Based on the results of two separate studies, raising vitamin D levels may prevent up to half of all breast and two thirds of colorectal cancer cases. The researchers recommend a daily intake of 2000 IU of vitamin D3 and, when possible, moderate sun exposure.

Inadequate photosynthesis or oral intake of vitamin D is associated with high incidence and mortality rates of breast cancer.

Cedric Garland, DrPH, of the University of California at San Diego, and his team pooled dose-response data from 2 previous studies (the Harvard Nurses’ Health Study and the St.George's Hospital Study). They divided more than 1700 records in the studies into 5 groups from the lowest blood levels of 25-hydroxyvitamin D (< 13 ng/mL) to the highest (approximately 52 ng/mL). The investigators found that patients with serum concentration of 25-hydroxyvitamin D of approximately 52 ng/mL had a 50% lower risk of breast cancer than those with serum measuring less than 13 ng/mL. This level corresponds to a vitamin D intake of 4000 IU per day (this exceeds the National Academy of Science upper limit of 2000 IU per day). The researcher are building a case to have this level increased, but in the meantime until further studies are made, they recommend a daily intake of 2000 IU. The group is also calling for an additional 10 to 15 minutes of daily sun exposure when appropriate (an amount estimated to be equivalent to an oral intake of 3000 IU of vitamin D3). It should be pointed out that sun exposure is inadvisable for patients with primary photosensitivity disorder, people taking photosensitizing medications, and anyone with a personal or close family history of skin cancer or actinic keratosis.

Raising the serum level of 25-hydroxyvitamin D to 34 ng/mL would reduce the incidence rates of colorectal cancer by half.

In a second study (lead author was Edward Gorham, MPH, PhD, researcher epidemiologist at Naval Health Center in San Diego) researchers conducted a meta-analysis of 5 studies examining serum concentration of 25-hydroxyvitamin D in colorectal cancer. There were 535 cases and 913 controls (1448 participants in total). The investigators divided the results into quintiles with median 25-hydroxyvitamin D values of 6, 16, 22, 27 and 37 ng/mL. They found that raising the serum level of 25-hydroxyvitamin D to 34 ng/mL would reduce the incidence rates of colorectal cancer by half, and with serum levels of 46 ng/mL for 67 per cent. Daily intake of 1000 to 2000 IU would be protective against colorectal cancer and would not pose any risk for most people.

Sources: Vitamin D Appears to Cut Breast and Colorectal Cancer Risk (Medscape), Ordinary Doses of Vitamin D Linked to Lower Mortality (Medscape).