by Avis Antel

Vitamin D, primarily produced by synthesis when ultraviolet rays from the sun strike the skin, has long been considered (along with calcium) important to maintenance of healthy bone. Now recent research seems to indicate that low levels of vitamin D could be a factor in a range of other ailments, including cardiovascular disease, diabetes, multiple sclerosis, and the flu, as well as colorectal, prostate, and breast cancers.

The Canadian Cancer Society is recommending that we consume 1,000 IU of vitamin D daily, an amount much higher than suggested by Health Canada. During spring and summer, normal daily sun exposure may be sufficient but, during fall and winter, a vitamin D supplement may be necessary, especially in climates like ours.
A study published in the Archives of Internal Medicine (2007 May 28; 167(10): 1050-9) suggests that women who consume higher amounts of calcium and vitamin D may have a lower risk of developing breast cancer before, but not after menopause. According to this study, the lower risk was more pronounced in relation to aggressive breast tumours, which tend to be diagnosed more often in younger women. Calcium and vitamin D may work with insulin-like growth factors (IGfs) to discourage the growth of breast cancer cells.

In a 2008 Canadian study¹, researchers were interested in looking at vitamin D because breast cancer cells have receptors able to use it. These receptors influence an estimated 30 to 40 genes that, among other functions, play a role in cell reproduction, a crucial factor in the out-of-control growth characterized by cancer. Although this research indicates that lower levels of vitamin D status raise the risk of death from breast cancer, conclusive proof that vitamin D levels play a part in cancer progression and death would require a drug-style trial. Ascertaining an optimum amount of vitamin D supplementation would also require further research.

In sum, while no direct cause-and-effect relationship has been established between vitamin D levels and breast cancer, and the optimal amount of vitamin D is still unknown, current thinking and research support the recommendation that we should all pay attention to sunshine and vitamin D.

1 Goodwin, P et al. Frequency of vitamin D deficiency at breast cancer diagnosis and association with risk of distant recurrence and death in a prospective cohort study of T1-3, N0-1, M0 BC. Presented at the 2008 annual meeting of the American Society of Clinical Oncology.