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The public health world is discussing in these days the news that coffee is no longer considered carcinogenic but heat of the drinks is the real culprit.

I'm trying to visualizing this as a causal network, but I'm having some difficulties. If we compare coffe drinkers to not drinkers, heat can or cannot be present only in the drinkers, while it will be always absent in not drinkers. is this a sort of interaction? or is a mediation since heat is provoked by coffe (so to speak). If we compare coffe drinks with other drinks as likely to be hot or not (eg, statistically uncorrelated to heat), heat and coffe are uncorrelated and so a univariate relationship should exist between heat and tumor no relationship for the kind of drink. If we compare coffe with eg. soda, a cold drink, then we have a proper mediation?

I'm clearly confused and would appreciate a more expert opionion.

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  • $\begingroup$ Can you please add a reference to papers/studies showing this? $\endgroup$
    – kjetil b halvorsen ♦
    Commented Oct 16, 2019 at 10:39

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I think I would call this a confounding relationship, not an interaction or mediation. Heat is confounding the apparent causal effect between coffee and cancer. Conditional on heat, coffee has no causal effect on cancer. I would draw the causal diagram as follows:

Coffee <-> Heat -> Cancer

Where <-> indicates correlation (since you can have cold coffee and hot non-coffee beverages), and -> indicates unidirectional causality.

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    $\begingroup$ uhm, I don't agree. A confounder is a phenomenon that cause both exposition and consequence. In this case heat cannot cause coffe exposure. I think it is more correct to interpretate heat as a mediator which convey all relation between coffe and diseases. $\endgroup$
    – Bakaburg
    Commented Jul 25, 2016 at 14:14

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