Laura N. Anderson, one of the study’s authors, at Cancer Care Ontario in Toronto undertook a fairly large scale (6,500+ patients) study on vitamin D which has shown that even low-dose vitamin D supplementation plays a big role in preventing breast cancer. Earlier studies have suggested that vitamin D may reduce breast cancer risk as breast cells have receptors for vitamin D which has raised the possibility that it could help regulate the division and proliferation of these cells.
The research team also noted that vitamin D assimilates very well when coupled with calcium, and vice versa, as the two elements work in tandem for maximum absorption. However they also noted that women’s dietary intake of vitamin D and calcium doesn’t seem to influence their risk of breast cancer, before or after menopause so presumably it is during that critical menopause period that this vitamin can be effective.
According to the study women who take at least 400 international units (IU) of vitamin D a day lower their risk of developing breast cancer by 24 percent. This level of vitamin D is the RDA (recommended daily allowance) but is now considered by many experts to be far too low and that to get a significant therapeutic effect from vitamin D, dosages upwards of 10,000 IU a day are far more appropriate.
In summer we get around 20,000 IU from the sun and our skin is fully capable of absorbing sunlight and processing it into vitamin D in just 15 to 30 minutes of exposure a day and so supplementing with vitamin D3 at a higher level than the RDA should certainly be safe up to this level in winter.