Association between dietary phytochemical index and breast cancer: a case-control study

Dietary intake of isoflavones has been positively associated with risk of breast cancer (BC) in some earlier studies. In addition, most studies on diet-disease associations came from western countries and limited data are available in the Middle-East.

This case-control study was performed on 350 women with BC aged over 30 years who were recruited from hospitals or private clinics in Isfahan, Iran. All patients were diagnosed with BC during the maximum of the last 6 months using physical examination and mammography findings. Using cluster method sampling, 700 apparently healthy age- and socioeconomic status-matched controls were randomly selected from healthy women who had no relationship with BC patients and had no familial history of BC. Data on dietary intakes were collected using a validated food-frequency questionnaire. The DPI was calculated based on dietary energy derived from foods rich in phytochemicals (kcal) divided by total daily energy intake (kcal) of each participant.

Mean ± SD age and BMI in the study participants were 62.4 ± 10.8 years and 24.3 ± 5.2 kg/m², respectively. In the crude model, participants in the highest quartile of DPI had 63% lower odds of breast cancer compared to those in the lowest quartile (95% CI 0.26, 0.54; P-trend < 0.001). After adjustment for potential confounders, this inverse association became strengthened (95% CI 0.22, 0.49; P-trend < 0.001). Further adjustment for BMI did not change the association (OR for the highest quartile vs. the lowest quartile = 0.40, 95% CI 0.26, 0.60; P-trend < 0.001).

In conclusion, a protective association was observed between DPI and BC in this case-control study. Therefore, high consumption of foods rich in phytochemicals such as fruits, vegetables, and whole grains might help reducing the odds of BC among women.