Vitamin D and Cancer: Why the Question Remains Controversial
Vitamin D has long been investigated for its potential role in cancer prevention and outcomes. Observational studies have consistently linked higher circulating levels of 25-hydroxyvitamin D to lower cancer risk and improved survival. However, observational data cannot establish causality, and randomized controlled trials remain the gold standard for determining whether supplementation itself alters cancer outcomes.
Earlier meta-analyses of randomized trials produced inconsistent findings, in part because most studies used relatively low daily doses of vitamin D and achieved modest increases in circulating 25-hydroxyvitamin D levels. To address these limitations, Keum and colleagues conducted an updated meta-analysis incorporating more recent trials that tested higher supplementation doses and achieved higher blood concentrations.
Study Design: An Updated Meta-Analysis of Randomized Controlled Trials
This meta-analysis pooled data from randomized controlled trials evaluating vitamin D supplementation and its effects on total cancer incidence and total cancer mortality. Trials were identified through systematic searches of PubMed and Embase from inception through November 2018.
