Coffee drinkers, rejoice. Two new studies are linking our favourite hot beverage to a decreased chance of being killed by heart disease, cancer or a stroke. So, does this mean we can start drinking coffee with reckless abandon? We spoke to the experts to find out, and not surprisingly, the answer is complicated.
Image: Steve Snodgrass/Flickr
People who drink coffee appear to live longer, according to a pair of studies published today in the Annals of Internal Medicine. The studies -- which involved hundreds of thousands of participants across a diverse set of ethnic groups -- showed that folks who drink at least one cup of coffee a day were 12 per cent less likely to die of diseases such as heart disease and cancer. This effect jumped to 18 per cent among people who consumed two to three cups per day. Importantly, these associations held true for participants who drank either caffeinated or decaffeinated coffee, which would seem to imply that caffeine has nothing to do with it.
But to say that these studies close the case on coffee, so to speak, would be taking it too far. The researchers weren't able to identify a causal relationship, nor were they able to explain why coffee appears to confer these health benefits. And importantly, some experts are challenging the conclusions reached in these two studies, saying the results were misleading, and that blanket statements about coffee consumption ignore the fact that, for some, caffeine is dangerous.
Regardless, the new studies offer substantial findings given the stigma associated with coffee consumption, and the fact that an estimated 2.25 billion cups of this delicious beverage are consumed each day around the world. Coffee has previously been linked to bladder cancer, increases in the risk of heart disease, stomach ulcers and heartburn -- yet little evidence exists to support these largely debunked claims.
And in fact, quite the opposite appears to be the case. One recent meta-study linked coffee consumption to a reduced risk of liver and uterine cancer. Evidence is also mounting that coffee may protect against heart disease, type 2 diabetes and Parkinson's. These findings sure seem promising, but sceptics have argued the jury's still out on coffee, pointing to deficiencies in the research methods, such as a focus on specific ethnicities, or failing to follow-up with study participants. The two new analyses provide some of the most compelling evidence yet in support of coffee's purported health aspects.
In the first study, a research team from the University of Southern California found that higher coffee consumption was linked to lower risk for death in both white and non-white populations -- an important finding given that different ethnicities have different lifestyles and disease risks. Coffee consumption amounting to two to three cups a day, for example, was associated with a reduced risk of death due to heart disease (21 per cent decrease), cancer (eight per cent decrease), stroke (27 per cent decrease), diabetes (23 per cent) and respiratory (10 per cent) and kidney disease (41 per cent).
Crucially, these findings were generalisable across cultures, including African-Americans, Japanese-Americans, Native Hawaiians, Latinos and whites. Health effects were observed in all of ethnicities studied.
Data came from the Multiethnic Cohort Study, a collaborative effort between the University of Hawaii Cancer Center and the Keck School of Medicine that involves more than 215,000 participants. Every five years, participants fill out questionnaires about their diet and lifestyle, along with family and personal medical history information. The average follow-up period is 16 years. When analysing the data, the USC researchers adjusted for age, sex, ethnicity, smoking habits, education, pre-existing disease, physical exercise and alcohol consumption.
"This study is the largest of its kind and includes minorities who have very different lifestyles," said Veronica Setiawan, lead author of the study, in a statement. "Seeing a similar pattern across different populations gives stronger biological backing to the argument that coffee is good for you whether you are white, African-American, Latino or Asian."
Among coffee drinkers, reduced mortality rates were present regardless of whether participants drank caffeinated or decaffeinated coffee. So, whatever is causing the added longevity appears to have nothing to do with caffeine.
Crucially, the USC researchers aren't saying that coffee prolongs life, just that an association has been found between coffee consumption and longevity. Correlation does not necessarily imply causation, and the study didn't point to any chemicals or compounds in coffee that explain these health effects. Still, according to Setiawan, "it is clear that coffee can be incorporated into a healthy diet and lifestyle."
In the second study, researchers from the Imperial College London and International Agency for Research on Cancer (IARC) came to similar conclusions, though using a different subset of participants. In the largest study of its kind, the scientists analysed survey data from more than half a million people across 10 European countries, and found that people who drink around three cups a day tend to live longer than non-coffee drinkers. They found coffee drinkers to have a reduced risk of death from all causes of mortality, including circulatory diseases and diseases related to the digestive tract. And like the other study, decaf drinkers saw these reduced mortality rates just as much as folks drinking regular coffee.
For the study, the ICL and IARC researchers looked at data from the EPIC study (European Prospective Investigation into Cancer and Nutrition), which included 521,330 people over the age of 35. Diets were assessed with questionnaires and interviews, and again, the researchers controlled for factors such as diet and smoking (interestingly, people who drank more coffee were more likely to be younger, smokers and regular alcohol drinkers). After 16 years of follow-up, nearly 42,000 people who had enrolled in the study had passed away, dying from a range of conditions, including cancer, circulatory diseases, heart failure and stroke.
"We found that drinking more coffee was associated with a more favourable liver function profile and immune response," explained lead author Marc Gunter. He added: "Due to the limitations of observational research, we are not at the stage of recommending people to drink more or less coffee. That said, our results suggest that moderate coffee drinking -- up to around three cups per day -- is not detrimental to your health, and that incorporating coffee into your diet could have health benefits."
Miriam Nelson, Director of the Sustainability Institute at the University of New Hampshire, is excited by these findings, and says these two studies are bigger and more diverse than previous investigations. Nelson, who wasn't involved in either study, was impressed by the length of the follow-ups, the size of the cohorts, and the cross-cultural examination. Yet she emphasised that there are still many things these studies don't tell us.
"We still don't understand how high coffee consumption affects pregnancy, and we don't know what high coffee consumption does to children," Nelson told Gizmodo. She says it's still inappropriate to give coffee to children, adding that there's very little doubt that coffee affects our sleep, at least for some individuals. People who drink a ton of coffee, and who have serious sleep issues, may want to take the new findings with a grain of salt.
Then, of course, there's all that crap we put into our coffee.
"If you enjoy coffee, then feel free to drink it, perhaps even three to five cups a day," said Nelson. "Coffee has health benefits, but we need to be wary of adding extra calories with sugar and cream. We need to be smart."
But Paolo Palatini, Head Vascular Medicine at Italy's University of Padova, was profoundly unimpressed with the new research. "After reading the papers I was horrified about how these articles... are cursory and biased," he told Gizmodo. "As soon as they are published I will write a letter to the editor [of The Annals of Internal Medicine] to express my criticisms." In a word, he thinks the studies are misleading.
"In the papers the authors did not discuss the issue of the different types of coffee that may have different impact on outcomes," he said. "In the European study they evaluated coffee in milliliters which is absurd because in Italy cups contain 30-40 ml of concentrated coffee whereas in most European countries cups are much larger. This minimized the effect of Espresso coffee which may be deleterious compared to others."
He says the groups of coffee drinkers surveyed in both studies were unbalanced, the most significant imbalance being the large percentage of smokers among the heavy coffee drinkers. "Results for coffee subgroups differ in the two studies, and adjustment for smoking can hardly be applied," he said. "At any rate, the two studies demonstrate that coffee drinkers also are smokers which is very deleterious for health, and this aspect is completely neglected by the authors."
Palatini also doesn't buy the idea that caffeine has no effect on health outcomes, pointing to his own research showing the importance of caffeine metabolism on cardiovascular disease, and how genetics plays a critical role. He's also shocked that none of the researchers referenced an Italian study showing the negative effects of coffee on cardiovascular outcomes -- an omission Palatini says was done "on purpose" and is "unacceptable".
Ultimately, Palatini says we need to be wary of coffee (and caffeine in particular) because it increases a person's sympathetic activity, changes to the nervous system that can lead to an accelerated heart rate and raising of blood pressure, which is especially dangerous among coronary patients. He says it isn't good for slow caffeine metabolisers (folks who take longer to break down caffeine), causing caffeine to accumulate in their blood where it can lead to negative effects. "Concluding that coffee is safe without distinguishing between different clinical conditions is misleading and may encourage patients to drink as much coffee as they wish," Palatini said.
Rob M. van Dam, an associate professor of epidemiology at the Saw Swee Hock School of Public Health at the National University of Singapore, was a little less harsh toward the new findings. "These studies on coffee and mortality are based on large well-conducted cohort studies," van Dam, who wasn't involved in either study, told Gizmodo. "The results that coffee consumption is associated with a moderately lower risk of mortality during follow-up is not surprising as this has been reported for several previous studies. The new studies add to the available evidence as they show consistent results in various ethnic groups in the US and different countries in Europe."
These generous words aside, van Dam said the only way to truly determine the truth is to conduct randomised trials of coffee and health outcomes. In other words, to run actual experiments.
"Coffee is a plant food that is rich in chlorogenic acid and related phenolic compounds," carbon-based molecules with ring-like structures, "that reduced blood glucose levels in animal studies," he said. "It also contains trigonelline, a precursor of vitamin B3, several minerals such as magnesium, and vitamins such as vitamin B3." He says phenols in coffee confer various health effects, such as reducing the ability of intestines to absorb glucose, preventing the liver from expressing too much glucose, and regulating healthy insulin responses.
But van Dam was also quick to point out that excessive caffeine consumption can lead to unpleasant symptoms, such as nervousness, the jitters, and disrupted sleep. "If you're experiencing any of these [symptoms] it is appropriate to cut down on [coffee] consumption." He added that caffeine consumption during pregnancies might reduce fetal growth and increase a woman's chance of having a miscarriage. "Limiting caffeine consumption in pregnancy to one regular size (~8 fl oz) cup of coffee or less seems thus appropriate."
So where does all this leave us? Clearly, coffee has a lot going for it, and as these new studies attest, it might confer some tremendous health benefits in certain individuals. But a one-size-fits-all approach to coffee drinking is not appropriate. If you're a coffee drinker, be mindful of how coffee affects your health and mental well-being, and adjust accordingly. If you think coffee may exacerbate a pre-existing health condition (such as sleep disorders or cardiovascular health), talk to your doctor. And if you're pregnant, cut back to a cup a day at most.
Otherwise, enjoy that tasty brew.