To the Editor While the European Prospective Investigation into Cancer and Nutrition database that Mullee and colleagues1 used to assess the association between soft drink consumption and mortality is quite detailed on treatment exposure (in this case, soft drink servings), such detail is lacking for many potentially important explanatory variables. In nonrandomized (real-world) data, treatment selection can be biased by unobservable confounders or inadequately measured explanatory variables, including in this case: drug use additional to alcohol, detailed exercise and physical activity tracking, income, wealth, education, race/ethnicity, mental health, comorbidities, family and friends, job stress, sleep, major life events, etc. If the association between soft drinks and mortality is not causal, but due to unobserved lifestyle or other factors, then intervening on soft drink consumption directly (eg, through soda taxes or serving size/quantity reductions) will not get at the root cause of the problem.
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Hay JW, Zawadzki NK, Zawadzki R. Hypertension and Unlikely Causality in the Association Between Soft Drink Consumption and Mortality. JAMA Intern Med. 2020;180(2):335–336. doi:10.1001/jamainternmed.2019.6105
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