The relationship between vitamin D levels and cancer risk is a complex one, but a growing body of evidence points to a strong correlation between vitamin D deficiency and increased odds of many types of cancer.
A new prospective study of 512 women with early-stage breast cancer suggests that those with the low serum vitamin D levels were more likely to die of their cancers than those with sufficient D levels.
The women were all diagnosed with breast cancer between the years 1989 and 1996, and had a mean age of 50 years at the time of diagnosis. Average vitamin D levels in blood samples stored at time of diagnosis was 58.1 nmol/L.
The researchers, led by Pamela J. Goodwin, MD, of the Division of Clinical Epidemiology, Mount Sinai Hospital, Toronto, classified vitamin D levels as “deficient” (<50 nmol/L) in 192 of the patients (37.5%), “insufficient” (50-72 nmol/L) in 197 (38.5%) and “sufficient” (> 72 nmol/L) in 123 women (24%).
During an average follow-up period of 11.6 years, 116 of the women had distant recurrences and 106 women died from breast cancer. Vitamin D levels at diagnosis turned out to be significantly predictive of both bad outcomes.
Those women with vitamin D deficiency had an increased risk of distant recurrence (hazard ratio of 1.94) and of death (HR of 1.73), compared with those women who had sufficient serum vitamin D levels (Goodwin P, et al. J Clinical Oncology 2009;27(23): 3757-3763.)
The elevated hazard ratios remained after adjustment for a host of tumor and treatment related variables, leading the authors to conclude that, “Vitamin D deficiency may be associated with poor outcomes in breast cancer.”
They note that this is scientifically plausible given vitamin D’s role as a nuclear transcription factor and regulator of gene activity, and the fact that vitamin D receptors have been identified in breast cancer cells.
This is not the first time that associations have been reported between low vitamin D and breast cancer. In terms of using vitamin D levels to determine the initial risk for breast cancer, the evidence has been mixed, with some studies showing an association between latitude and risk of breast cancer, and others showing an inverse relationship between vitamin D intake and breast density (a strong risk factor for breast cancer). However, other studies show no consistent relationship between vitamin D intake or blood levels of vitamin D and actual incidence of breast cancer.
There have been other attempts to use vitamin D levels as a prognostic indicator for breast cancer and mortality. Low vitamin D levels have been associated with increased breast cancer mortality, and there are data showing significantly lower vitamin D levels in women with locally advanced or metastatic disease compared with those women who have early-stage breast cancers.
In light of the current study, I would definitely recommend testing vitamin D levels in all current or past breast cancer patients, and supplementing when appropriate.
Taking a vitamin D supplement to increase blood levels is one of the least expensive, and safest options we have for potentially reducing risk of recurrence of breast cancer recurrence and/or death.
For all women, higher blood levels of vitamin D are associated with lower rates of heart disease, ovarian cancer, multiple sclerosis, osteoarthritis, rheumatoid arthritis, and bacterial vaginosis. So there are a lot of reasons to pay attention to vitamin D levels, and many collateral benefits to optimizing serum vitamin D in women with breast cancer.
It should be noted that Dr. Goodwin’s current study, and in fact many studies, report vitamin D levels in the units of nmol/L. Others report in ng/ml. This is a very important difference. When testing patients and trying to correlate their levels with the risk profiles described in the literature, it’s important that you use consistent units, and make the proper mathematical conversions if necessary.
For reference, 75 nmol/L is equal to 30 ng/mL. In the current study, vitamin D deficiency as defined by < 50 nmol/L would be equivalent to < 20 ng/ml, using a nanogram reporting scheme.