This is the first study that derived a dietary pattern specifically correlated with estrogen levels. The dietary pattern derived with this method had modest association with estradiol and estrone sulfate but was not associated with post-menopausal breast cancer. Data on the association between dietary patterns and estrogen levels are scarce. In this cohort, a higher Alternate Healthy Eating Index (AHEI) was associated with lower concentrations of estradiol [5
] and in a small 6-month intervention study, the Mediterranean diet resulted in lower levels of estradiol without any appreciable difference in weight change compared with the typical diet group [3
]. Although the AHEI was associated with a lower risk of ER- breast cancer [21
], this subtype is unlikely to be strongly influenced by estrogen levels. Therefore, although lower estrogen was observed with higher AHEI score, the components of AHEI likely influenced breast cancer risk through other mechanisms.
RRR overcomes the weak association between single foods and biomarker levels by being able to derive a dietary pattern that is correlated with multiple biomarkers. Although the RRR procedure has been applied to breast cancer in two studies, results were mixed and the response variables were dietary factors [11
]. A dietary pattern associated with fatty acid intake, characterized by low intake of bread, fruit juices, but high intake of processed meat, fish, and fats was associated with fatty acids intake, was associated with higher risk of breast cancer [12
]. On the other hand, a diet correlated with glycemic load, characterized by higher intakes of sweets, refined grains, and salty snacks, had no association with breast cancer [11
]. The strength of association between RRR patterns and breast cancer depends on the correlation between the RRR patterns and biomarkers, as well as the strength of association between biomarkers and breast cancer. Although we observed a significant association between the dietary pattern and estrogens, the correlation may be was insufficiently strong to have represented a change in a magnitude that would influence breast cancer risk.
This study included a substantial sample to identify food groups correlated with estrogen, and a large number of cases to separately examine ER+ and ER− tumors. We had detailed information on potential confounders but since lifestyle factors were self-reported, some level of measurement error was inevitable. The sample size for the estrogens was substantial, but that does not guarantee that the distribution would sufficiently reflect the distribution of these biomarkers in the main cohort.
In conclusion, although a diet pattern characterized by higher intakes of red meat, legumes, and pizza, but lower intakes of coffee and whole grains was modestly associated with estradiol and ES, it was not associated with postmenopausal breast cancer risk. Although we did not identify a dietary pattern with strong association with estrogens, other populations may consume different foods in different amounts that may find otherwise. Therefore, the association between food groups and estrogen levels and their relationship with breast cancer should be explored in other populations.