Increasing vitamin D levels may lower risk for developing cancer, according to a study conducted by Creighton University with cooperation from the University of California San Diego. The results of the study were released today in the Journal of the American Medical Association. The study, funded by the National Institutes of Health, is a randomized clinical trial of the effects of vitamin D supplementation on all types of cancer combined.
The four-year study included 2,303 healthy postmenopausal women 55 years and older from 31 counties in Nebraska. Participants were randomly assigned to take either 2000 international units (IU) of vitamin D3 and 1500 mg. of calcium or identical placebos daily for 4 years. The vitamin D3 dose was about three times the US government's Recommended Dietary Allowance (RDA) of 600 IU for adults through age 70, and 800 IU for those 71 and older.
Women who were given vitamin D3 and calcium supplements had 30% lower risk of cancer. This difference in cancer incidence rates between groups did not quite reach statistical significance. However, in further analyses, blood levels of vitamin D, specifically 25-hydroxyvitamin D (25(OH)D), were significantly lower in women who developed cancer during the study than in those who remained healthy.
The average 25(OH)D level in the women's blood at the beginning of the study (33 nanograms/milliliter, ng/mL) was higher than the usual target levels that currently range from 20-32 ng/ml, according to different sources. This suggests that higher vitamin D levels than are currently recommended are needed for substantially decreasing risk of cancer.
Scientists at the Spanish National Cancer Research Centre examined more than 2,000 respondents and observed higher bladder cancer risk in patients with significantly low vitamin D levels. Vitamin D deficiency appeared to worsen the risk for patients with muscle-invasive tumors. However, increased vitamin D levels mitigated the risk of bladder cancer progression in patients with non-muscle invasive bladder cancer, researchers said. The results were published in the Journal of the National Cancer Institute.
Another study published in the journal PLOS One revealed that higher vitamin D levels mitigate the risk of cancer. Researchers at the University of California-San Diego found that women with vitamin D levels at 40 ng/ml or higher had a 67% lower risk of developing cancer than those whose vitamin D levels were at 20 ng/ml or lower.