Can Vitamin D Prevent Breast Cancer?

Breast cancer is the most common cancer among women worldwide after skin cancer. According to the American Cancer Society, almost half of those diagnosed with breast cancer will die within 20 years. Despite advances in treatment, breast cancer remains a frightening diagnosis that no woman wants to hear.

Is it possible to prevent breast cancer? Numerous studies seem to indicate that vitamin D may play a role in protection against breast cancer as well as possibly prevent metastasis (spread) of the cancer once it has been diagnosed.

Researchers examining two research studies by the Harvard Nurses Health Study and the St. George's Hospital Study, concluded that supplemental vitamin D₃ (in the form of cholecalciferol) may reduce breast cancer risk by 50%. The vitamin can come in supplemental form at 4,000 IU per day, or 2,000 IU per day plus about twelve minutes daily spent in the sun. In these two studies, which involved almost 1,800 patients, those with the highest risk for breast cancer had the lowest blood levels of vitamin D.

Another study of 31,000 women from Brigham and Women's Hospital and Harvard Medical School seemed to indicate that dietary vitamin D along with calcium led to a slightly lower risk of breast cancer, but only in premenopausal women, and had greater effect on aggressive tumors. It could be that older women have a greater need more vitamin D and calcium.

Vitamin experts are in agreement that the current dietary recommendations for vitamin D are too low and should be raised to between 1,000 IU and 1,500 IU a day, with the caveat that too much vitamin D is toxic.

Vitamin D can be obtained from foods like dairy and fish, but as little as ten minutes in the sun without sunscreen and with 40% of the body exposed can produce adequate vitamin D in the body through a chemical reaction aided by ultraviolet rays.

It is postulated that vitamin D helps maintain healthy cells and discourages uncontrollable cell reproduction typical of cancer. It also helps prevent the new blood vessels that tumors feed off of.

In another study of 279 women with metastatic breast cancer, blood levels of vitamin D were higher in those who had early-stage breast cancer than those who had later-stage cancer.

It has also been known that in lower latitudes with more sunlight there is a lower incidence of breast cancer.

What is yet unknown is whether low vitamin D levels actually cause advanced disease, or whether advanced disease leads to reduced dietary intake of vitamin D or less sun exposure.

In the absence of definitive proof that vitamin D prevents breast cancer or reduces metastasis, the wisest course for a woman to take who wants to avoid breast cancer or prevent its spread is to increase her intake of vitamin D through supplementation and modest sun exposure. But always check with your physician first before taking high-dose vitamins or increasing your time in the sun.