Vitamin D Deficiency Worsens Breast Cancer?

May 16, 2008 -- Vitamin D deficiency is common among women diagnosed with breast cancer, and it may raise the risk of cancer spread and death, researchers report.

In a new study, women with vitamin D deficiency at the time of breast cancer diagnosis were 94% more likely to experience cancer spread and 73% more likely to die over the next 10 years, compared to women with adequate vitamin D levels.

More than 1 in 3 women studied had a vitamin D deficiency.

The study is the first to suggest a link between vitamin D deficiency and breast cancer progression, but it doesn't prove cause and effect. And it's too soon to recommend that all women with breast cancer start taking supplements to improve their outlook, says study head Pamela Goodwin, MD, professor of medicine at the University of Toronto.

But "women with breast cancer may want to get their vitamin D levels checked in a blood test and get them into the healthy optimal range," she tells WebMD.

The findings are scheduled to be reported at the annual meeting of the American Society of Clinical Oncology in Chicago.

Vitamin D Puts Brakes on Breast Cancer

Vitamin D is found in some foods, especially milk and fortified cereals, and is made by the body after exposure to sunlight. It is necessary for bone health, and some studies suggest that it may protect women from developing breast cancer in the first place.

From a biological point of view, it makes sense that vitamin D would put the brakes on breast cancer development and spread, Goodwin says.

"Breast cancer cells have vitamin D receptors, and when these receptors are activated by vitamin D, it triggers a series of molecular changes that can slow down cell growth, cause cells to die, and make the cancer less aggressive," she says.

For the new study, Goodwin and colleagues measured vitamin D levels in the blood of 512 women diagnosed with breast cancer in Toronto between 1989 and 1995. They were followed for a median of 12 years.

Only 24% had adequate levels of vitamin D when they were diagnosed with cancer. A total of 37.5% were deficient in vitamin D. The other 38.5% had insufficient levels of vitamin D.

Of note, Goodwin says, is that women with vitamin D deficiency were more likely to have aggressive cancers than those with sufficient levels.

Vitamin D Deficiency Linked to Poor Breast Cancer Prognosis

After 10 years, 83% of women with adequate levels were alive without signs of cancer spread (metastasis) vs. only 69% of women with vitamin D deficiency. Most of the deaths were from breast cancer.

For women with insufficient levels of vitamin D, there was a slightly increased risk of cancer spread compared to women with sufficient levels, but the difference was so small it could have been due to chance. "And their risk of death was the same," Goodwin says. "So the majority of the [negative] effect is in women with a deficiency."