By Allison Becker, ND, LAc

Naturopathic Doctor, Acupuncturist in private practice in Evansville, WI

Dr. Becker reports no financial relationships relevant to this field of study.

SYNOPSIS: After rigorous evaluation using multiple statistics, an inverse relationship between coffee intake and all-cause mortality was demonstrated consistently across the racial/ethnic groups examined.

SOURCES: Gullar E, Blasco-Colmenares E, Arking DE, Zhao D. Moderate coffee intake can be part of a healthy diet. Ann Intern Med 2017;167:283-284.

Park SY, Freedman ND, Haiman CA, et al. Association of coffee consumption with total and cause-specific mortality among nonwhite populations. Ann Intern Med 2017;167:228-235.

Gunter MJ, Murphy N, Cross AJ, et al. Coffee drinking and mortality in 10 European countries: A multinational cohort study. Ann Intern Med 2017;167:236-247.

Travel throughout the world and one will find coffee to be one of the most popular drinks consumed. In the United States alone, about three-quarters of adults drink coffee and nearly half drink it daily.1 One also will find coffee bean preparations to vary tremendously depending on the coffee culture. From drip coffee to espresso, from light roast to dark, techniques vary widely and affect both the caffeine and antioxidant content of the beans. Frequently, coffee is consumed with added cream, milk, and/or sugar, which increase the caloric content significantly. Considering the quantity of coffee consumed worldwide, it is important for healthcare providers to study closely the potential health benefits of drinking coffee across culture and race.

Two large prospective cohort studies, the European Prospective Investigation into Cancer and Nutrition (EPIC) and the Multiethnic Cohort Study of Diet and Cancer (MEC), yielded data useful in analyzing the potential health benefits of coffee consumption. Uncontrolled confounding variables, such as smoking, pre-existing illness, alcohol intake, body mass index, and exercise, make it difficult to generalize the health benefits of coffee consumption. The authors of the EPIC and MEC trials attempted to control for confounding variables using multiple statistical methods.

EUROPEAN PROSPECTIVE INVESTIGATION INTO CANCER AND NUTRITION

The EPIC study included 521,330 people ≥ 35 years of age from 10 European countries. The intent was to evaluate whether coffee consumption was associated with all-cause and cause-specific mortality. The authors of this large study generated baseline data and followed up with participants an average of 16.4 years. Only two data points were generated: coffee consumption at baseline and 16.4 years later. Data generated included coffee consumption but also data for a subcohort including biomarkers for liver function, metabolism, and inflammation (ALT, AST, GGT, Alk Phos, C-reactive protein [CRP], high-density lipoprotein, lipoprotein (a), and hemoglobin A1c [HbA1c]). The researchers found that participants in the highest quartile of coffee consumption had a statistically significant lower risk of dying. This inverse association applied to both men and women.

How coffee is prepared before consumption varies widely in these European countries. For example, espresso is small in quantity but concentrated in phytochemicals. One serving of Italian espresso is not the same as one cup of coffee in the United Kingdom. Special statistics were used to account for these differences, using country-specific quartiles and looking at trends across exposure groups. Four quartiles of consumption were generated (low, medium-low, medium-high, and high). The authors analyzed the volume of coffee consumed (zero cups, less than one cup, one to less than two cups, two to less than three cups, more than three cups per day) with one cup = 237 mL coffee. Participants in the highest quartile of coffee consumption had a lower risk of death from all causes. Similar inverse associations and linear trends were found with caffeinated and decaffeinated coffee.

Multivariable models adjusted for body mass index, physical activity, smoking status (type, frequency, duration), education, menopausal status, use of oral contraceptives or hormone replacement therapy, alcohol consumption, total caloric intake per day, consumption of red and processed meats, and consumption of fruits and vegetables. When the data were adjusted for these variables, there continued to be an inverse association between mortality and coffee consumption.

All-cause mortality was recorded. Both men and women in the highest quartile of coffee consumption had a statistically significant decreased risk of dying from all gastrointestinal diseases (P trend < 0.001; hazard ratio [HR], 0.41 for men; HR, 0.60 for women). The gastrointestinal (GI) disease category included diseases of the oral cavity, esophagus, stomach, pancreas, gall bladder, liver, and intestines. More than one-third of the deaths from GI disease were from liver disease. GI disease was broken down further into liver disease and non-liver GI disease. Daily, frequent coffee drinking was associated with a decreased risk of dying from liver disease (sexes combined HR, 0.20; 95% confidence interval [CI], 0.13-0.29), cirrhosis (HR, 0.21; 95% CI, 0.13-0.34), and liver cancer, whereas coffee consumption did not decrease the risk of death from non-liver digestive diseases (HR, 0.81) conclusively. Interestingly, in the subcohort, liver function biomarkers (ALP, ALT, AST, and GGT) were significantly lower in people who drank coffee regularly compared with those who rarely or never drank coffee. In women only, higher coffee consumption was associated with lower CRP, HbA1c, lipoprotein (a), and higher high-density lipoprotein. This may account for the decreased risk of dying from heart disease in women who drank more coffee (HR, 0.70; 95% CI, 0.55-0.90). Finally, women who frequently drank coffee were at an increased risk of dying from ovarian cancer (HR, 1.31; 95% CI, 1.07-1.61) when compared to women who did not drink coffee.

MULTIETHNIC COHORT STUDY OF DIET AND CANCER

Until the MEC study, data in non-white populations evaluating coffee consumption and risk for total and cause-specific mortality were sparse. This study included 185,855 African-Americans, Native Hawaiians, Japanese-Americans, Latinos, and whites 45-75 years of age and living in the United States at the time of recruitment. Investigators followed these participants for an average of 16.2 years and assessed coffee intake with a food-frequency questionnaire. Like the EPIC study, the MEC study also featured only two data points: the baseline and the single follow-up. Coffee intake was reported in six categories: none, one to three cups per month, one to six cups per week, one cup per day, two to three cups per day, and more than four cups per day. Drinking coffee decreased the risk of dying across ethnic groups analyzed, even after adjustment for confounding variables: one cup per day (HR, 0.88; 95% CI, 0.85-0.91), two to three cups per day (HR, 0.82; 95% CI, 0.79-0.86), and more than four cups per day (HR, 0.82; 95% CI, 0.78-0.87). Decaffeinated and caffeinated coffee appear to produce similar benefits.

This study was analyzed to control for confounding variables and tease out the specific effect of coffee consumption on mortality. Those in the group of highest consumption of coffee (more than four cups per day) also tended to smoke cigarettes, creating a significant confounding variable in this analysis. Subgroup analyses were conducted for smoking, age, education level, pre-existing heart disease, and pre-existing cancer. A statistically significant inverse association with coffee consumption and mortality was found across these analyses. The association of coffee consumption and mortality was examined across five ethnic groups. An inverse association between coffee consumption and mortality was found with all groups. Statistical significance was reached in all populations except Native Hawaiians.

Total mortality and cause-specific mortality were analyzed in this cohort. After adjustment for confounders, there was a significant inverse association between increasing coffee consumption and all-cause mortality. The HR decreased as coffee consumption increased. The HR for death was 1.00 for one to three cups of coffee per month. In those who consumed one to six cups per week, the HR was 0.97. The lowest HR was 0.82 (95% CI, 0.78-0.87) for two groups: those who consume two to three cups per day and four or more cups of coffee per day. Consumption of both decaffeinated (P trend = 0.008) and caffeinated (P trend < 0.001) coffee decreased the risk of death. This association was similar in both women and men.

To determine if coffee consumption decreased the risk of death from specific causes, the authors analyzed the 10 leading causes of death in the United States. They found a statistically significant inverse association with coffee consumption and cardiovascular disease (P trend < 0.001), cancer (P trend = 0.023), chronic lower respiratory disease (P trend 0.015), stroke (P trend < 0.001), diabetes (P trend = 0.009), and kidney disease (P trend < 0.001). There was no significant association between coffee drinking and death from influenza, pneumonia, Alzheimer’s disease, accidents, and intentional self-harm.

COMMENTARY

Is coffee an elixir of life? These two studies seem to answer with a resounding “yes.” Although the authors generated compelling data and did their best to control for multiple confounding variables, there is not enough cross-cultural data to say definitively that coffee consumption benefits everyone all the time. In each study, only two coffee consumption data points, based on surveys, were generated over nearly 16.5 years. We do not know if coffee was consumed steadily for 16 years, just that it was at the beginning and at the end of the studies. To better assess the frequency and quantity of coffee consumption, multiple data points over several years would strengthen the argument that drinking coffee decreases the risk of death.

In addition, coffee is a popular beverage in many other countries that were not included in the study. According to the International Coffee Organization, the people of Finland consume more coffee per capita than other countries, but this was not included in the European study.2 All the participants in the NEC cohort were from the United States, which ranks 26th in coffee consumption per capita worldwide. Future studies generating data from the countries with higher coffee consumption would provide better data to evaluate the relationship of coffee to mortality more completely.

Previous studies have linked coffee with significant health benefits.3,4 Coffee consumption has been shown to reduce insulin resistance and inflammation, lowering the risk for developing diabetes, metabolic syndrome, heart disease, and cancer. The EPIC researchers found that coffee improved liver function biomarkers and reduced the risk of dying from liver disease.

The health benefits of coffee can be attributed to the many phytochemicals naturally present in coffee.5 These include antioxidants, chlorogenic acid, and caffeic acid. Caffeic acid has been shown to reduce inflammation, induce apoptosis, and produce an anticancer effect. Kahweol and cafestol activate enzymes that alter carcinogens and render them harmless. Coffee also is a source of lignans, compounds that cell culture and animal studies suggest may optimize estrogen metabolism, decrease cancer cell growth, and promote apoptosis of cancer cells.6 The phytochemical content of coffee varies depending on where the beans are grown and how they are prepared for consumption. Laboratory studies show instant coffee may be lower in antioxidants than brewed coffee,7 although more research is needed. Future investigation is needed to learn where the beans richest in these phytochemicals grow and what production methods favor high levels of phytochemicals. In a recent study on healthy adults, drinking up to five cups of coffee per day was not associated with acute toxicity or adverse cardiovascular, behavioral, bone, calcium, or developmental and reproductive effects.8 For now, clinicians can be confident that patients who drink moderate amounts of coffee (up to four cups) daily are not harming themselves and, in fact, likely are benefiting their health and decreasing their risk of death. However, people with a tendency to anxiety, insomnia, and diarrhea need to be careful with coffee, as the stimulant and laxative effect of coffee can exacerbate these conditions.

REFERENCES

  1. Loftfield E, Freedman ND, Dodd KW, et al. Coffee drinking is widespread in the United States, but usual intake varies by key demographic and lifestyle factors. J Nutr 2016;146:1762-1768.
  2. Smith O. Mapped: The countries that drink the most coffee. Available at: https://bit.ly/2pJu6M5. Accessed Aug. 10, 2018.
  3. Crippa A, Discacciati A, Larsson SC, et al. Coffee consumption and mortality from all causes, cardiovascular disease, and cancer: A dose-response meta-analysis. Am J Epidemiol 2014;180:763-775.
  4. Jiang X, Zhang D, Jiang W. Coffee and caffeine intake and incidence of type 2 diabetes mellitus: A meta-analysis of prospective studies. Eur J Nutr 2014;53:25-38.
  5. Patay ÉB, Bencsik T, Papp N. Phytochemical overview and medicinal importance of Coffea species from the past until now. Asian Pac J Trop Med 2016;9:1127-1135.
  6. Webb AL, McCullough ML. Dietary lignans: Potential role in cancer prevention. Nutr Cancer 2005;51:117-131.
  7. Morii H, Kuboyama A, Nakashima T, et al. Effects of instant coffee consumption on oxidative DNA damage, DNA repair, and redox system in mouse liver. J Food Sci 2009;74: H155-161.
  8. Wikoff D, Welsh BT, Henderson R, et al. Systemic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children. Food Chem Toxicol 2017;109:585-648.