Women who more closely followed a diabetes risk-reduction diet both before and after a diagnosis of breast cancer had lower risks for breast cancer–specific and all-cause mortality when compared with women with less healthy diets or those who did not substantially modify what they ate following diagnosis, according to pooled data from two prospective cohort studies.
Among more than 8,000 participants in the Nurses’ Health Study and NHS II, those who most closely adhered to a dietary pattern associated with lower risk for type 2 diabetes had a 13% lower risk for breast cancer–specific mortality and a 31% lower risk for death from any cause, compared with those at the bottom of the diabetes risk-reduction diet chart, reported Tengteng Wang, PhD, of the Harvard School of Public Health, Boston, and colleagues.
“Promoting dietary changes consistent with prevention of type 2 diabetes may be very important for breast cancer survivors,” Dr. Wang said in an oral abstract presentation at the 2020 San Antonio Breast Cancer Symposium.
Poor outcomes
Type 2 diabetes has been shown to be associated with poor outcomes for women with breast cancer, prompting the investigators to see whether diet modification could play a role in improving prognosis.
They looked at self-reported dietary data from 8,320 women diagnosed with stage I-III breast cancer who were participants in NHS, with data from 1980 to 2014, and NHS II, with data from 1991 to 2015.
Every 2-4 years, participants filled out validated follow-up questionnaires, including information on diet.
The investigators calculated a diabetes risk-reduction diet (DRRD) adherence score based on nine components, including higher intakes of cereal fiber, coffee, nuts, and whole fruits, as well as a higher polyunsatured to saturated fat ratio, and lower glycemic index, plus lower intakes of trans fats, sugar-sweetened beverages and/or fruit juices, and red meat.
The investigators calculated cumulative average DRRD scores based on repeated measures of diet after breast cancer diagnosis. They obtained data on deaths from family reports or the National Death Index, and they determined causes of death from either death certificates or medical records.
At a median follow-up of 13 years, 2,146 participants had died, with 948 of the deaths attributed to breast cancer.
After adjusting for socioeconomic factors, postdiagnosis time-varying covariates, and key breast cancer clinical factors, there was a nonsignificant trend toward a lower risk for breast cancer–specific deaths in the women in the highest versus lowest quintiles of DRRD score (hazard ratio, 0.87; P = .13), but significantly lower risk for all-cause mortality risk (HR, 0.69; P < .0001).
Looking at participants who changed their diet following breast cancer diagnosis, those who went from a low DRRD score prediagnosis to a high score post diagnosis had a 20% reduction in risk for breast cancer–specific mortality and a 14% reduction in risk for all-cause mortality, the investigators found (P values for this analysis were not shown).
There were no differences in results by either tumor estrogen receptor status or stage.
Dr. Wang acknowledged that the study was limited by the population (which was predominantly composed of educated, non-Hispanic White women), errors in dietary measurement, and limited power for estrogen receptor–negative tumor analysis.