March 2018 Issue

The Power of Coffee
By Judith C. Thalheimer, RD, LDN
Today's Dietitian
Vol. 20, No. 3, P. 20

Research shows correlations between consumption and various aspects of health.

Coffee is one of the most commonly consumed beverages in the world, and its popularity in America is on the rise.1,2 In 2017, 62% of Americans reported drinking coffee on a daily basis, up from 57% in 2016.2 When something is so widely and frequently consumed, even small health effects can be important on a population scale.1 Fortunately, several recent review studies on the safety and health impact of coffee drinking show that this upward trend may be beneficial. Analysis suggests that drinking several cups of coffee every day is, in most cases, likely to do more good than harm.1

What's in the Cup
Coffee beans are the seeds from a fruit called a coffee cherry.3 The fruit is either dried or pulped to release the beans, which are then hulled, polished, graded, sorted by size and weight, and evaluated by professional coffee tasters (cuppers) before being roasted to 400° F.3 The roasting releases the oil caffeol, producing that familiar aroma and flavor.3 The roasted beans are ground and used to create an infusion, the chemical makeup of which depends on a wide range of factors, from the plant species (Coffea arabica or C canephora [robusta]), degree of roasting, and grind setting to whether it's filtered or unfiltered, decaffeinated or regular, boiled, steeped, or brewed under pressure.1,4 The addition of other ingredients (such as cream and sugar) also impacts coffee's nutrient profile.1,4 What's more, two people drinking the same coffee may have different responses, as genotype and gut microbiome determine which coffee metabolites are available and how they're utilized.1

Although mostly known for its caffeine content, coffee is a complex mix of carbohydrates, lipids, amino acids, vitamins, minerals, and a wide range of phytochemicals. "Coffee is known to be a complex mixture of more than 1,000 bioactive compounds that may have beneficial antioxidant, anti-inflammatory, antifibrotic, and anticancer properties," says Robin Poole, MB ChB, MRCGP, PGCert, MSc, MFPH, a physician and public health doctor at the University of Southampton in England. "Coffee contains much higher amounts of antioxidants in a typical serving compared with tea, and, for people who drink coffee, it may be one of the major sources of antioxidants in their diet, perhaps even higher than fruits and vegetables."

Researchers have studied many of the active compounds in coffee. "The compounds we know most about are caffeine, chlorogenic acids, and diterpenes," Poole says. Caffeine is an alkaloid that generally stimulates the central nervous system, but it also has significant antioxidant properties.1,4 (The decaffeination process, therefore, decreases the antioxidant potential of coffee.)4 But caffeine alone doesn't account for coffee's health benefits. "There may be a synergy between caffeine and the other ingredients, which is why noncoffee caffeine doesn't appear to have the same beneficial effects as coffee," Poole says.

Coffee is one of the richest dietary sources of chlorogenic acids. These compounds are powerful antioxidants in lab tests, but that doesn't necessarily mean they give coffee its health-boosting benefits. Researchers still don't know how strong the activity of these antioxidants is once they've been metabolized.4 In addition, the roasting process degrades the key chlorogenic acid in coffee, but one of the compounds released from this breakdown is caffeic acid, a phenolic compound that's an antioxidant in its own right.1,4 Other antioxidant phenolic compounds, such as tannins, lignans, and anthocyanins, are found in coffee in lesser amounts.4

The diterpenes found in coffee (cafestol and kahweol) have anticarcinogenic effects.1 Unfortunately, these fat-soluble compounds also have been found to raise total and LDL cholesterol levels.4 This is of particular concern with unfiltered coffee (Scandinavian boiled coffee, Turkish coffee, and French press coffee) and coffee beans eaten whole (as with chocolate-covered beans). Filtered, percolated, and instant coffees have much lower levels.4

The antioxidant and anticancer effects of these and other compounds, along with anti-inflammatory and antibiotic potential, have led researchers to examine coffee's impact on all-cause mortality, cancer, cardiovascular and metabolic diseases, as well as diseases of the neurological, musculoskeletal, and gastrointestinal systems, and the liver.1

Latest on Coffee and Health
In November 2017, The BMJ published an umbrella review of meta-analyses that was designed to assess all of the existing evidence of the effects of coffee consumption on health. "The umbrella review assimilated the vast body of existing higher-level evidence for associations of coffee drinking and multiple health outcomes," according to Poole, who's lead author of the review. "The intention was to identify potential harms before we progress to a more definitive randomized controlled trial in the future in which coffee could be given as a potential treatment." The review included data from 201 meta-analyses of observational research on a wide range of conditions. It also analyzed 17 meta-analyses of randomized controlled trials with outcomes related to blood pressure, cholesterol, triglycerides, and pregnancy.1 "The great news was that aside from pregnancy, drinking coffee was more frequently associated with benefit than harm," Poole says.

The BMJ umbrella analysis discusses the effects of "high" vs "low" coffee intake. It's important to note that there was no consistent definition of what constituted "high" vs "low" intake across the original meta-analyses reviewed. In some studies, "high" intake could be two cups and more, while in others it was six. But Poole and his colleagues found that the results were statistically stable when analyzed in several different ways: The same associations between coffee intake and health outcomes were found when looking at "any vs none" and when using linear dose-response analysis (ie, whether adding one more cup of coffee increased the response). "The stability of results across different exposure categories suggests that the 'high' vs 'low' comparison does represent a reasonable differential even if it is comparing ranges of exposures," Poole says.

All-Cause Mortality
Consumption of both caffeinated and decaffeinated coffee was associated with lower all-cause mortality.1 An August 2017 study in the Annals of Internal Medicine concluded that this finding holds true for people of many races and ethnicities, including African Americans, Japanese Americans, and Latinos.5 The authors of the umbrella analysis report that the largest benefit to all-cause mortality was seen at "three cups a day." It's important to note that, for this and all other outcomes, the analysis couldn't offer a standard measure for what constitutes a "cup."

"Unfortunately, we cannot be specific because the cup size and preparation method would often not be recorded in the original studies that made up each meta-analysis included in our umbrella review," Poole says. "This is because most dietary assessment tools would have simply asked only for the number of cups of coffee consumed each day without more specific details. This type of variation would most likely affect those with and without a specific disease equally, and is statistically more likely to dilute associations than strengthen them, so finding consistent beneficial associations is reassuring. We are not, however, making any recommendations for a target intake."

While some people may assume that the stimulant effect of caffeine is bad for the heart, the data suggest the opposite may be true. "Coffee drinking was associated not only with a lower risk of death from any cause, but also death from CVD, or getting CVD in the first place," Poole says. "The greatest reduction in risk for these health outcomes was seen at intakes of three to four cups of coffee a day." Overall, people who reported drinking three cups of coffee a day (of any size) had a 19% lower risk of dying from CVD, a 16% lower risk of death from coronary heart disease, and a 30% lower risk of death from stroke than nondrinkers. Benefits were less pronounced for people who reported drinking more than three cups per day, but no harm was seen.

An area of concern is high blood pressure: A review published in January 2018 supported the conclusion that consuming coffee is associated with lower risk of CVD and all-cause mortality, even in people who previously have suffered a CVD event, but the authors caution that people with uncontrolled high blood pressure should avoid consuming large doses of caffeine.6 Fortunately, the umbrella review found that drinking decaffeinated coffee also was associated with lower risk of dying from CVD.1

On the down side, consumption of unfiltered (boiled, Turkish, or French press) coffee seems consistently associated with unfavorable changes in cholesterol and triglyceride levels. In a meta-analysis of randomized controlled trials, total cholesterol, LDL cholesterol, and triglyceride levels were significantly higher in unfiltered coffee drinkers than in controls. Similar significant changes in LDL cholesterol and triglycerides weren't seen in people who drank either coffee brewed using a filter or decaf coffee.1

Drinking coffee, especially caffeinated coffee, was found to be associated with lower cancer risk. This association typically is attributed to the antioxidant effects of the compounds in coffee, although the exact mechanisms underlying these effects are unknown. "We found associations with lower risk of incident cancer, and also specific cancers," Poole says. Drinking caffeinated coffee was associated with lower incidence of prostate cancer, endometrial cancer, melanoma, oral cancer, leukemia, nonmelanoma skin cancer, and liver cancer.1 Coffee may increase lung cancer risk in smokers but could reduce risk slightly in people who never have smoked.1 Decaffeinated coffee wasn't significantly associated with cancer mortality, but drinking decaf does seem to lower endometrial cancer risk, and there was a small beneficial association between decaf and lung cancer.1

Metabolic Disease
Coffee drinkers, whether they choose decaf or regular, appear to have a decreased risk of developing type 2 diabetes.1 As cups per day increased from one cup to six cups, risk of diabetes declined.1 Higher intake was associated with a 9% lower risk of metabolic syndrome compared with lower intake.1 Risk of gout also decreases as coffee consumption increases.1

Liver and Gastrointestinal System
Any amount of coffee drinking appears to be good for the liver. "Coffee drinking was consistently associated with benefit in liver conditions including lower risk of chronic liver disease, fibrosis, cirrhosis, and liver cancer," Poole says. The BMJ review found a 29% lower risk of nonalcoholic fatty liver disease, a 27% lower risk of liver fibrosis, and a 39% lower risk of liver cirrhosis. The authors reported that the evidence for positive effects of coffee drinking on liver conditions is stronger than findings in any other category studied.1 Risk of gallstones also consistently appears to decline as coffee intake increases.1 High intake of coffee may slightly increase risk of gastroesophageal reflux disease (GERD), but results aren't significant.1

Musculoskeletal System
Results concerning coffee and risk of bone fracture are mixed. The BMJ analysis found no significant overall associations between coffee drinking and risk of fractures; however, breaking down results by sex tells a different story.1 "There was an increased risk of fracture in women but not in men," Poole says. It has been proposed that caffeine may influence calcium absorption and bone mineral density, but a recent comprehensive review found no effect of caffeine on bone health at levels equivalent to around four cups of coffee per day (400 mg caffeine).1

Consumption of coffee was consistently associated with a lower risk of Parkinson's disease, although the effect was significant only with caffeinated coffee.1 Coffee drinkers also may have lower risk of depression and Alzheimer's disease.1

One of the few situations in which drinking coffee seems to have the potential to be harmful is during pregnancy. "Coffee drinking in pregnancy was associated with increased risk of low birth weight and miscarriage," Poole says. "This is not new information, and existing advice to limit caffeine in pregnancy remains important." Pregnant women who drank the most coffee in studies had a higher risk of delivering a low-birth weight baby, losing the pregnancy, or experiencing first trimester preterm birth and second trimester preterm birth than women who drank the least.1 Coffee drinking hasn't been tied to third trimester preterm birth, neural tube defects, cleft palate, or cardiovascular system malformations.1 However, drinking coffee during pregnancy also appears to raise the risk of childhood leukemia, with highest risk in children of women who drank the most coffee.1

There are several possible reasons for the potential dangers of caffeine in pregnancy. The half-life of caffeine doubles during pregnancy, so the relative dose of caffeine from one cup of coffee is much higher in pregnant women.1 Moreover, caffeine crosses the placenta, and the fetus has low levels of enzymes to break it down.1 A 2017 systematic review and meta-analysis in Clinical Epidemiology concluded that, although there are risks in pregnancy, there seems to be little, if any, association between coffee/caffeine consumption and the ability to conceive.7 The World Health Organization advises a limit of two to three cups of coffee (200 to 300 mg caffeine) per day for pregnant women.7 The authors of the Clinical Epidemiology study feel this may be too high.7

Making Recommendations
Although coffee appears to have numerous health benefits, that doesn't mean nutrition professionals should encourage everyone to drink it. "It's important to keep in mind that, while there may be populationwide positive health associations with a particular food, any nutrition advice has to work for the individual," says Jen Bruning, MS, RDN, LDN, a spokesperson for the Academy of Nutrition and Dietetics. "Regular coffee can increase energy and alertness, but some people may have anxiety that's ramped up by caffeine. Likewise, coffee may not be the best choice for people with GERD or sleep issues." In addition, as stated above, pregnant women should be cautioned to limit coffee intake, as should women at risk of fractures and individuals with uncontrolled high blood pressure. Eating whole coffee beans or drinking unfiltered coffee can impact blood lipid levels. Even if none of these issues is of concern, drinking coffee isn't for everyone. "There's no reason why anyone needs to start drinking coffee if they don't already, especially if it's not something they enjoy," Bruning says.

The 2015–2020 Dietary Guidelines for Americans support moderate coffee consumption, defined as up to three to five 8-oz cups per day (providing up to 400 mg per day of caffeine), which is in line with recent research findings.8 Most people who drink coffee in any amount can be assured that coffee itself isn't harmful and may even be beneficial to their health. Clients should, however, keep in mind that the health effects of coffee can be impacted by other factors. "People need to be cautious around fancy, elaborate coffee drinks," Bruning says. "These typically have added fat and a lot of added sugar in the form of flavored syrups, not to mention the extra calories. For a change from a plain cup of coffee, a low-fat cappuccino or latte is a great way to go. They provide that coffee flavor, a caffeine boost, and some protein and calcium in the milk. Dusting with cinnamon or cocoa powder gives flavor without the fat, sugar, and calories." People also should be counseled to watch what they eat with their coffee, since cakes and cookies are popular but unhealthful choices.

"If people are already drinking coffee, they should continue to enjoy it," Poole says, "but try to keep it as healthful as possible."

— Judith C. Thalheimer, RD, LDN, is a nutrition writer and speaker based in Philadelphia, Pennsylvania.

1. Poole R, Kennedy OJ, Roderick P, Fallowfield JA, Hayes PC, Parkes J. Coffee consumption and health: umbrella review of meta-analyses of multiple health outcomes. BMJ. 2017;359:j5024.

2. National Coffee Association USA. Daily coffee consumption up sharply. Published March 25, 2017.

3. 10 steps from seed to cup. National Coffee Association USA website.

4. Higdon J. Coffee. Oregon State University Linus Pauling Institute Micronutrient Information Center website. Updated June 2017.

5. Park SY, Freedman ND, Haiman CA, Le Marchand L, Wilkens LR, Setiawan VW. Association of coffee consumption with total and cause-specific mortality among nonwhite populations. Ann Intern Med. 2017;167(4):228-235.

6. Rodríguez-Artalejo F, López-García E. Coffee consumption and cardiovascular disease: a condensed review of epidemiological evidence and mechanisms [published online January 10, 2018]. J Agric Food Chem. doi: 10.1021/acs.jafc.7b04506.

7. Lyngsø J, Ramlau-Hansen CH, Bay B, Ingerslev HJ, Hulman A, Kesmodel US. Association between coffee or caffeine consumption and fecundity and fertility: a systematic review and dose-response meta-analysis. Clin Epidemiol. 2017;9:699-719.

8. 2015–2020 Dietary Guidelines for Americans: answers to your questions. website. Updated January 7, 2016.