There is a persistent belief that drinking coffee is bad for you. Some alternative medicine systems eschew all coffee drinking (but are enthusiastic about coffee enemas). Certainly if you overindulge the sleeplessness and tremors will remind you of the perils of too much of a good thing. But there is a longstanding belief that long term consumption of coffee is in some nebulous way “bad”. This is despite coffee being packed with the sorts of antioxidants you would pay good money for at the health food store.
Now a new study suggests that people who drink coffee are less likely to die.
Wow! Great! I’ll just fire up the espresso machine then.
Hold on, firstly, the effect is modest, you are around 10% less likely to die if you are drinking 6 or more cups of coffee a day. Secondly, it’s an association. We don’t know if it’s the coffee drinking leading to less death, or something else which coffee drinkers are more likely to do.
Oh, so I should pack the espresso machine away.
No, there is now a fair bit of evidence that modest coffee consumption can give you some degree of protection against things like Parkinson’s Disease and Alzheimer’s disease (again though, we don’t know if it’s coffee per se that gives protection, or something else that coffee drinkers do). And coffee tastes good too.
But the apparent health benefits of any food or beverage should not be an excuse to overindulge, like the people who use the reported benefits of drinking modest amounts of red wine as an excuse to drink bottles of the stuff in one go.
So while I get the espresso going, what is the latest evidence?
A research team followed a group of nearly 400,000 people for 14 years, or until they died ( whichever came first). They gave the people extensive questionnaires about coffee drinking, food consumption, lifestyle and measured a range of health parameters at the start of of the study. Then after the 14 years they looked at the death rates in coffee drinkers and non-coffee drinkers.
They found that more coffee drinkers died.
That’s the problem with looking at these sorts of studies simplistically. There are a whole other bunch of factors that influence death rates. In epidemiology speak these are called “confounders” (because They confound interpretation). It turns out that most coffee drinkers also smoke, so the increased death rate was due too smoking differences between coffee and non-coffee drinkers.
If the researchers had not measured smoking rates in the people, they would have been fooled into thinking that coffee was bad for you. This is also why we say that the coffee drinking - less death is just an association, the increased life-span could be due to something that wasn’t measured, even though lots of things were measured.
So how did they work out coffee drinking was good for you?
In epidemiology speak they “ controlled for the confounders”. If you compare just smokers who don’t drink coffee with those that do, coffee drinking smokers livers longer than non-coffee drinking smokers. Of course, it’s not quite as simple as that. When you have a lot of measurements you have to do some clever mathematics to sort it all out.
So is it a good study?
Yes, they had a big group of people they followed for a sufficiently long time, they only looked at people who were reasonably healthy when they started following them (so disease progress patterns couldn’t mess things up) and they measured a heck of a lot of lifestyle factors.
One problem is, as the researchers point out themselves, that they only asked people about their coffee consumption at the beginning of the study. So they had no way of knowing if people decreased or increased their consumption, or switched to or from decaf.
Another thing they didn’t measure was the type of coffee, apart from crudely separating caffeinated from non-caffeinated. So we have no way of knowing if most people were drinking Floor-Sweepings brand instant coffee or Heart Burtser double espressos.
The latter information is important if we want to generalise to other populations. US coffee as generally consumed is somewhat different in strength to how the Europeans take it. I vividly remember visiting a friend of mine in Seattle. At the time I was working as a postdoctoral student in Berlin. There was an industrial strength filter coffee machine outside my lab door, pumping out vicious black heart starters almost 24/7. My mate proudly took me to the street in Seattle where he claimed the best coffee in the US was served.
It tasted like pinkelwasser. That is not a compliment.
Sounds uninspiring, so how is coffee making people live longer?
We know how it’s not doing it. It’s not caffeine, as decaffeinated and caffeinated coffee had pretty much the same effect (except for injuries and accident, where caffeinated coffee was a clear winner).
Coffee is chock full of antioxidant chemicals such as polyphenols and Chlorogenic acid. We know that people who consume foods rich in antioxidants have better health outcomes and live longer than people who don’t. We also know that feeding people pure antioxidant vitamins is a waste of time. The antioxidant status of food may be unrelated to health, but may be a marker for something else in these foods.
So whether it’s the antioxidants in coffee is unclear. This hasn’t stopped companies from adding extra antioxidants to instant coffee though (although they were doing this well before this study came out). Maybe it’s something completely unrelated, like coffee drinkers are more likely to walk to their local coffee shop, getting a bit more exercise.
So if I want to live longer?
Choose you parents carefully, eat plenty of fresh fruit and vegetables, get more exercise, develop or participate in social networks. Why not walk down to your local coffee shop and share a cappuccino with your friends?
Milk and two sugars please.