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Metafact Review: Coffee
Many of us don’t just like our morning cup of coffee – without it, we seem to function poorly. The alertness and stimulation of caffeine is well known – making it a daily ritual for most of the world making coffee is the world’s most popular beverage (excluding water).
In Australia for example, 75% of people drink coffee daily, while some 60% of Americans do. But its European nations that are the power coffee drinkers. Finland has the world's highest coffee consumption, with many drinking up to 10 cups of coffee per day! The obsession with coffee across the world has made it the second most traded commodity worldwide after oil.
For any drink so popular as coffee – people have claimed all sorts of things. Some say coffee fights Alzheimer's, helps weight loss, and makes us live longer! Are these true? What is the evidence behind them? Is there a science to making a good cup of coffee? And what level of coffee consumption is safe?
This is one of our most popular reviews where we asked independent experts from across the globe to review the facts. Here's what we found...
2,000,000,000: Approximate number of cups of coffee consumed every day across the world
$127,000,000,000: The value of the global coffee market in 2022
51: Number of countries that produce coffee beans
40%: Brazil's proportion of global coffee production – making it by far the largest supplier of coffee
45%: European proportion of global coffee imports – making it the largest importer of coffee
32,938: Number of Starbucks coffee houses around the world
1884: The year when espresso was invented by Italian Angelo Moriondo for a “new steam machinery for the economic and instantaneous confection of coffee beverage.”
1890: The year when instant coffee was invented by David Strang in New Zealand
From Ethiopia to Starbucks
The word coffee derives from the word Kaffa - "a drink from berries" - also the name of a region in the South Western Ethiopian highlands where coffee was thought to be first discovered. As the popular story goes, in the 9th century an Ethiopian goat herder named Kaldi gave his goats a light red fruit from a shiny dark-leaved shrub (the coffee arabica shrub). To his surprise the normally dull goats became exceptionally lively, energetically skipping around. Suspecting hidden powers in this unknown fruit, Kaldi tried them himself – and sure enough, he felt energised and alert.
Coffee beans started to be roasted and infused into drinks during the 16th century. Coffee spread rapidly throughout Turkey and the Ottoman empire as a replacement for alcohol, which was banned throughout the Muslim world. The first documented coffee house (called kaveh-kanes) opened in Istanbul, Turkey **in 1554.
Europe discovered coffee for the first time via Italian merchants in the 17th century. It was met with strong resistance by the Catholic Church who called it 'the devil's drink'. Venice's first coffee house ("bottega del caffe`") opened in 1645 and coffee spread quickly throughout Europe with England's first coffee house opening in 1650. It wasn't until 1676 that Boston opened the first coffee house in the United States. That is a long way from today's biggest coffee company, Starbucks, with 32,938 coffee-houses across the world making everything from black coffee to caramel whipped cream lattes.
Is there science behind good coffee?
Coffee beans are the first component of good coffee. Coffea arabica makes up 75% of the world's coffee trade (Coffea robusta makes up the rest). Once the beans are sourced, the roasting takes place, where heat transforms the green bean into roasted brown beans that can be ground.
Once ground, there are 3 broad methods to make drinkable coffee: espresso, filtered and instant. The active caffeine component of coffee is ~2-3%, the rest made up mostly of tannins, proteins and oils. A variety of other bioactive chemicals, aromas and scents are also present in coffee. Both the caffeine content and flavor vary widely depending on a number of factors.
Dr Christopher Hendon, a chemist from the University of Oregon writes in detail about the chemistry and physics of making coffee.
What to do at home for a better coffee?
For filtered coffee three factors are most important according to Dr Hendon: water chemistry, particle size distribution produced by the grinder and coffee freshness.
Water quality: "Given coffee is an acidic beverage, the acidity of your brew water can have a big effect. Brew water containing low levels of both calcium ions and bicarbonate (HCO₃⁻) – that is, soft water – will result in a highly acidic cup, sometimes described as sour. Brew water containing high levels of HCO₃⁻ – typically, hard water – will produce a chalky cup, as the bicarbonate has neutralized most of the flavorsome acids in the coffee.
Ideally we want to brew coffee with watercontaining chemistry somewhere in the middle. But there’s a good chance you don’t know the bicarbonate concentration in your own tap water, and a small change makes a big difference. To taste the impact, try brewing coffee with Evian – a bottled water with one of the highest bicarbonate concentration, at 360 mg/L" says Dr Hendon.
Particle size: The particle size distribution your grinder produces is critical, too. Dr Hendon explains there are two different schools of thought on particle size. "One school of thought supports grinding the coffee as fine as possible to maximize the surface area, which lets you extract the most delicious flavors in higher concentrations. The rival school advocates grinding as coarse as possible to minimize the production of fine particles that impart negative flavors. Perhaps the most useful advice here is to determine what you like best based on your taste preference" he says.
Bean freshness: "Roasted coffee contains a significant amount of CO₂ and other volatiles trapped within the solid coffee matrix: Over time these gaseous organic molecules will escape the bean. Fewer volatiles means a less flavorful cup of coffee. Most cafes will not serve coffee more than four weeks out from the roast date, emphasizing the importance of using freshly roasted beans" he says.
One can mitigate the rate of staling by cooling the coffee (as described by the Arrhenius equation), while storing coffee in an airtight container in the freezer will significantly prolong freshness, says Dr Hendon.
What about espresso?
Espresso is the most complicated brewing method because it requires precise measurements and is also the basis for lattes and cappuccinos. To make espresso, hot water is forced through a finely-ground bed of coffee.
The barista decides the types of beans and how finely ground the particles are. The machine’s water pressure, temperature and brew volume are also crucial when it comes to taste. Thousands of chemicals and aromas are produced via a delicate balancing act for the barista.
Dr Jamie Foster from the University of Plymouth teamed up with Dr Hendon to derive the factors most important for a good espresso. They found that the quality of the coffee plant/green bean to be by far the most important factor for good espresso.
"Provided all other brewing parameters are sensible, I would say that quality beans is the most influential factor on taste" wrote Dr Foster. After beans, water quality is the next most important. "Yes. Extremely. Aside from bean quality, I would say that it is probably the most important thing. Luckily, obtaining quality water can be achieved quite easily by filtration. I refer interested readers to the book Water for Coffee: Science Story Manual" says Dr Foster. The quality of roast is also important says Dr Foster. Interestingly, the quality of espresso machine is the least important of the four factors.
Is coffee ok during pregnancy or breastfeeding?
Caffeine is a known stimulant, so it's often claimed that drinking coffee during pregnancy or breastfeeding might be harmful to babies. "Overall, low levels of coffee consumption are not convincingly or consistently associated with any adverse pregnancy outcomes or outcomes during childhood" writes women's health epidemiologist Dr Kesha Baptiste-Roberts from Morgan State University. "As such one should adhere to the American College of Obstetrics and Gynecology recommendation of <200 mg of caffeine per day" - which is ~1-2 cups a day.
"Caffeine passes into breast milk, and caffeine has a longer half-life in infancy with even more delayed elimination in breastfed infants" writes Dr Baptise-Roberts. "However, the clinical use of caffeine in neonates appears to be relatively safe. There are still too few studies with limited quality to make conclusive statements" she writes.
"A recent massive review of caffeine intake in pregnancy confirms previous advice that intakes of less than 300mg caffeine per day in pregnant women is safe" says Dr Ian Musgrave, a pharmacologist from University of Adelaide. "But cut back on the double espressos and don't binge on chocolate [dark chocolate contains caffeine]" he says.
Do coffee drinkers live longer?
A number of studies (like this and this) have suggested that people who drank coffee had a lower risk of dying of any cause – and specifically, of dying from heart disease and cancer. More evidence has been published recently say the experts.
"A huge review published in BMJ in 2018 showed that coffee consumption was more often associated with benefit than harm for a range of health outcomes" writes coffee health expert Dr Joanna Mikolajczyk-Stecyna from Poznan University. "However, we have to remember that some of us are (so called) "fast" and the other "slow" caffeine metabolizers. Therefore drinking coffee, which apart from hundreds of biologically active compounds, includes also caffeine, affect us in different way. Habitual coffee consumption seems to be beneficial for adult, but not for children and adolescents. Because drinking coffee is associated associated with lower risks for cardiovascular diseases, main reason for death, it can be linked to longevity" she writes.
"Drinking moderate amounts of coffee – about three or four cups a day – is more likely to benefit our health than harm it, our research shows" wrote Dr Robin Poole from University of Southampton. Those benefits include lower risk of heart disease, type-2 diabetes, liver disease, some cancers, Parkinson's and Alzheimer's.
Despite the correlative evidence, "we still can’t say coffee was the cause of the lower risk of death" writes pharmacologist Dr Ian Musgrave from the University of Adelaide. "There may be some other environmental variable that was not accounted for. Coffee consumption may entail more walking, for instance, which was not captured in the lifestyle questionnaires. But it is still plausible coffee causes the lowered death risk. While coffee is most notable for its caffeine content, it also contains a host of antioxidants such a caffeic acid and cholorogenic acid, which might have health benefits."
Does coffee help with weight loss?
In 2019 researchers from the University of Nottingham in the UK published a study suggesting caffeine increases brown fat. Brown fat activity burns energy, which may help with weight loss - so it got headlines. Dr Andrew Carey, an obesity expert from the Baker Heart and Diabetes Institute writes in detail about this study. Although caffeine did stimulate brown fat, it was in lab cells and "for a human to reap the benefits seen in the cells, we estimate they’d need to drink at least 100 cups of coffee.. current evidence suggests we shouldn’t start thinking about it as a weight loss tool, nor that it has anything meaningful to do with brown fat in humans" writes Dr Carey.
Another more recent study reported that consuming caffeine half an hour before aerobic exercise can actually help people burn fat. Dr Neil Clarke writes in detail about this study. He suggests that burning more fat after ingesting caffeine might be because "Caffeine promotes lipolysis (the process by which fats are broken down), due to a greater release of adrenaline. Lipolysis then causes fatty acids to be produced as a result. These fatty acids are then released into the blood and transported to muscle to be used as energy" he writes.
Caffeine also allows greater energy expenditure via deactivating the compound adenosine and stimulating the central nervous system allowing more muscle fibres to be used during excercise. "But it’s important to note that the effects in this most recent study may have been increased due to this exercise being performed in a fasted state. When exercising without eating before, fat oxidation is naturally higher" says Dr Clarke.
Other experts say "Coffee likely has a minimal effect on weight loss by itself" writes nutritionist Dr Neil Schwarz from the University of South Alabama. "The caffeine in coffee may increase metabolism, but it is unlikely to be enough to stimulate meaningful weight loss. Additionally, once any creamer or sugar is added to coffee, the additional calories offset any increase in metabolism. Black coffee may help slightly increase metabolism and decrease appetite. These are both helpful for inducing a caloric deficit for weight loss, but, overall, it is the balance in energy output versus input that will determine weight loss."
Is 400mg of caffeine the safe threshold?
How much coffee is safe? Neuroscientist and coffee expert Dr Astrid Nehlig from INSERM in Paris writes a good overview for us:
"The European Food Safety Authority and others around the world have published recommendations about the maximal safe daily doses of caffeine as well as the maximal doses recommended in one sitting. These figures have been estimated based on the brain and cardiovascular effects of caffeine. As confirmed by the experts, 400 mg a day is a safe limit for caffeine intake - but there are some differences based on the demographic and age:
Type of population| Maximal dosage advised in one sitting (mg)| Maximal daily dosage advised (mg or mg/kg)
Adults |200 mg (2 cups coffee) |400 mg (4 cups)
Intense sports activity in adults |200 mg up to 2 h before the exercise |Not determined
Pregnant women |200 mg (2 cups) |200 mg (2 cups)
Nursing women |200 mg (2 cups) |200 mg (2 cups)
Adolescents and children |Not determined |3 mg/kg
Does coffee help with exercise and sports?
Caffeine is one of the most researched substances reported to help athletes perform better and train longer and harder writes Dr Neil Clarke, sports scientist from Coventry University. As a result, professional and amateur sportspeople often take it as a performance-enhancing “ergogenic” aids for a wide range of activities. These include intermittent exercise such as football and racket sports, endurance exercise such as running and cycling, and resistance exercise such as weightlifting.
"Research has shown that pure caffeine can help endurance athletes run faster and cycle for longer" writes Dr Clarke. "It can help footballers to sprint more often and over greater distances, and basketball players to jump higher”. But will drinking coffee have the same effect as caffeine tablets? Yes says Dr Clarke “providing that the amount of caffeine is matched”.
What about the potential effects on the heart? "Caffeine improves exercise performance," writes cardiologist Dr Vitor Valenti. "However, if you have a cardiovascular disorder, we suggest you not intake caffeine before effort, in order to avoid any health complication during recovery."
Does coffee cause dehydration? No. It is often suggested that coffee causes dehydration and its consumption should be avoided or significantly reduced to maintain fluid balance. However, a number of studies suggest that coffee, when consumed in moderation i.e. around four cups per day provides similar hydrating qualities to water and that drinking coffee as part of a normal lifestyle doesn't cause fluid loss in excess of the volume ingested.
Does coffee lower the risk of Alzheimer's Disease? There is no clear evidence of this. There are some suggestions that coffee drinkers have lower rates of diseases like Alzheimer’s disease. However, the key question is why. Correlation does not equal causation.
Does coffee reduce the risk of cancer? Unlikely.
Does the acrylamide in coffee cause cancer? Unlikely, too. Acrylamide isn't good for you but the amount present in coffee makes no observable contribution to cancer risk. There is no strong evidence for a link between drinking coffee and developing cancer. While there have been occasional studies suggesting an increased risk in bladder cancer, overall the vast majority of rigorous studies suggest that if coffee drinking has any effect at all it actually offers a mild protective effect from some cancer types.
Does caffeine impact sleep quality? Yes, studies have shown that caffeine intake, as low as 100 mg can:
delay the timing of the body circadian clock
reduce sleep efficiency and sleep duration
perhaps even more dramatic, decrease the electrical "depth" of sleep (as measured by the spectral power of the delta brain waves during non-REM sleep).
Is coffee drinking genetic?
My answer is yes. Twin studies have shown that coffee drinking is approximately 35-60% genetics depending on the differences in coffee cultures between populations. For Australians, 51% of coffee drinking is genetics and the remaining 49% is due to exposure to environmental factors such learning to know the pros and cons of coffee or peer influences.
Genes that have a major influence on coffee drinking are those involved in the caffeine metabolism. People with the genetic variants that make them metabolize caffeine quicker often drink more coffee. Genes involved in taste perception also affect coffee preference and hence coffee consumption. For example, people with the bitter supertaster gene often find coffee more bitter and drink less coffee.
I need to note that while humans are born to dislike bitter taste, as a natural defensive system to avoid eating poisonous food, our preference could change over time due to exposure to environmental factors. Therefore, some people might enjoy drink coffee because of its bitterness!
Dr Daniel Hwang from University of Queensland
To make good espresso coffee, experts say the quality of beans/freshness are the most important factor followed by water quality and roasting. The equipment is the least important.
Coffee drinkers live longer according to studies, but it's uncertain whether coffee is causing people to live longer without controlling for their lifestyle.
Coffee doesn't cause dehydration. It improves exercise performance/duration and therefore may help some in promoting weight loss.
The impact of coffee heavily depends on whether you are a slow or fast metabolizer. Alter your habits to ensure you don't have coffee in the afternoon if you fall into the slow metabolizer category which would impact your sleep.
3-4 cups of coffee is healthy or 400mg of caffeine. For pregnant women, 1-2 cups is the safe level of what experts recommend.
Enjoy your coffee!