There’s lots of interest in this connection because there are studies showing an association between vitamin D blood levels and breast cancer risk: Lower levels show increased risk.
However, Dr. Goodwin pointed out that this association is only observed when blood was drawn after diagnosis. When data was analyzed looking at blood drawn before diagnosis, there was no association. She reported that the strongest studies do not show an association vitamin D and breast cancer risk.
What about for survivors?
For women with diagnosed breast cancer, many studies show low levels of vitamin D status at diagnosis. However, two very recent studies show vitamin D deficiency to be more uncommon, though present in 10-20% of these women. This may be because more women are taking vitamin D supplements.
Some data show an association between vitamin D deficiency and shorter survival, but a randomized clinica trial did not show any association.
With all these conflicting results, what is the take-away message?
Dr. Goodwin’s take:
- The evidence thus far is not convincing that there is a causal association between vitamin D status and breast cancer risk or for prognosis.
- Regardless of the vitamin D and breast cancer association, there are other health problems associated with D deficiency, so it is reasonable to use vitamin D supplementation to obtain sufficient blood levels.
- It will also be important to study, using preclinical studies, what the effects are of higher levels (above sufficient levels) of nutrients, such as vitamin D.
Finally, Dr. Goodwin advises breast cancer patients on chemotherapy to use the standard dose of vitamin D supplement until we know more about chemotherapy and vitamin D.