Association between Vitamin D Intake and Risk of Breast Cancer in Iranian Women: A Case-control Study

Studies suggest a possible protective role of vitamin D against breast cancer. This study aimed to assess the relationship between vitamin D intake and risk of breast cancer in Iranian women. A total of 135 new cases of breast cancer and 135 matched controls were included in the study. The data on breast cancer risk factors، sunlight exposure and use of vitamin D supplements were obtained through demographic questionnaire. To measure the intake of energy، macronutrients، calcium، and vitamin D we used a 168-item semi-quantitative food frequency questionnaire. The mean dietary intake of vitamin D in the cases was significantly lower than the control group (24 vs. 30. 56 IU/day) (P=0. 001). The risk of developing breast cancer was 2. 5 times (61%) lower for those in the highest quartile of dietary intake of vitamin D compared to those in the first quartile (OR=0. 392، 95%CI=0. 196-0. 784). This inverse association was marginally significant in the premenopausal women (OR=0. 39، 95%CI=0. 151-1. 006)، but not in the postmenopausal women. Overall، the total intake of vitamin D from foods and supplements was not associated with breast cancer risk، in both the premenopausal and postmenopausal women. Dietary intake of vitamin D may have a protective role against breast cancer، especially in premenopausal women.