Breast cancer patients with above-average vitamin D levels had almost a twofold improvement in survival compared with patients who had low levels of the nutrient, authors of a meta-analysis concluded.
Analysis of case-fatality rate across five clinical trials showed that women in the highest quintile of serum 25-hydroxyvitamin D (25[OH]D) had a hazard ratio of 0.56 versus women in the lowest quintile. Results were consistent across the individual studies, as reported in the March issue of Anticancer Research.
"There is no compelling reason to wait for further studies to incorporate vitamin D supplements into standard care regimens since a safe dose of vitamin D needed to achieve high serum levels above 30 nanograms per milliliter has already been established," Cedric Garland, DrPH, of the University of California San Diego said in a statement.
The five studies had a cumulative total of 4,443 breast cancer patients. Garland and colleagues grouped patients into five categories of serum 25(OH)D, the highest being ≥30 ng/mL and the lowest ≤17 ng/mL. The authors noted that 17 ng/mL is the mean 25(OH)D levels among breast cancer patients in the U.S.
Comparison of patients with the highest and lowest values of 25(OH)D showed that women with high levels of vitamin D had a 44% lower risk of death compared with women who had the lowest levels.
The findings add to a previous study by Garland and colleagues, showing that women with a serum 25(OH)D level ≥50 ng/mL had a 50% lower risk of developing breast cancer.
"Vitamin D metabolites increase communication between cells by switching on a protein that blocks aggressive cell division," said Garland. "As long as vitamin D receptors are present, tumor growth is prevented and kept from expanding its blood supply. Vitamin D receptors are not lost until a tumor is very advanced."
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