I assume this would fall into the confounding part: culturally we see coffee as a drug that can have adverse effects, and will make efforts to limit its consump

I assume this would fall into the confounding part: culturally we see coffee as a drug that can have adverse effects, and will make efforts to limit its consumption when health deteriorates. For instance, I would expect people to not drink coffee if they have chronic stomach illness or are under a pretty strict diet, or heavily medicated. This could heavily skew results of how long heavy coffee drinkers tend to live.