BAKERSFIELD, Calif. -- Vitamin D, found in milk, eggs, fish, and exposure to sunlight, is well known to play an essential role in cell growth, in boosting the body's immune system, and in strengthening bones.

Women with breast cancer are even more likely to have low levels of vitamin D and this can contribute to accelerated bone loss and an increased risk for bone fractures.

Researchers at the University of Rochester tested vitamin D levels in 166 women undergoing breast cancer treatment and found that 70 percent of them had low levels of vitamin D. For those with late-stage breast cancer, average levels were even lower.

In order to bring patients' vitamin D levels up to an optimal level, researchers gave them high doses of vitamin D supplements equivalent to more than 10 times the recommended value for healthy individuals. These high doses, when given weekly, were able to improve vitamin D levels for these patients.

Given these findings, researchers recommended that women with breast cancer work with their doctors to safely increase their intake of vitamin D as excessive doses of this nutrient can be toxic.