Cedric F. Garland, a professor at the University of California, San Diego School of Medicine, and colleagues performed a statistical analysis of five studies involving 4,443 breast cancer patients on 25-hydroxyvitamin D -- a metabolite, or product of metabolism, produced by the body from the ingestion of vitamin D -- obtained at the time of patient diagnosis and an average nine-year follow up.
"Vitamin D metabolites increased communication between cells by switching on a protein that blocks aggressive cell division," Garland said in a statement. "As long as vitamin D receptors were present tumor growth was prevented and kept from expanding its blood supply. Vitamin D receptors are not lost until a tumor is very advanced. This is the reason for better survival in patients whose vitamin D blood levels are high."
The study, published in Anticancer Research, found women in the high serum group had an average level of 30 nanograms per milliliter of 25-hydroxyvitamin D in their blood, while the low group averaged 17 ng/ml. The average level in patients with breast cancer in the United States is 17 ng/ml, Garland said.
"The study has implications for including vitamin D as an addition to conventional breast cancer therapy," said study co-author Dr. Heather Hofflich, an associate professor at the University of California, San Diego School of Medicine.
Garland recommended randomized controlled clinical trials to confirm the findings but suggested physicians consider adding vitamin D into a breast cancer patient's standard care now and closely monitor the patient.
"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," Garland said.
However, Garland urged patients to ask their healthcare provider to measure their levels of vitamin D before substantially increasing vitamin D intake.