Relationship between diet diversity score and breast cancer risk

Background: The average age of women with breast cancer in Iran is at least 10 years lower in comparison to developed countries and the incidence of the disease in Iranian women is on a rise. According to studies, diets that are diverse in food groups can play a role in protecting against chronic diseases including cardiovascular diseases and cancer. Diet diversity score is an indicator used to measure diversity between and within food groups. This study aimed to assess the relationship between diet diversity score and breast cancer risk. Methods: This case-control study was carried out from April 2014 to February 2015 at Shohada Hospital in Tajrish, Tehran. Demographic and anthropometric data of 298 participants including 149 breast cancer cases and 149 apparently healthy women were collected. A valid food frequency questionnaire containing 168 food items was completed to assess usual dietary intake through face to face interviews. Energy was calculated using Nutritionist 4 software (First Databank Inc., Hearst Corp., San Bruno, CA, USA) and diet diversity score was calculated using five food group scoring. Odds ratios with 95% confidence intervals were obtained using logistic regression test to evaluate the association between breast cancer risk and diet diversity score tertiles. Results: There was no significant difference in weight, height, body mass index between the two groups, but physical activity level and daily energy intake showed a significant difference (P<0.001). After adjusting for the effect of confounding variables including energy, body mass index, physical activity, menopause status, family history of breast cancer, contraceptive use, number of pregnancy, age of menarche and smoking, the risk for developing breast cancer was 86% lower in those in the highest tertile of diet diversity score compared to those in the first tertile (OR=0.14, 95% CI=0.06-0.31). An inverse and significant association was found between breast cancer risk and diversity scores of fruits and milk groups (P<0.001). Conclusion: Higher diet diversity score is associated with reduced risk of breast cancer.