Pre- and post-diagnostic intake of whole grain and dairy products and breast cancer prognosis: the Danish Diet, Cancer and Health cohort

Purpose Fiber rich foods and dairy products have been suggested to be associated with breast cancer prognosis, though existing research is limited and either report on pre- or post-diagnostic dietary intake in relation to breast cancer prognosis. We investigated the associations between intake of whole grain (WG) and dairy products assessed both pre- and post-diagnostically in relation to breast cancer prognosis. Methods A total of 1965 women from the Diet, Cancer and Health cohort who were diagnosed with breast cancer between baseline (1993-1997) and December 2013 were included and followed for a median of 7 years after diagnosis. During follow-up, 309 women experienced breast cancer recurrence and 460 women died, of whom 301 died from breast cancer. Dietary assessment by food frequency questionnaires was obtained up to three times, pre- and post-diagnostic, over a period of 18 years. Cox proportional hazard models were used to estimate hazard ratios. Results No associations were observed between pre- or post-diagnostic intake of total WG or total dairy products and breast cancer prognosis. A high pre-diagnostic intake of oatmeal/muesli was associated with lower all-cause mortality (HR 0.76, 95% CI 0.59-0.99), whereas high post-diagnostic intake of rye bread was associated with higher breast cancer-specific mortality (HR 1.29, 95% CI 1.02-1.63). A generally high intake of cheese was associated with a higher recurrence rate. Conclusion Pre-diagnostic intake of oatmeal/muesli was associated with lower all-cause mortality, and post-diagnostic intake of rye bread was associated with higher breast cancer specific mortality.