| Summary: | Current dietary guidelines do not consider cancer survivors’ and past smokers’ low capacity to regulate their acid–base balance. People with a low capacity to regulate their acid–base balance are more susceptible to acid-producing diets. We studied a cohort of 2950 early stage breast cancer survivors who provided dietary information at baseline and during follow-up. We assessed the intakes of acid-producing diets via two commonly used dietary acid load scores: potential renal acid load (PRAL) and net endogenous acid production (NEAP). We assessed past smoking intensity by pack-years of smoking. After an average of 7.3 years of follow-up, there were 295 total deaths, 249 breast cancer-specific deaths, and 490 cases of recurrent breast cancer. Increased intakes of dietary acid load and pack-years of smoking were each independently and jointly associated with increased total mortality and breast cancer-specific mortality; tests for trends and overall associations were statistically significant for NEAP and marginally significant for PRAL. Compared to women in the lowest tertile of NEAP and pack-year of smoking = 0, women in the highest tertile of NEAP and pack-years of smoking >15 had the greatest increased risk of total mortality (HR = 3.23, 95%CI 1.99–5.26). Further, dietary acid scores were associated with increased breast cancer recurrence among women with pack-years of smoking >0 but not in those with pack-years of smoking = 0 (<i>p</i> values for interactions <0.05). Our study provides valuable evidence for adding dietary acid load scores to dietary guidelines for breast cancer survivors and developing specific guidelines for past smokers among these survivors.
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