A growing body of laboratory and animal evidence as well as epidemiological data shows low levels of vitamin D may contribute to certain types of cancer. Conversely, strong biological and mechanistic bases indicate that vitamin D may play some role in the prevention of colon, prostate, and breast cancers.
Vitamin D is essential for promoting calcium absorption for bone and overall health in people. Low levels of vitamin D can lead to rickets in infants and children and the loss of bone density in adults.
More than 25 million adults in the United States have or are at risk of developing osteoporosis, a disease characterized by the loss of bone density that makes bones fragile and significantly increases the risk of fractures. When it comes to Osteoporosis, it’s a chicken and egg scenario: osteoporosis is most often associated with inadequate calcium intakes (generally less than 1,000-1,200 mg/day), but insufficient vitamin D contributes to osteoporosis by reducing the body’s calcium absorption.
While the evidence is far from conclusive, vitamin D may also prove to be an important protective nutrient in the prevention and treatment of cancer.
In a 2008 study, University of Toronto researcher, Pamela Goodwin, MD, and colleagues measured vitamin D levels in the blood of 512 newly diagnosed breast cancer patients (95% of them Caucasian) and tracked the progress of their disease over an average of about 12 years. Women in the study with the lowest levels of vitamin D (deficient) had nearly double the risk of their breast cancer progressing, and had a 73% greater risk of death compared to women with adequate vitamin D levels. The findings were statistically significant, and were not affected by other factors including age, weight, tumor stage, or tumor grade.
The University of Toronto study found about 38% of the women in the study had vitamin D levels low enough to be considered "deficient" and 39% had levels that were "insufficient." Just 24% of the women in the study had "adequate" vitamin D levels.