The prospect of peak coffee raises the menace of massive caffeine withdrawal, with hordes of headachy addicts rendered into grouchy slackers. Could a cut in coffee production also cost us the many health benefits that coffee seems to provide?

For ages, the bitter black brew has been scorned as jet fuel for jittery insomniacs, providing nothing more than a momentary surge of focus and energy.

But recently, some researchers are starting to see java as the juice of the gods: In some studies, coffee appears to be protective against dementia, type 2 diabetes and even several types of cancer.

Coffee, it turns out, is loaded with polyphenols, anti-oxidant chemicals that fight damaging free radicals, which are implicated in many of the diseases of aging.

Caveat quaffer

Before we fill our cup with a discussion of the health benefits of coffee, remember these cautions:

For all these reasons, we are not prescribing coffee as medicine. But then, do we drink coffee for medicine, or for the taste, the excuse to talk things over with a friend, the acceleration physical and mental energy?

So bottoms up, and let’s check some recent studies showing how coffee affects dementia, diabetes, cardiovascular disease and cancer

Coffee: Good for your brain?

Many studies over the past decade have suggested that coffee can partly block Parkinson’s disease, a movement disorder that afflicts millions of elders. In 2006, ² researchers reported on a 22-year study of Finns – who boast Earth’s highest average coffee consumption – and found that people who drank more than 10 cups a day had about one-quarter the risk of Parkinson’s as non-drinkers. (Do Finns ever finish guzzling? While only 5 percent of the sample abstained, about 10 percent drank at least 10 cups a day!)

The researchers suggested that since Parkinson’s may be caused by oxidative attack on neurons, coffee’s protection may arise from its anti-oxidants.

Several studies – the results are inconsistent but suggestive – have linked caffeine and coffee with a reduction in Alzheimer’s disease. In 2010, after a 21-year study, researchers from Finland and Sweden³ reported that “coffee drinking of three to five cups per day at midlife was associated with a decreased risk of dementia/Alzheimer’s disease by about 65 percent at late-life.”

Research using mice with a genetic tendency to Alzheimer’s shows that coffee and caffeine improve learning and memory while reducing the beta amyloid plaques that mark Alzheimer’s. In 2011, when Gary Arendash and Chuanhai Cao of the University of South Florida compared coffee, caffeine and decaf,⁴ coffee was most effective at stimulating chemicals that apparently defend against Alzheimer’s. The researchers wrote that “coffee may be the best source of caffeine to protect against [Alzheimer's disease]” because another coffee chemical acts with caffeine to enhance protection.

Arendash did not respond to our email but said in 2009 that he’s seen “evidence that caffeine could be a viable ‘treatment’ for established Alzheimer’s disease, and not simply a protective strategy. That’s important because caffeine is a safe drug for most people, it easily enters the brain, and it appears to directly affect the disease process.”

Coffee ‘n cancer

Can coffee help protect against cancer? Sometimes.

Photo Florida Alzheimer’s Disease Research Center

Caffeine removed harmful beta amyloid plaques from the brains of mice that simulate Alzheimer’s disease.

A study of coffee and liver cancer followed 60,323 Finns for a median of 19.3 years. After adjusting for factors like age, alcohol and smoking, the hazard ratio of those who drank four to five cups was 0.44.

Hazard ratio means the probability of an outcome, compared to the reference group (non-drinkers, in this case). All other things being equal, abstainers were three times as likely to get liver cancer as those who swilled eight cups a day.⁵

To decipher conflicting or inconclusive studies, scientists can pool data using meta-analysis, a technique that sets standards for acceptable studies and then statistically groups the results.

In 2010, Mia Hashibe, in the department of family and preventive medicine at the University of Utah re-analyzed⁶ nine studies and found a 39 percent reduction in mouth and throat cancers among people who drank at least four cups. “Since coffee is so widely used and there is a relatively high incidence and low survival rate of these forms of cancers, our results have important public health implications that need to be further addressed,” said Hashibe. With such a large sample, “We had more statistical power to detect associations between cancer and coffee.”

If we shift the focus to all cancers, a new meta-analysis⁷ of 59 studies showed that each additional cup of coffee reduced the incidence of cancer by 3 percent.

The results concerning breast cancer are less encouraging. A 2008 report⁸, based on data from 85,987 women, found no significant link to coffee, decaf or tea, except for a slight reduction in breast cancer among post-menopausal women who ingested a significant amount of caffeine.

Similarly, a 2009 study in the Netherlands ⁹ found no association between coffee and breast cancer.

Ironically, coffee contains a chemical that could stimulate the many breast cancers that respond to estrogen by growing, according to Clinton Allred, an assistant professor of nutrition at Texas A&M University. Allred, who has found large amounts of a plant estrogen called trigonelline in coffee, says, “This is one of the least studied compounds I have ever been around.”

In the lab, Allred showed that trigonelline can affect cells even when it is thousands of times more dilute than the effective concentration of isoflavone, a common plant estrogen found in soy.

Allred is not worried about trigonelline, since people have been guzzling coffee for a long time, and plant chemicals consumed in a whole food or beverage act differently than they do in isolation in the lab. “People with a healthy diet that is high in plant products are exposed to these kinds of compounds all the time.”

A diabetes connection?

Could coffee slow the epidemic of type 2 diabetes, which disrupts sugar metabolism, which raises blood sugar that harms small blood vessels in the kidney, eye and heart? A 2006 study¹⁰ of 88,259 American women showed that drinking at least four cups of coffee reduced the diabetes rate to 53 percent of the rate among non-drinkers. Although both coffee and decaf (but not tea), were beneficial, diabetes prevention was most closely linked to coffee intake rather than caffeine intake.

According to a meta-analysis¹¹ based on more than 450,000 people from Asia, North American and Europe, “Every additional cup of coffee consumed in a day was associated with a 7 percent reduction in the excess risk of diabetes type 2. … Drinking three to four cups of coffee per day was associated with an approximate 25 percent lower risk of diabetes… .”

If coffee reduces diabetes, could it deter cancers associated with diabetes? A 2007 exploration¹² of the soaring rate of cancer after World War II in Japan linked coffee to reductions in liver and pancreatic cancer in men, and liver, colon and endometrial cancer in women. The authors speculated that coffee could reduce resistance to insulin, “and may thereby reduce the risk of diabetes-related cancers such as colon, liver, pancreas and endometrium.”

A matter of the heart

A 2010 study¹³ of 37,514 Dutch people found a slight benefit for coffee in heart disease: People who drank two to three cups a day had only 79 percent the rate of heart disease as abstainers, but the reduction was not statistically significant. Above 4 cups per day, the rate returned close to the no-coffee rate. Coffee did not affect the rate of strokes.

However, Swedish researchers studied¹⁴ people after a heart attack, and found that drinking one to three cups of coffee reduced the odds of dying to 68 percent of the risk for abstainers.

We put down our coffee mug with a jittery hand, wondered whether swilling coffee could harm the heart, and phoned Richard Page, a professor of medicine at the University of Wisconsin-Madison. Page, an expert in arrhythmias – the irregular heart rhythms that can cause deadly heart attacks – said, “It’s hard to demonstrate a relationship between caffeine consumption and arrhythmias, but there are case reports. I see a number of patients with arrhythmias, particularly atrial fibrillation, and occasionally we see some relationship with excessive consumption of caffeine.”

Although Page was not alarmed by coffee, he was not so sure about the mega-doses that were linked to health benefits in some studies. “I would be cautious; I have heard of a couple of adolescents developing atrial fibrillation (a hard-to-treat arrhythmia) after taking monster energy drinks; I don’t think such high doses of caffeine are good for people.”

The bottom line

If Captain C seems helpful against some cancers, dementia and diabetes, is it guaranteed to extend your life? No. A European study¹⁵, for example, found that “Neither coffee nor tea consumption was associated with stroke or all-cause mortality.”

A long American study, using data from 41,736 men (followed for 18 years), and 86, 214 women (24 years), found a slight, significant trend toward fewer deaths from all causes; those who drank at least six cups a day had a death rate just 80 percent (men) to 83 percent (women) of the non-drinkers. The main benefit was a reduction in cardiovascular disease.

However, coffee consumption did not affect cancer deaths, after adjusting for factors like obesity and smoking, and the authors concluded, ¹⁶ “The possibility of a modest benefit of coffee consumption on all-cause and cardiovascular disease mortality needs to be further investigated.”

Not exactly a ringing endorsement, but then, did we promise a simple answer?

Would you like your triple-espresso with soy milk?