In March this year, after a project that lasted just shy of two decades, scientists at Japan's National Cancer Centre released some intriguing results.
Their study, published in The American Journal of Clinical Nutrition, tracked the lives – and sometimes deaths – of more than 90,000 people. Its conclusion was remarkable: "The habitual intake of coffee is associated with lower risk of total mortality and three leading causes of death in Japan."
Actually, it wasn't that remarkable. The study recorded unusually unambiguous findings, but it was broadly in line with a growing body of research that suggests drinking two to five cups of coffee a day may significantly reduce your risk of dying from a wide range of nasties, including melanoma, diabetes, and Alzheimer's.
With a few variants, the results hold true for posh coffee, instant coffee, and decaf. They represent a complete reversal of the received wisdom of the 1980s, when coffee-drinking was suspected to cause cancer, heart disease and birth defects. Still, for many people today, the suspicion that coffee is bad for you lingers. It seems somehow counter-intuitive that consuming the world's most common addictive substance may actually be a good idea.
"I believe that coffee can be a dietary bad guy only if it is consumed in high dose, when caffeine is present," Italian coffee scientist Dr Luciano Navarini said. "But as far as I know, healthy adult coffee drinkers normally keep to a fixed number of cups all life long, and they exceed only in very special situations, when it is necessary to stay alert for some reason. Scientific literature indicates that moderate coffee consumption seems to be a good habit rather than a dangerous vice."
Navarini works for Italian coffee giant Illycaffe, so perhaps he may be expected to say that. Increasingly, however, independent as well as industry-aligned scientists are crowding into coffee research.
Many are keen to seek chemical explanations for epidemiological results. Research – like the Japanese study – over the past couple of years has shown apparent links between drinking several cups daily and a reduced risk of, among other things, multiple sclerosis, liver cancer, dementia, skin cancer, breast cancer, heart disease, cerebrovascular disease, respiratory disease, colourectal cancer, and type 2 diabetes.
Correlation, however, is not evidence of causation, so the race for answers is well and truly on. The task is immense. Coffee is a supremely complex beast, containing more than 1000 chemical compounds. As well as caffeine, these include a wide range of antioxidants, proteins, fats, minerals, and a class of aromatic geegaws called pyridines.
Research over the past couple of years has revealed that many of these compounds have known, or suspected, health effects.
Spanish research released last week found that caffeine interacts with adenosine receptors in the brain, thereby boosting the levels of mood-lifting dopamine. This may produce methods of treating depression. Caffeine has also been implicated in reducing the risk of liver and throat cancer, as well as protecting against Parkinson's disease and type 2 diabetes.
A related substance, caffeic acid, has been shown to restrict the growth of the hepatitis C virus.
Another prime research target is a polyphenol called chlorogenic acid or CGA. A 2013 study found that CGA improved attention span and alertness, and reduced headache, even among decaffeinated coffee drinkers. CGA has also been implicated in boosting certain types of gut bacteria linked to managing diabetes and cardiovascular disease.
The evidence for the health benefits of CGA, however, remains mixed. In 2014, University of WA pharmacologist Dr Natalie Ward co-authored a study into CGA consumption in mice. The study found the compound had no effect on obesity, glucose intolerance or insulin resistance.
"It was a hugely significant result, and very surprising", she said. "All the epidemiological evidence suggests that coffee brings a very big protective effect in these areas, but that wasn't the conclusion we came to at all."
Ward thinks an explanation for the unexpected result may stem from the use of CGA in isolation, or because it was extracted from green, unroasted, coffee beans. She added that it was concerning that green bean extract was being promoted as a weight loss product, when, in mice at least, it doesn't seem to work.
"I think there can be problems with taking a single extract," she said. "You see it other areas: single vitamins don't do anything, but fruit and vegetables are good for you."
Ward is continuing to research various aspects of coffee, trying to find what, if anything, underpins the population study results. Despite her failure to make fat mice thin, she remains optimistic.
"I think there's something there," she said. "I don't think it will turn out to be a miracle drink, but I think there is definitely something there to be found. For a long time coffee had a stigma attached to it, but where is the evidence to suggest coffee is bad for you? I don't think there is any."
Recent television spruiking of the slimming power of green beans might be wide of the mark. However, the slew of recent studies recording an apparent link between coffee-swilling and reduced risk for a range of conditions – including liver, breast, skin and colourectal cancers – suggests that something a lot more powerful than health faddism is going on.
If empirical, peer-reviewed evidence of mechanistic links between the brown stuff and better health emerges, it's a fair bet that global demand for the product will increase dramatically. And that will be challenging, in terms of the world's ability to grow the crop.
According to the International Coffee Organisation, in 2014 global consumption of coffee topped 8940 million kilograms. (For those wearing anoraks: at seven grams per serve, that's about 1,269,480,000,000 cups.) Global production, however, was short by 420 million kilograms last year with the shortfall made up from reserves. Coffee production last year dipped 3 per cent on 2013 figures.
Australia, of course, prides itself on being a nation of coffee drinkers. The statistics, however, show a rather more nuanced picture. In terms of coffees consumed per head, for instance, we fail to make the top 10 listing. According to Statistica.com, Finland wins first prize, followed by Sweden, the Netherlands, Germany, Norway, Denmark, Belgium, Brazil, Tunisia, Slovenia, USA, South Korea and Japan.
Roy Morgan Research figures show average Australian weekly coffee drinking has declined over the past five years from 10.5 to 9.2 cups. The dip, however, may merely indicate a trend towards stronger brews – especially since home coffee-machine ownership increased from 28 per cent to 36 per cent during the same period.
But however you choose to finesse the stats, coffee remains a big business in Australia. Industry analysts Ibis World calculate that the domestic coffee trade currently employs more than 86,000 people and pulls in annual revenue of about $4 billion.
All of which is good news indeed for coffee roasters and sellers. Unlike other frequently consumed beverages, such as cordials, sodas, energy drinks and alcohol, it is unlikely that coffee will be subject to health and safety warnings any time soon. Indeed, it may eventually end up sitting happy and self-satisfied next to apples and broccoli on the food pyramid.
But not yet – not yet. Professor Elvira Gonzalez de Mejia of Illinois University is one of the world's leading experts on coffee and health. In a 2014 overview of the subject written for the journal CellPress, she stated that available data supported "the view that habitual coffee consumption has several health benefits, including lower risks of Parkinson's and Alzheimer's disease, a favourable effect on liver function, a possible role in weight loss, and a decreased risk of developing certain cancers."
She added that the evidence for coffee in managing type 2 diabetes and cardiovascular disease was "largely reassuring" and that consumption of two to four cups a day "is not associated with adverse effects".
de Mejia stressed the need for more research before concluding that epidemiological evidence pointed to predictable clinical uses.
"More consistent human studies are needed," she said. "Standardised coffee samples must be prepared and tested in human studies. The reproducibility of such studies will certainly help to answer these questions."
She also sounded a note of caution regarding possible outcomes of the barrage of ongoing research into the therapeutic potential of coffee's myriad components. Isolating individual compounds and fashioning them into health products – as is currently happening in the medical marijuana industry, for instance – could lead to problems.
"It is better to recommend 'whole foods' rather than isolated compounds," she said. "There is always the risk of using mega-doses of individual compounds; this may bring some risk."
Dr Simon Drew, of the Florey Department of Neuroscience and Mental Health at University of Melbourne, takes a different view. Recently he worked with Navarini and others on a study into how roasting coffee beans changed their antioxidant structures.
"Willow bark was used as an analgesic for millennia before scientists finally extracted salicin from it, a discovery that led to aspirin," he said. "Likewise, something beneficial may be hiding within your daily brew."
Drew's research is not aimed directly at investigating health claims made for coffee. Instead, he and Navarini set out to map exactly how antioxidant types and levels were affected by various roasting, storage and brewing techniques. The results may assist other scientists trying to understand how coffee-derived antioxidants behave in the body.
Like de Mejia, Drew is cautiously optimistic about coffee's health potential, but is reserving judgement until more evidence comes to light. "In terms of antioxidant intake alone, the jury is probably still out," he said. "But there's much we don't know about other potential benefits. Coffee is a melting pot of chemical compounds and the roasting process leads to many new ones."
He suggested that a challenge common to all coffee-related research concerned dosage levels.
"The question is whether the beneficial components of coffee can be obtained from low to moderate consumption in order to avoid other unwanted side effects," he said.
"As a related example, moderate alcohol intake has been linked with decreased risk of cognitive decline and dementia. But drink too much and your risk goes up. The trick is to find that 'therapeutic window' in which you can indulge your senses."
ScienceDirect, the database maintained by academic publishing house Elsevier, has listed so far this year more than 2500 new papers and book chapters concerning coffee and health. That represents just a fraction of the research going into the subject.
"I have measured out my life with coffee spoons," wrote TS Eliot in 1920. If the evidence continues to roll in, we all may soon be following suit – on doctors' orders.
A brief history of coffee
When coffee reached Europe at the start of the 17th century, medical claims for and against its use were immediately raised – although not always from the noblest of motives.
In the 1570s a German physician called Leonhard Rauwolf travelled through the Middle East and collected samples of coffee beans, commonly consumed in Turkey, Syria and Egypt. Back in Europe, several doctors joined forces with religious groups to oppose the stuff on the unedifying grounds that it was a Muslim vice.
Thankfully, the pontiff of the day – Pope Clementine VIII – wasn't as bigoted as his advisers . In 1605, after tasting the strange new drink, he pronounced it delightful and perfectly safe for Christians.
By mid-century, coffee houses were opening at a rapid rate across Europe and Britain. A pamphlet produced in London in 1652 to promote the city's first coffee shop declared the beverage to be a cure for coughs, dropsy, gout, scurvy and miscarriage.
Within a couple of decades, London boasted hundreds of such cafes. Many doctors at the time condemned the drink as poisonous. The same thing happened in France, where doctors in Marseilles alleged that it caused palsy, blood diseases and impotence. (A pamphlet written by a women's group in London concurred with that last bit, denouncing it as "enfeebling", rendering their husbands "unfruitful".)
In 1675, the British King Charles II used the arguments about health merits as an excuse to order all of the country's coffee shops closed down. His real reason had little to do with concern for his subjects' welfare. He was convinced that coffee shops were meeting places for radicals determined to dethrone him.
The King's move, however, was unsuccessful – with the coffee shop proprietors and their customers simply ignoring his edict en masse. After that, he quietly withdrew his objections, having learnt a most valuable lesson – never, ever, try to cut off a punter's caffeine supply.
A stain on science: the 'coffee ring phenomenon'
Coffee being the most ubiquitous beverage in the world, it is hardly surprising that few if any of its many properties have not been studied intensively.
One area of research in which Australia is leading the field concerns the deceptively complex matter of why spilt coffee stains the way it does.
You have probably noticed, in a not overly curious kind of way, that coffee dripped onto something – the magazine you're trying to read, say, or your laptop's track-pad – tends to form a circle, which dries with a distinct dark ring at the circumference.
This is known as the "coffee ring phenomenon" and was first described in the journal Nature in 1997. Since then, it has been subject to a surprisingly large array of further studies – as scientists investigated the precise physics and chemistry that cause the rings to form.
The answers are surprisingly complicated. Broadly, however, water at the edges of a drop of spilt coffee evaporates quickly, resulting in a higher concentration coffee particles at the circumference than in the middle of the mess. Et voila! A ring.
The latest work on the coffee ring phenomenon was published this year, by Azadeh Nilghaz, Liyuan Zhang, and Wei Shen from the Department of Chemical Engineering at Monash University.
The researchers looked for the reasons why, sometimes, spilt coffee fails to produce either a ring or a circular stain. They concluded that the coffee ring phenomenon could be altered, and even prevented, by the absorbent properties of the surface on which the coffee is spilt.
The findings may seem trivial, but their implications are actually quite significant. Calculating the coffee ring phenomenon is a critical part of designing many precision machines, from paper-based diagnostic sensors for blood analysis to ink-jet printers.