Vitamin D Status and Cancer Incidence, Survival, and Mortality

Over the last several decades, extensive research on vitamin D and its role on cancer incidence, cancer survival (survival or mortality from cancer among individuals diagnosed with cancer), and cancer mortality (fatal cases occurring during the study period in an initially cancer-free population) has been conducted. A variety of study designs were implemented to explore vitamin D status, assessed by measuring sun exposure, vitamin D intake, and circulating 25-hydroxyvitamin D (25(OH)D) concentration. Although not many randomized controlled trials have examined the relationship between vitamin D and cancer incidence, observational studies have consistently shown a protective association between vitamin D and cancer incidence, especially for colorectal cancer. In addition, randomized controlled trials and most observational studies suggested that vitamin D plays a role in reducing cancer mortality. The potential benefit of vitamin D on cancer mortality may operate during the pre-diagnostic stages by affecting late-stage tumor progression and metastatic seeding, during the treatment phase by complementing or enhancing effects of therapies, or during the post-diagnostic stages. However, further studies are needed to confirm these conclusions, establish the optimal dosage and timing of vitamin D intakes for the most benefit, find which cancer types are affected, and understand the underlying mechanisms.