Coffee lovers around the world who reach for their favorite morning brew probably aren’t thinking about its health benefits or risks. And yet this beverage has been subject to a long history of debate. In 1991 coffee was included in a list of possible carcinogens by the World Health Organization. By 2016 it was exonerated, as research found that the beverage was not associated with an increased risk of cancer; on the contrary, there was a decreased risk of certain cancers among those who drink coffee regularly once smoking history was properly accounted for. Additional accumulating research suggests that when consumed in moderation, coffee can be considered a healthy beverage. Why then in 2018 did one U.S. state pass legislation that coffee must bear a cancer warning label? Read on to explore the complexities of coffee.
- Vitamin B2 (riboflavin)
- Plant chemicals: polyphenols including chlorogenic acid and quinic acid, and diterpenes including cafestol and kahweol
One 8-ounce cup of brewed coffee contains about 95 mg of caffeine. A moderate amount of coffee is generally defined as 3-5 cups a day, or on average 400 mg of caffeine, according to the Dietary Guidelines for Americans.
Coffee and Health
Coffee is an intricate mixture of more than a thousand chemicals.  The cup of coffee you order from a coffee shop is likely different from the coffee you brew at home. What defines a cup is the type of coffee bean used, how it is roasted, the amount of grind, and how it is brewed. Human response to coffee or caffeine can also vary substantially across individuals. Low to moderate doses of caffeine (50–300 mg) may cause increased alertness, energy, and ability to concentrate, while higher doses may have negative effects such as anxiety, restlessness, insomnia, and increased heart rate.  Still, the cumulative research on coffee points in the direction of a health benefit. [3,4] Does the benefit stem from the caffeine or plant compounds in the coffee bean? Is there a certain amount of coffee needed a day to produce a health benefit?
Coffee may affect how cancer develops, ranging from the initiation of a cancer cell to its death. For example, coffee may stimulate the production of bile acids and speed digestion through the colon, which can lower the amount of carcinogens to which colon tissue is exposed. Various polyphenols in coffee have been shown to prevent cancer cell growth in animal studies. Coffee has also been associated with decreased estrogen levels, a hormone linked to several types of cancer.  Caffeine itself may interfere with the growth and spread of cancer cells.  Coffee also appears to lower inflammation, a risk factor for many cancers.
The 2018 uproar in California due to warning labels placed on coffee products stemmed from a chemical in the beverage called acrylamide, which is formed when the beans are roasted. Acrylamide is also found in some starchy foods that are processed with high heat like French fries, cookies, crackers, and potato chips. It was classified in the National Toxicology Program’s 2014 Report on Carcinogens, as “reasonably anticipated to be a human carcinogen” based on studies in lab animals. However, there is not yet evidence of a health effect in humans from eating acrylamide in food. Regardless, in March 2018 a California judge ruled that all California coffee sellers must warn consumers about the “potential cancer risk” from drinking coffee, because coffee-selling companies failed to show that acrylamide did not pose a significant health risk. California’s law Proposition 65, or The Safe Drinking Water and Toxic Enforcement Act of 1986, fueled the ruling, which requires a warning label to be placed on any ingredient from a list of 900 confirmed or suspected carcinogens.
However, many cancer experts disputed the ruling, stating that the metabolism of acrylamide differs considerably in animals and humans, and the high amount of acrylamide used in animal research is not comparable to the amount present in food. They cited the beneficial health effects of coffee, with improved antioxidant responses and reduced inflammation, both factors important in cancer prevention. Evidence from the American Institute for Cancer Research concludes that drinking coffee may reduce risk for endometrial and liver cancer, and based on a systematic review of a large body of research, it is not a risk for the cancers that were studied.
In June 2018, the California Office of Environmental Health Hazard Assessment (OEHHA) proposed a new regulation exempting coffee from displaying cancer warnings under Proposition 65. This proposal was based on a review of more than 1,000 studies published by the World Health Organization’s International Agency for Research on Cancer that found inadequate evidence that drinking coffee causes cancer. In January 2019, OEHHA completed its review and response to comments and submitted the regulation to the Office of Administrative Law (OAL) for final review.
Type 2 Diabetes
Although ingestion of caffeine can increase blood sugar in the short-term, long-term studies have shown that habitual coffee drinkers have a lower risk of developing type 2 diabetes compared with non-drinkers. The polyphenols and minerals such as magnesium in coffee may improve the effectiveness of insulin and glucose metabolism in the body.
- In a meta-analysis of 45,335 people with type 2 diabetes followed for up to 20 years, an association was found with increasing cups of coffee and a lower risk of developing diabetes. Compared with no coffee, the decreased risk ranged from 8% with 1 cup a day to 33% for 6 cups a day. Caffeinated coffee showed a slightly greater benefit than decaffeinated coffee. 
- Another meta-analysis of prospective cohort studies showed similar associations. When comparing the highest intake of coffee (up to 10 cups a day) with the lowest (<1 cup), there was a 30% decreased risk of type 2 diabetes in those drinking the highest amounts of coffee and caffeine and a 20% decreased risk when drinking decaffeinated coffee. Further analysis showed that the incidence of diabetes decreased by 12% for every 2 extra cups of coffee a day, and 14% for every 200 mg a day increase in caffeine intake (up to 700 mg a day). 
Caffeine is a stimulant affecting the central nervous system that can cause different reactions in people. In sensitive individuals, it can irritate the stomach, increase anxiety or a jittery feeling, and disrupt sleep. Although many people appreciate the temporary energy boost after drinking an extra cup of coffee, high amounts of caffeine can cause unwanted heart palpitations in some.
Unfiltered coffee, such as French press and Turkish coffees, contains diterpenes, substances that can raise bad LDL cholesterol and triglycerides. Espresso coffee contains moderate amounts of diterpenes. Filtered coffee (drip-brewed coffee) and instant coffee contain almost no diterpenes as the filtering and processing of these coffee types removes the diterpenes.
Despite these factors, evidence suggests that drinking coffee regularly may lower the risk of heart disease and stroke:
- Among 83,076 women in the Nurses’ Health Study, drinking 4 or more cups of coffee each day was associated with a 20% lower risk of stroke compared with non-drinkers. Decaffeinated coffee also showed an association, with 2 or more cups daily and a 11% lower stroke risk. The authors found no such association with other caffeinated drinks such as tea and soda. These coffee-specific results suggest that components in coffee other than caffeine may be protective. 
- A large cohort of 37,514 women concluded that moderate coffee drinking of 2-3 cups a day was associated with a 21% reduced risk of heart disease. 
- In addition, a meta-analysis of 21 prospective studies of men and women looking at coffee consumption and death from chronic diseases found a link between moderate coffee consumption (3 cups per day) and a 21% lower risk of cardiovascular disease deaths compared with non-drinkers. 
- Another meta-analysis of 36 studies including men and women reviewed coffee consumption and risk of cardiovascular diseases (including heart disease, stroke, heart failure, and deaths from these conditions). It found that when compared with the lowest intakes of coffee (average 0 cups), a moderate coffee intake of 3-5 cups a day was linked with a 15% lower risk of cardiovascular disease. Heavier coffee intake of 6 or more cups daily was neither associated with a higher nor a lower risk of cardiovascular disease. 
Naturally occurring polyphenols in both caffeinated and decaffeinated coffee can act as antioxidants to reduce damaging oxidative stress and inflammation of cells. It may have neurological benefits in some people and act as an antidepressant.  Caffeine may affect mental states such as increasing alertness and attention, reducing anxiety, and improving mood.  A moderate caffeine intake of less than 6 cups of coffee per day has been associated with a lower risk of depression and suicide. However in a few cases of sensitive individuals, higher amounts of caffeine may increase anxiety, restlessness, and insomnia. Suddenly stopping caffeine intake can cause headache, fatigue, anxiety, and low mood for a few days and may persist for up to a week. 
- A prospective cohort study following 263,923 participants from the National Institutes of Health and American Association of Retired Persons found that those who drank 4 or more cups of coffee a day were almost 10% less likely to become depressed than those who drank none. 
- In a meta-analysis of observational studies including 330,677 participants, the authors found a 24% reduced risk of depression when comparing the highest (4.5 cups/day) to lowest (<1 cup) intakes of coffee. They found an 8% decreased risk of depression with each additional cup of coffee consumed. There was also a 28% reduced risk of depression comparing the highest to lowest intakes of caffeine, with the greatest benefit occurring with caffeine intakes between 68 and 509 mg a day (about 6 oz. to 2 cups of coffee). 
- A review looking at three large prospective cohorts of men and women in the U.S. found a decreasing risk of suicide with increasing coffee consumption. When compared with no-coffee drinkers, the pooled risk of suicide was 45% lower among those who drank 2-3 cups daily and 53% lower among those who drank 4 or more cups daily. There was no association between decaffeinated coffee and suicide risk, suggesting that caffeine was the key factor, rather than plant compounds in coffee. 
- Parkinson’s disease (PD) is mainly caused by low dopamine levels. There is consistent evidence from epidemiologic studies that higher consumption of caffeine is associated with lower risk of developing PD. The caffeine in coffee has been found in animal and cell studies to protect cells in the brain that produce dopamine.
- A systematic review of 26 studies including cohort and case-control studies found a 25% lower risk of developing PD with higher intakes of caffeinated coffee. It also found a 24% decreased risk with every 300 mg increase in caffeine intake. 
- A Finnish cohort study tracked coffee consumption and PD development in 6,710 men and women over 22 years. In that time, after adjusting for known risks of PD, those who drank at least 10 cups of coffee a day had a significantly lower risk of developing the disease than non-drinkers. 
- A large cohort of men and women were followed for 10 and 16 years, respectively, to study caffeine and coffee intake on PD. The results showed an association in men drinking the most caffeine (6 or more cups of coffee daily) and a 58% lower risk of PD compared with men drinking no coffee. Women showed the lowest risk when drinking moderate intakes of 1-3 cups coffee daily. 
- Alzheimer’s disease: In the CAIDE (Cardiovascular Risk Factors, Aging and Dementia) study, drinking 3-5 cups of coffee a day at midlife (mean age 50 years) was associated with a significantly decreased risk of Alzheimer’s disease later in life compared with low coffee drinkers after 21 years of follow-up. 
- However, three systematic reviews were inconclusive about coffee’s effect on Alzheimer’s disease due to a limited number of studies and a high variation in study types that produced mixed findings. Overall the results suggested a trend towards a protective effect of caffeine against late-life dementia and Alzheimer’s disease, but no definitive statements could be made. The authors stated the need for larger studies with longer follow-up periods. Randomized controlled trials studying a protective effect of coffee or caffeine on the progression of Alzheimer’s disease and dementia are not yet available. [21-23]
There are various proposed actions of caffeine or components in coffee that may prevent the formation of gallstones. The most common type of gallstone is made of cholesterol. Coffee may prevent cholesterol from forming into crystals in the gallbladder. It may stimulate contractions in the gallbladder and increase the flow of bile so that cholesterol does not collect. 
A study of 46,008 men tracked the development of gallstones and their coffee consumption for 10 years. After adjusting for other factors known to cause gallstones, the study concluded that men who consistently drank coffee were significantly less likely to develop gallstones compared to men who did not.  A similar large study found the same result in women. 
- In a large cohort of more than 200,000 participants followed for up to 30 years, an association was found between drinking moderate amounts of coffee and lower risk of early death. Compared with non-drinkers, those who drank 3-5 cups of coffee daily were 15% less likely to die early from all causes, including cardiovascular disease, suicide, and Parkinson’s disease. Both caffeinated and decaffeinated coffee provided benefits. The authors suggested that bioactive compounds in coffee may be responsible for interfering with disease development by reducing inflammation and insulin resistance. 
- In a large prospective cohort of more than 500,000 people followed for 10 years, an association was found between drinking higher amounts of coffee and lower rates of death from all causes. Compared with non-drinkers, those drinking 6-7 cups daily had a 16% lower risk of early death.  A protective association was also found in those who drank 8 or more cups daily. The protective effect was present regardless of a genetic predisposition to either faster or slower caffeine metabolism. Instant and decaffeinated coffee showed a similar health benefit.
The bottom line: A large body of evidence suggests that consumption of caffeinated coffee does not increase the risk of cardiovascular diseases and cancers. In fact, consumption of 3 to 5 standard cups of coffee daily has been consistently associated with a reduced risk of several chronic diseases.  However, some individuals may not tolerate higher amounts of caffeine due to symptoms of jitteriness, anxiety, and insomnia. Specifically, those who have difficulty controlling their blood pressure may want to moderate their coffee intake. Pregnant women are also advised to aim for less than 200 mg of caffeine daily, the amount in 2 cups of coffee, because caffeine passes through the placenta into the fetus and has been associated with pregnancy loss and low birth weight. [3, 27] Because of the potential negative side effects some people experience when drinking caffeinated coffee, it is not necessary to start drinking it if you do not already or to increase the amount you currently drink, as there are many other dietary strategies to improve your health. Decaffeinated coffee is a good option if one is sensitive to caffeine, and according to the research summarized above, it offers similar health benefits as caffeinated coffee. It’s also important to keep in mind how you enjoy your brew. The extra calories, sugar, and saturated fat in a coffee house beverage loaded with whipped cream and flavored syrup might offset any health benefits found in a basic black coffee.
What about iced coffee?
Coffee beans are the seeds of a fruit called a coffee cherry. Coffee cherries grow on coffee trees from a genus of plants called Coffea. There are a wide variety of species of coffee plants, ranging from shrubs to trees.
- Type of bean. There are two main types of coffee species, Arabica and Robusta. Arabica originates from Ethiopia and produces a mild, flavorful tasting coffee. It is the most popular type worldwide. However, it is expensive to grow because the Arabica plant is sensitive to the environment, requiring shade, humidity, and steady temperatures between 60-75 degrees Fahrenheit. The Robusta coffee plant is more economical to grow because it is resistant to disease and survives in a wider range of temperatures between 65-97 degrees Fahrenheit. It can also withstand harsh climate changes such as variations in rainfall and strong sunlight.
- Type of roast. Coffee beans start out green. They are roasted at a high heat to produce a chemical change that releases the rich aroma and flavor that we associate with coffee. They are then cooled and ground for brewing. Roasting levels range from light to medium to dark. The lighter the roast, the lighter the color and roasted flavor and the higher its acidity. Dark roasts produce a black bean with little acidity and a bitter roasted flavor. The popular French roast is medium-dark.
- Type of grind. A medium grind is the most common and used for automatic drip coffee makers. A fine grind is used for deeper flavors like espresso, which releases the oils, and a coarse grind is used in coffee presses.
Decaffeinated coffee. This is an option for those who experience unpleasant side effects from caffeine. The two most common methods used to remove caffeine from coffee is to apply chemical solvents (methylene chloride or ethyl acetate) or carbon dioxide gas. Both are applied to steamed or soaked beans, which are then allowed to dry. The solvents bind to caffeine and both evaporate when the beans are rinsed and/or dried. According to U.S. regulations, at least 97% of the caffeine must be removed to carry the decaffeinated label, so there may be trace residual amounts of caffeine. Both methods may cause some loss of flavor as other naturally occurring chemicals in coffee beans that impart their unique flavor and scent may be destroyed during processing.
Watch out for hidden calories in coffee drinks
A plain “black” cup of coffee is a very low calorie drink—8 ounces only contains 2 calories! However, adding sugar, cream, and milk can quickly bump up the calorie counts. A tablespoon of cream contains 52 calories, and a tablespoon of whole milk contains 9 calories. While 9 calories isn’t a lot, milk is often poured into coffee without measuring, so you may be getting several servings of milk or cream in your coffee. A tablespoon of sugar contains 48 calories, so if you take your coffee with cream and sugar, you’re adding over 100 extra calories to your daily cup.
However, the real caloric danger occurs in specialty mochas, lattes, or blended ice coffee drinks. These drinks are often super-sized and can contain anywhere from 200-500 calories, as well as an extremely large amount of sugar. With these drinks, it’s best to enjoy them as a treat or dessert, and stick with plain, minimally sweetened coffee on a regular basis
- Place beans or ground coffee in an airtight opaque container at room temperature away from sunlight. Inside a cool dark cabinet would be ideal. Exposure to moisture, air, heat, and light can strip coffee of its flavor. Coffee packaging does not preserve the coffee well for extended periods, so transfer larger amounts of coffee to airtight containers.
- Coffee can be frozen if stored in a very airtight container. Exposure to even small amounts of air in the freezer can lead to freezer burn.
- Follow directions on the coffee package and your coffee machine, but generally the ratio is 1-2 tablespoons of ground coffee per 6 ounces of water.
- For optimal coffee flavor, drink soon after brewing. The beverage will lose flavor with time.
- Use ground coffee within a few days and whole beans within two weeks.
Did You Know?
- It is a myth that darker roasts contain a higher level of caffeine than lighter roasts. Lighter roasts actually have a slightly higher concentration!
- Coffee grinds should not be brewed more than once. Brewed grinds taste bitter and may no longer produce a pleasant coffee flavor.
- While water is always the best choice for quenching your thirst, coffee can count towards your daily fluid goals. Although caffeine has a mild diuretic effect, it is offset by the total amount of fluid from the coffee.
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