We looked at instant coffee, we looked at filtered coffee, and espresso-type coffee and found that all brewing methods had a protective effect. In other words, the method of coffee brewing made no difference. However, decaffeinated coffee showed no association with risk, so that people that were drinking decaffeinated coffee were not at a decreased risk. We believe that caffeine is probably the protective agent because caffeine is the main constituent in coffee. But we cannot rule out that other components in coffee may have also contributed to the benefit.
Many people prefer a cup of tea.
We looked at the consumption of tea and we also looked at the consumption of other caffeinated beverages, soft drinks, and found that they were not protective, which means either that they do not have enough caffeine, or they lack the other components that appear to be present in coffee. We took into account other variables such as age, obesity, intake of dietary fat and physical activity. So we needed to adjust for the variables I just mentioned, in order to make sure that we were looking at the relationship between coffee and gallstone disease and we were not looking at the relationship that would be confounded by other variables that are also related to both coffee drinking and gallstone disease. Most gallstones produce no symptoms at all, and you may never even notice they're there. In our study we looked at only symptomatic gallstones, those gallstones that were creating symptoms, and so we did not address the association between coffee consumption and non-symptomatic gallstone disease.