It may be common for women with breast cancer to have low levels of vitamin D, according to a new British report.

Doctors tested 166 women with breast cancer. More than half of them had low levels of vitamin D.

"Women with breast cancer should be tested for vitamin D levels and offered supplements, if necessary," said researcher Sonia Li, M.D., of the Mount Vernon Cancer Centre in Middlesex, England. The findings were presented at the San Antonio Breast Cancer Symposium.

Some previous studies have also suggested a link between breast cancer and low vitamin levels. No studies, however, have proven the cause and effect.

Li said 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 cell growth and cause cells to die.

Vitamin D is in some food like milk and fortified cereals and it is made by the human body naturally after exposure to sunlight. However, the study showed no association between vitamin D levels and seasons.