Association of pre-diagnostic vitamin D level with postmenopausal breast cancer risk: A systematic review

Abstract

Introduction: Breast cancer is a disease in which there is a rapid multiplying of cells in the breast. It has been a serious concern as it is the most commonly diagnosed cancer among women, especially in the old-age group. Vitamin D is a fat-soluble vitamin that is consumed via diet or produced when the ultraviolet (UV) rays of the sun make contact with the skin. Its putative anticarcinogenic property might play a role to minimize the increasing burden of breast cancer. Thus, this study focuses on vitamin D level as a risk factor for postmenopausal breast cancer.

Methodology: A systematic review of prospective cohort studies was conducted. The search was performed in MEDLINE (Ovid) using the mesh terms and keywords of the modified PICOS diagram. The free-text search was done in Google Scholar. The reference lists of relevant systematic reviews were screened manually. The population for the review was healthy women, the exposure was vitamin D level, and the outcome was postmenopausal breast cancer. The information from the eligible studies was extracted and presented in the table. The Risk of bias (RoB) assessment was done using a CASP tool.

Results: Eight studies met the inclusion criteria. All the studies were prospective cohorts. The included studies were conducted in high-resource settings. The study population was diverse. Vitamin D was measured in various forms and the data was collected using a questionnaire. Breast cancer occurrence was self-reported but was confirmed through reports. The effect estimates of the fully adjusted models in the included studies ranged from 0.87 to 1.30. The result showed that there was no association between pre-diagnostic vitamin D level and postmenopausal breast cancer risk.

Conclusion: The review does not have enough evidence to conclude the association between pre-diagnostic vitamin D level and postmenopausal breast cancer risk. Further research is necessary to assess the relationship.