
Overall, while there was no link between breast cancer and vitamin D from food, pre- and post-menopausal women who took a vitamin D supplement of more than 400 IU per day were 24 percent less likely to develop breast cancer compared to women who did not take a vitamin D supplement.
Although the study could not measure vitamin D in adolescence, researchers suggested that taking a vitamin D supplement during these formative years may be the most important factor in preventing breast cancer.