Smoking and caffeine use are correlated primarily due to genetics, not environment or causality. The largest ever twin study of its kind combined with GWAS data and a separate longitudinal twin study indicates that genetic factors may make quitting smoking more difficult for heavy caffeine drinkers.

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Smoking and caffeine use are correlated primarily due to genetics, not environment or causality. The largest ever twin study of its kind combined with GWAS data and a separate longitudinal twin study indicates that genetic factors may make quitting smoking more difficult for heavy caffeine drinkers.