Researchers at University of California, San Diego School of Medicine looked at the results of two previous studies—a randomized clinical trial of 1,169 women, and a prospective study of 1,135 women—to determine what blood level of vitamin D (specifically serum 25-hydroxyvitamin D or 25(OH)D, the main form in blood) was necessary to reduce the incidence in overall cancer risk.
The clinical trial looked at the safety and efficacy of vitamin D supplementation, while the prospective study observed the incidence of cancer among subjects.
The researchers found that in the clinical trial, the median blood level of 25(OH)D was 30 nanograms per milliliter (ng/mL,) while in the prospective study it was 48ng/mL. The cancer incidence (adjusted for age) was 1,020 cases per 100,000 person-years in the clinical trial, and 722 cases per 100,000 person-years in the prospective cohort.
The incidence of cancer declined when subjects had higher levels of vitamin D. Women with vitamin D levels of 40ng/mL or more had a 67 percent lower risk of cancer than women who had vitamin D levels of 20ng/mL or less.
In 2010, the Institute of Medicine (IOM) recommended a vitamin D blood level target of 20ng/mL, while other medical experts have argued that significantly higher levels (up to 50ng/mL) are more desirable.
“These findings support an inverse association between 25(OH)D and risk of cancer, and highlight the importance for cancer prevention of achieving a vitamin D blood serum concentration above 20ng/mL, the concentration recommended by the IOM for bone health,” said Cedric Garland, DrPH, one of the study authors and adjunct professor in the UC San Diego School of Medicine Department of Family Medicine and Public Health.
“Primary prevention of cancer, rather than expanding early detection or improving treatment, will be essential to reversing the current upward trend of cancer incidence worldwide,” the study authors wrote. “This analysis suggests that improving vitamin D status is a key prevention tool.”
The study was published in PLOS ONE, a scientific journal published by the Public Library of Science.
