The study, published on May 28, 2007 in the Archives of Internal Medicine, tracked the health of over 10,000 (10,578) pre-menopausal women, and over 20,000 (20,909) post menopausal women over the course of 10 years. The top fifth of the pre-menopausal women who had the highest intake of Vitamin D and calcium (1,366 milligrams of calcium and 948 units of Vitamin D) had a one-third reduced risk compared with those who consumed the least.
Occurrences of breast cancer in pre-menopausal women aren't very common. Less than 5% of Breast Cancer cases occur in women under the age of 40, and they comprise less than 3% of deaths from breast cancer. Still, getting an optimal daily intake of Calcium and Vitamin D isn't a bad thing; both play a role in preventing osteoporosis, may aid in weight loss, and have other heath benefits.