeine because of, say, blood pressure, you’ll show up as a non-coffee drinker in the study. Therefore, people who avoid coffee may have different health-related risk factors than heavy drinkers, and this is not necessarily reflected in the study.
“A robust randomnessControlled trials are needed to understand whether the observed associations are causal [i.e., caused by coffee]”, the authors conclude.
Four cups or less, to be safe
The US Dietary Guidelines Just this to say about coffee consumption for non-pregnant adults: “For healthy adults, the FDA has cited 400 milligrams per day of caffeine as an amount not generally associated with dangerous negative effects.” (200 milligrams is the recommended limit during pregnancy.)
In other words, coffee is not so important for health that they recommend everyone to drink it. But it is not so dangerous that there is a hard limit. Instead, they name an amount that is basically fine. (Really huge amounts of caffeine would probably be bad. That’s a level they feel pretty safe saying it’s not a huge amount.)
So how much coffee is that? Most brewed coffee clocks in at about 100 milligrams per 8 fluid ounces. This varies quite a bit by brand and brewing style. For example, a 14-ounce Dunkin brewed coffee has 210 milligrams; a 16-ounce McDonald’s coffee has 145. You can look up the caffeine in your favorite beverage at Caffeine Informant.
One thing before you order: TThe guidelines also note that sweetened coffee drinks are one of the most common sources of added sugars in the diet. We need to keep added sugars below 10% of total calories, or about 50 grams. A Starbucks iced coffee has 20 grams; an F candyrappucino has 54. Black coffee, on the other hand, has basically none.