Everyone knows coffee is evil, right? Drinking coffee is associated with groggy smokers, stained teeth and short life spans spent commuting to miserable jobs that require a dose of caffeine to get through. Well, perhaps. There has been a lot of interesting research about how coffee or caffeine (and they are not the same thing) affects our health. Despite concerns for certain people and conditions, the news is not all that bad. Since coffee remains the single most popular beverage in the world, that is good news.
Reviewing the evidence, a cautionary tale develops about how difficult it can be to construct a good study and interpret the results. Readers also need to remember that the information provided depends in part on who is delivering it, who is paying for it and what they want you to hear. Here are a few points to keep in mind:
A study of caffeine is not the same as a study of coffee. This is a common problem with dietary studies: in an attempt to make the study more accurate, researchers might decide to isolate a single component from a food or beverage. The food itself, after all, will have variable quantities of that component. However, there can be very different results when consuming the whole food vs. an extracted part.
A “cup” of coffee is typically assumed to be 6 oz. – not your 16 oz. travel mug!
Caffeine levels are usually assumed to be about 100 mg per cup, but in fact vary significantly with the type of bean, brewing method, and even from batch to batch. Brewed coffee is estimated to range from 100-150 mg per cup, a similar volume of espresso having about 90 mg. Arabica beans have less caffeine than robusta beans.
Two health topics are commonly associated with coffee consumption – its effect on blood sugar and insulin resistance, and its effect on the adrenal glands. But there has also been considerable research on the consumption of coffee and the incidence of cancer,
Coffee and Diabetes Mellitus
When coffee drinkers over-indulge in sweets, many notice an immediate craving for coffee. The combination of coffee and dessert is common and traditional in many regions, as is the taking of bitter herbs (often in an alcoholic beverage) as a digestive aid. The desire to consume coffee together with sweet flavors could be due to coffee’s bitterness, but there may also be some beneficial effect on blood sugar levels that elicits a craving for coffee when blood sugar levels surge.
Some dieticians and researchers consider coffee detrimental to blood sugar levels because it (or the caffeine in it) stimulates the adrenal glands. This stimulation increases the production of hormones (adrenaline and glucagon) that cause the release of stored sugars into the blood . It is one of the ways a stimulant prepares the body for increased physical activity and higher energy demands.
There follows a supposition that sweetened coffee aggravates this effect by putting sugar into the blood, both via the digestive system and by releasing stored sugars through hormonal stimuli. When there is insufficient physical activity to consume the extra energy from the sugar, the pancreas responds by pumping out insulin. Insulin decreases sugar levels in the blood by driving it into the cells of the body – putting it back into storage. Physiologically, it’s like taking an “upper” and a “downer” at the same time, in a convoluted attempt to stay on an even keel.
There are concerns that the increased demand for insulin can lead to decreased sensitivity to it – as happens with Type 2 diabetes and metabolic syndrome. And there has been research indicating that caffeine (taken as an isolated drug) inhibits sugar metabolism.
However, a several studies in 2006 and 2004 indicate that coffee consumption is actually associated with a decreased incidence of Type 2 diabetes. Although any study has its weaknesses, these were conducted in different geographic areas, with different participants and different methodologies, and did their best to account for confounding factors such as obesity and smoking.
Coffee, Heart Health and the Adrenal Glands
The adrenal glands produce various hormones that are responsible for coordinating and monitoring a variety of physiological activities. These include cortisol, adrenaline, DHEA, estrogen and testosterone. There is concern that caffeine can cause the body to be flooded with excess adrenaline, resulting in an increased heart rate and higher blood pressure. Some authors even suggest that ongoing stimulation of the adrenal glands will eventually cause them “wear out.” Although there has been research into the stimulation caused by caffeine, an online search produced no study that addressed the “wearing out” theory.
A 2002 study from theDukeUniversityMedicalCenter investigated the effects of moderate doses of caffeine on blood pressure and heart rate, urinary excretion of epinephrine, norepinephrine, and cortisol, and self-reported stress during normal activities. This study found that caffeine raised average blood pressure during the workday and evening by 4/3 mm Hg and increased average heart rate by 2 bpm. Caffeine also caused a 32% increase in the levels of epinephrine (a stimulating hormone). In addition, caffeine amplified the increases in blood pressure and heart rate associated with higher levels of stress from daily activities. These effects were undiminished through the evening until bedtime. An Australian study also found that while most data suggest very little excess risk of coronary heart disease among the general population of habitual coffee drinkers, the better controlled data suggest an excess risk on the order of 60% for people drinking five or more cups per day.
In another area of concern, a 2004 study linked moderate to high levels of coffee consumption to increased inflammatory markers. Inflammatory markers are important as predictors of coronary heart disease. Another study published in 2004 found that the combination of caffeine plus smoking cigarettes reduced the flexibility of the aorta more than either substance alone.
However, other work has suggested that response to coffee vs. isolated caffeine is minimal, particularly for habitual drinkers. In 2006, a study was reported in the April 24th Rapid Access issue of Circulation. The authors concluded that “coffee consumption was not associated with an increased risk of Coronary Heart Disease.” This study found that total cholesterol, low-density and high-density lipoprotein cholesterol levels in men and women coffee drinkers did not differ in those who drank caffeinated or decaffeinated coffee. CHD risk associated with drinking coffee did not differ in people with or without type 2 diabetes.
So are you off the hook? Er… not so fast. A 2006 study published in the Journal of the American Medical Association found that some people have a genetic mutation of the CYP1A2 enzyme that reduces the rate they metabolize caffeine. For those people, drinking four or more cups a day over for a year had a 64% increased risk of heart attack, compared to less than 1% increased risk for people without the gene mutation. Such genetic differences between participants in a study may explain why it has been hard to determine if there is a clear association between coffee consumption and heart attack risk.
Organ damage and cancer
This section will briefly list some research on coffee consumption and how it affects various organs and/or its association with different types of cancer.
A study of cellular changes in the pancreas in 1986 found no changes due to coffee drinking. Most studies do not support an association between coffee consumption and pancreatic cancer.
A study of gastric cancer conducted in Spain from 1987-1989 found no association with smoking, or with the consumption of coffee or tea.
In a Polish study of stomach cancer published in 1999, no association was found with drinking regular coffee or herbal tea or using milk/cream in coffee or tea. (The findings did confirm an association with cigarette smoking, which is estimated to account for approximately 20% of stomach cancers.)
A 2002 study published in the European Journal of Cancer Prevention found that coffee is associated only weakly or not at all with bladder cancer risk, inversely with colon cancer risk, and inconsistently with rectal cancer risk. Rectal cancer risk was not associated with either coffee or tea.
A HarvardMedicalSchool review of existing literature in 2002 found no convincing evidence has been presented to show that caffeine consumption increases the risk of any reproductive adversity in women.
In 2002, an evaluation was conducted of several lifestyle factors influencing benign prostatic (prostate) enlargement and the severity of benign prostatic hyperplasia (BPH). There was a strong inverse association between alcohol intake and men treated surgically for BPH or in ‘watchful waiting’ for surgical intervention, but a positive correlation with coffee consumption. (That is, coffee seemed to make the conditions worse, alcohol was associated with improvements.) The authors concluded that “Given the opposite effects of coffee and moderate alcohol consumption, together with the increased risk for clinical BPH in men with coronary heart disease, coffee constituents, which increase the serum concentration of low-density lipoprotein cholesterol, may be involved in the pathophysiology of BPH.”
The news is also not good for the urinary tract. A study in The Netherlands in 2002 concluded that, in accordance with earlier reviews, coffee consumption increases the risk of urinary tract cancer by approximately 20%. The consumption of tea seems not to be related to an increased risk of urinary tract cancer. There is also evidence that caffeine intake at a level equivalent to two or more cups of coffee daily produces increased calcium in the urine, which suggests a higher risk of kidney stones (a study that looked at coffee, rather than caffeine, consumption and calcium in the urine could not be found).
Coffee and Bone Mass
A 1991 study of 619 elderly men and women in Sweden concluded that coffee drinking was not a contributory independent risk factor for loss of bone mass and fractures.
There has been enough conflicting information and supposition published that individuals may be tempted to pick and choose data that supports the answer they were hoping for. Overall, it does seem that light to moderate coffee consumption (less than four 6 oz. cups a day) is not particularly bad for you. However, consumption should be limited for those particularly sensitive to caffeine (suggesting a reduced ability to metabolize it) and those concerned about urinary tract and/or prostrate health. As with so many things, moderation is definitely appropriate.
Also, there is little doubt that coffee/caffeine is addictive, and that’s never a good sign. Researchers at JohnsHopkinsUniversity in Baltimore found that as little as one cup of coffee a day can produce caffeine addiction. When you then try to do without it, you may suffer a range of withdrawal symptoms, including headache, fatigue and difficulty concentrating. Some may even feel as though they have the flu, with nausea and muscle pain. Simple caffeine withdrawal may explain much of the malaise associated with “cleansing diets.” To help reduce your coffee and/or caffeine intake it can be helpful to begin substituting decaffeinated versions (use products decaffeinated by the “Swiss” water method, which does not add chemicals to beans). Tea also seems to be less aggravating to the body’s systems, and has some benefits of its own; it may be worth switching over, and just saying goodbye to coffee.