Vitamin D's Impact on Cancer Incidence and Mortality: A Systematic Review

Area of Science:

• Nutritional Science
• Oncology
• Preventive Medicine

Background:

• Vitamin D is vital for numerous physiological processes, including immune function and DNA repair.
• Widespread vitamin D deficiency persists due to insufficient intake and limited sun exposure.
• Vitamin D supplementation is a cost-effective strategy for maintaining adequate levels.

Purpose of the Study:

• To systematically review the evidence on vitamin D's role in cancer risk and mortality reduction.
• To explore the mechanisms by which vitamin D may prevent cancer.
• To evaluate the quality of evidence from observational studies and randomized controlled trials.

Main Methods:

• Systematic review adhering to PRISMA and PICOS guidelines.
• Synthesis of evidence from diverse studies investigating vitamin D and cancer.
• Analysis of both genomic and non-genomic mechanisms of vitamin D action.

Main Results:

• A significant inverse relationship exists between serum 25-hydroxyvitamin D levels and the incidence, metastasis, and mortality of numerous cancer types.
• Optimal serum 25-hydroxyvitamin D levels for cancer prevention are above 40 ng/mL (100 nmol/L).
• Vitamin D exerts protective effects through anti-inflammatory and signaling pathways, beyond its genomic actions.

Conclusions:

• Observational studies strongly support vitamin D's protective role against cancer.
• Recent large randomized controlled trials showing no benefit are flawed due to study design issues.
• Well-designed trials confirm that adequate vitamin D supplementation effectively reduces cancer risk and mortality.