More than half of all Americans drink at least one cup of coffee every day.
And as well as a rich history, their tasty, energizing coffee habit apparently offers real health-guarding potential to most.
That's despite a California judge's recent ruling that, under Proposition 65, coffee will come with a cancer warning in that state.
That decision is being criticized by the American Cancer Society, given the virtual absence of evidence linking coffee to cancer — see "Carcinogen in coffee?", below.
You'll find many reports about research regarding coffee in the Cocoa, Tea, & Coffee section of our news archive.
Before we get the recent coffee-and-health news, let’s take a quick trip through coffee history.
Coffee: A brief history here and abroad
Coffee is the second-most traded commodity in the world — after oil — and its popularity has grown worldwide, even in tea-centered countries like Japan and China.
From its origins in 15th century Yemen, coffee, conquered the Ottoman Empire in the 16th century and spread to Europe in the 17th century — where it famously fueled many fevered café conversations about politics and culture.
Coffee was intermittently banned by the Ottomans and European rulers alike for making people too “excitable” and prone to revolutionary talk.
Most Americans switched from tea to coffee after the 1773 Boston Tea Party, partly as an expression of freedom from British rule, and partly due to the higher cost of tea.
As founding father and future President John Adams wrote to his wife Abigail about six months after the Tea Party, “…I have drank coffee every afternoon since, and have borne it very well. Tea must be universally renounced. I must be weaned, and the sooner, the better.”
Following the revolution, coffee from the Caribbean remained considerably cheaper than Asian tea — over which the British held a virtual monopoly — and that cost gap helped sustain a habit that’d begun as a beverage-based protest.
Studies from Britain, America, and Europe link coffee to reduced death risk
Every drinker’s hope that coffee is healthful as well as tasty and energizing is supported by three recent evidence reviews.
Let’s examine the findings of these studies, and then address concerns about coffee — which are mostly minor.
One of the new evidence reviews comes from researchers at Britain’s University of Southampton and University of Edinburgh.
They performed a meta-analysis of epidemiological and clinical studies that had looked for links between coffee consumption and health outcomes (Poole R et al. 2017).
(A meta-analysis is a type of evidence review that uses statistical methods to combine the results from multiple studies, to create a clearer, optimally reliable overall picture.)
The UK team reviewed 218 studies, including 201 epidemiological (population) studies and 17 clinical trials.
This mix reflects the fact that there have been relatively few controlled clinical trials testing the effects of coffee, which provide more reliable results.
After comparing the effects of varying rates of coffee consumption — high versus low, some versus none, etc. — the British team’s analysis showed that it’s generally safe to drink three to four cups a day and this habit confers some significant health benefits.
Their statistical analysis linked drinking three to four cups a day to reduced risks for three things:
Additionally, having a “high” versus “low” consumption of coffee was linked to a lower risk of cancer, as well as reduced risks for neurological, metabolic, and liver conditions.
As they wrote, “Coffee consumption seems generally safe within usual levels of intake, with … [the] … largest risk reduction for various health outcomes at three to four cups a day … [which is] … more likely to benefit health than harm [it].”
An evidence review by scientists from Saint Luke's Mid America Heart Institute arrived at very similar conclusions (O'Keefe JH et al. 2018).
The authors reported these on-average effects of drinking three to four cups daily, which, they said, delivers "the most robust beneficial effects”:
Finally, a huge epidemiological study published last year — which involved more than one-half million people in 10 European countries — came to similarly positive conclusions:
“Coffee drinking was associated with reduced risk for death from various causes. This relationship did not vary by country.” (Gunter MJ et al. 2017)
Benefits aside, the authors of the three evidence reviews conveyed a few caveats about the risks of coffee in some groups of women.
Cautions to women who are pregnant or at high fracture risk
There are two groups of women for whom coffee may do more harm than good — those who are pregnant or at risk for bone fractures.
The researchers’ analysis linked high versus low or no coffee-consumption to several complications:
Women at risk of fracture
The analysis showed that fracture rates were higher among women — not men — with osteopenia or osteoporosis.
It’s not yet clear why coffee would negatively impact pregnant women and women at high risk of fractures.
Other coffee concerns: mostly minor
Detractors point to coffee’s acidic nature, give some people the jitters or insomnia — and its alleged power to raise cortisol (stress hormone) levels.
Natural health advocates often tout the benefits of tea and claim that drinking regular coffee “exhausts” the adrenal glands … although tea contains about half or more as much of the supposed guilty party, caffeine.
While some clinical studies find that coffee stimulates secretion of cortisol — or tends to keep circulating levels from dropping — others find no such effect.
Caffeine does stimulate the release of adrenal “fight-or flight” hormones such as norepinephrine and epinephrine.
So, it’s conceivable that sipping coffee all day could raise your average norepinephrine and epinephrine levels.
But there’s little good evidence that moderate coffee consumption raises stress levels in most people ... see Coffee and Tea May Reduce Stress.
Coffee with caffeine can also raise blood pressure in people unused to drinking it, but this effect usually disappears after drinking it for a few days.
Although large amounts of caffeine can be risky for people with heart-rhythm problems, moderate caffeine consumption (200-400mg daily) appears safe.
Coffee for all-nighters: Maybe not a good idea
Coffee is clinically proven to boost mental focus and clarity.
That's why coffee is the crutch that many — especially students and night-shift workers — rely on to stay awake and alert.
However, this seems to be a bad idea. One study found that students who drank moderate to high amounts of coffee scored significantly higher on tests measuring anxiety and depression, and lower academic performance, compared with coffee abstainers.
Although coffee-chugging students showed some signs of depression on psychological tests, caffeine is generally mood-elevating, so that finding may simply confirm that moderation is key when it comes to caffeine.
Unsurprisingly, the high-consumption students also reported significantly more restlessness, nervousness, irritability, and insomnia.
Don’t eat enough antioxidant-rich produce? Coffee’s got you covered
Coffee offers very high level of antioxidants — primarily polyphenols, plus the considerable antioxidant powers of caffeine.
In fact, coffee is the top source of antioxidants in the average American’s diet — partly because many Americans don’t eat much produce, making coffee the easy winner by default.
Most research suggests that coffee’s high antioxidant levels and particularly potent antioxidant profile account for its health benefits.
And coffee features some unusually powerful, broadly beneficial antioxidants — such as chlorogenic acid — that aren’t as abundant in other foods and drinks.
Carcinogen in coffee?
Most evidence links coffee to reduced risks for most cancers, including post-menopausal breast cancer.
This is a typical finding, despite the facts that most breast cancers are estrogen-dependent and that drinking four to five cups of coffee per day during the early part of her menstrual cycle temporarily raises a woman’s estrogen levels by up 70 percent.
So why did a Superior Court judge for Los Angeles County recently rule that coffee must display a cancer warning under California’s Proposition 65?
It was because coffee contains acrylamide, which is a potential carcinogen and neurotoxin.
Acrylamide is widely used in industrial processes and cosmetics and is formed when proteins and carbohydrates — especially carbohydrates — reach high temperatures, such as in fried, browned, and baked foods.
Levels of acrylamide in coffee are not particularly high, but they’re just high enough to violate the extremely strict — some scientists say overly strict — limits set by Proposition 65.
Be aware that acrylamide levels are substantially lower in dark roast coffee than in light roast coffee. So, if you want to minimize your intake from coffee, choose darker roasts.
Acrylamide appears to promote cancer in rodents, but links to human cancers are (with some exceptions) generally weak.
For example, a Japanese epidemiological study published last month found no link between dietary intake of acrylamide and the risk for breast cancer among 48,910 women aged 45-74 (Kotemori A et al. 2018).
Neurotoxic effects have been seen primarily among industrial workers exposed to amounts much larger than those in foods.
Raise a toast to coffee
The largely positive evidence on coffee gives drinkers a great excuse to continue their habit.
But remember that there is a sweet spot — three to four typical six-ounce cups of coffee a day — which translates to 18 to 24 ounces.
Using Starbucks as the standard, that’s two to three tall coffees (12 ounces each) or two grandes (16 ounces each).
You may want to skip the ventis, because at 24 ounces, you’ll hit your quota with just one cup!
FYI, the caffeine content of coffee ranges from about 65mg for a standard one-oz. shot (30 ml) of espresso to about 145mg for an 8 oz. cup (237 ml) of drip coffee.
Despite popular belief, espresso contains no more caffeine per ounce — and typically less — than drip coffee.