The Association between Vitamin D Status and Risk of Breast Cancer in Iranian women

Background: Increase in the incidence of breast cancer during the 4 past decades has made it the most prevalent cancer among the Iranian women. Some of current evidence support the association between vitamin D status and breast cancer development. Although the role of vitamin D in breast cancer incidence and outcomes is controversial. Results from some studies support the inverse association between vitamin D intake or serum concentration and risk of breast cancer. Therefore, considering the conflicting results of previous studies and high prevalence and rising incidence of breast cancer and high prevalence of vitamin D deficiency in Iran, this case-control study aimed to investigate the relationship between intake and serum concentration of vitamin D and risk of breast cancer. Methods and Materials: A total of 135 incident breast cancer cases in the Cancer Research Center of Shahid Beheshti University of medical sciences were matched with 135 controls by age and menopausal status. Information on the risk factors of breast cancer was collected to assess the role of confounding factors in the relationship between vitamin D and breast cancer. A 168-item food frequency questionnaire was filled by interviews for every participants to assess dietary intake of vitamin D and some other dietary factors. To determine the vitamin D content of foods we used the USDA nutrient database. For analyzing the food frequency questionnaires we used the food composition table for the comprehensive plan for assessment of nutrient intakes in 1381-83. 5 mL blood samples were collected from all participants to measure serum 25(OH) D using ELISA method. Results: Dietary intake of vitamin D was inversely associated with risk of breast cancer so that the odds ration of the forth quartile of dietary vitamin D intake compared to the first was 0.392 (P=0.008). After adjusting for the confounding factors this inverse association remained ignificant and the risk of developing breast cancer for those in the Forth quartile was 2.6 times lower compared to those in the first quartile. When the participants were stratified by menopausal status the inverse association remained marginnaly significant in premenopausal women but not in postmenopausal participants. Women who were in the Forth quartile of serum 25(OH) D level had 3 times lower risk of developing breast cancer compared to women in the first quartile. In adjusted model the inverse relationship between serum 25(OH) D concentration and risk of breastcancer remained significant OR (95% CI) = 0.269(0.122-0.593). In the stratified model the inverse association was only seen in premenopausal women OR (95% CI) = 0.25(0.094-0.687). Conclusion: Results from this case-control study support the protective effect of higher serum concentration of 25(OH) D against breast cancer. Moreover, dietary but not total intake of vitamin D was associated with decreased risk of breast cancer.

Keywords:

Breast cancer , Vitamin D , Intake , 25(OH) D