The Coffee Debate

Does your morning cup of joe do your body good? 

Some studies have said yes, suggesting a modest benefit of coffee on overall mortality. Coffee’s high caffeine content, though, and its potential as a vehicle for extra sugar and fat may pose certain health risks. Then there’s the question of decaffeinated coffee. Does coffee without its kick have the same effect on health?

A new study has added fuel to the debate. The study looked at the associations between coffee drinking and the ten leading causes of death in the US. Results showed that coffee drinkers had up to 21% decreased risk in overall mortality, and that they had lower risk of death from common diseases like heart disease and diabetes. Results were similar for decaffeinated coffee drinkers, and for those who used coffee additives like milk, cream and sugar.

The study was published online in the American Journal of Epidemiology. 

“Coffee drinking was inversely associated with overall mortality in this large, population-based cohort following adjustment for smoking history and other potential confounders,” wrote first author Erikka Loftfield, MPH, of the Nutritional Epidemiology Branch at the National Cancer Institute, Rockville, MD, and colleagues.

“This association was largely due to inverse associations with several leading causes of death, including heart disease, chronic lower respiratory diseases, diabetes, influenza and pneumonia, and intentional self-harm,” they added.

Participants in the study came from the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial, a large population-based cohort study of 90,317 US adults from ten centers across the US. Researchers used questionnaires to obtain self-reported information on diet and coffee consumption from participants. They also used questionnaires along with the National Death Index to identify the cause of death.

Results were adjusted for smoking, family history of cancer, lifestyle and dietary factors potentially associated with death, and other potential confounders. To address the question of whether participants in poor health may have decreased their coffee intake, researchers adjusted results for employment status and excluded participants with a history of cancer, coronary heart disease, heart attack, stroke, hypertension, and gastrointestinal disorders.

During the study (1998-2009), 8718 deaths occurred. 

Key results showed that coffee drinking was linked to lower mortality:

• Overall mortality (P for trend <0.001):

♦ <1 cup/day: hazard ratio (HR)=0.99 (95% confidence interval (CI): 0.92, 1.07)

♦ 1 cup/day: HR=0.94 (95% CI: 0.87, 1.02)

♦ 2–3 cups/day: HR=0.82 (95% CI: 0.77, 0.88)

♦ 4–5 cups/ day: HR=0.79  (95%CI: 0.72, 0.86)

♦ ≥6 cups/day: HR=0.84 (95%CI: 0.75, 0.95)

♦ Similar results for coffee additives (cream and sugar) and decaffeinated coffee, but the latter were not statistically significant

• Heart disease: HR 0.75 (0.63, 0.90)

• Chronic lower respiratory diseases: HR 0.68 (0.48, 0.97)

• Diabetes: HR 0.88 (0.48, 1.60)

• Intentional self-harm: HR 0.50 (0.18, 1.42)

Results did not show a relationship between coffee drinking and cancer death. The authors noted, though, that the study may not have been long enough to capture cancers that take a long time to develop, like prostate cancer. Additionally, only 23% of participants drank only decaffeinated coffee, and the study may have been underpowered to detect statistically significant differences for this group.

Drinking coffee may lower the risk of death by decreasing inflammation and improving lung function, insulin sensitivity, and depression, the authors conjectured. Past studies have linked coffee drinking to better insulin sensitivity, lower risk for type 2 diabetes, and lower levels of inflammatory markers. The coffee metabolite theophylline, which is used to treat lung disease, and biologically active compounds in coffee, like phenols, potassium, and caffeine, may play a role. But that remains an open question.

 “Additional experimental and observational studies are needed to better understand the potential mechanisms underlying the observed associations,” they concluded, “Although our results may provide reassurance to coffee drinkers, they are based on observational data and should be interpreted with caution.”

Take-home Points

• Observational cohort study found that drinking coffee is linked to up to 21% decreased risk of overall mortality.

• Drinking coffee was also linked to lower risk of heart disease, diabetes, chronic lower respiratory diseases, and intentional self-harm.

• Similar results were found for decaffeinated coffee drinkers and additives like cream and sugar

• More studies are needed to confirm these findings and evaluate underlying mechanisms.

Reference: Loftfield E, et al. Association of coffee consumption with overall and cause-specific mortality in a large US prospective cohort study. Am J Epidemiol. Epub ahead of print 27 Nov 2015.