There's a tremendous amount of research available on the benefits of drinking coffee. Much of that research has attributed its positive health effects on the large amounts of antioxidants it contains, whether that's caffeinated or decaffeinated.
While there are some cases when you might want to switch to decaf (like those with an enlarged prostate), caffeinated coffee may help prevent high blood pressure and improve markers of inflammation in those with diabetes.
One of the difficulties in measuring the effects of any specific substance on health is in knowing for sure how much of that substance has actually been consumed by a study participant. Questionnaires are helpful, as are food diaries, but the gold standard is measuring the substance's byproducts (its metabolites) that appear in an individual's blood or urine after consumption.
A team at the National Institute of Health sought to identify some of coffee's metabolites, and along the way investigate what, if any, links they might find between those metabolites and colon cancer. Previous research into a possible link between coffee intake and colon cancer were inconclusive, but coffee is prepared in so many different ways that it is difficult to standardize intake: how do you compare drip coffee with espresso or eating chocolate-covered coffee beans with lattes? Identifying coffee's metabolites would help later research with that problem.
A long-term screening trial of prostate, lung, and colorectal cancers, known as The PLCO Cancer Screening Trial, provided the data for the team's analysis. Those 498 male and female participants who completed a risk-factor questionnaire, a detailed dietary questionnaire, and provided blood samples were included in their case-control study. (Recall that a case-control study matches individuals with a certain condition to similar individuals without that condition and compares the differences between the two groups in order to highlight possible risk factors for that condition.)
The researchers were able to identify coffee metabolites by using mass spectrometry and gas chromatography: To put it very simply, they found 29 metabolites, including 7 they had never seen before, that appeared in larger numbers in those who reported higher coffee intake, leading the team to conclude that those metabolites were indeed coffee metabolites.
When they compared the levels of those known and unknown coffee metabolites in those who developed colorectal cancers with those who did not, they found that 2 substances, theophylline and caffeine, were associated with a 25% and 19% reduction, respectively, in the risk of colorectal cancers as compared to those with the lowest levels of those metabolites. Two previously unknown metabolites were linked to 15% and 17% reduction in risk.
Three of the 4 metabolites linked to a lower risk of colorectal cancer appear in both caffeinated and decaffeinated coffee; obviously caffeine only appears in caffeinated coffee.
Source: GP Clinics Vol 7 No 10, January 2017