We are posting a growing number of articles and reports relating to vitamin D and health. Ongoing research is revealing so many key biochemical roles for this nutrient we feel duty bound to report them as they are published. For some time clinicians have noted that vitamin D may reduce breast cancer risk. The latest study in this area now suggests that this occurs through an effect on steroid hormones in normally cycling (menstrual cycle) women. The study was conducted to determine whether there was an association between circulating vitamin D and estradiol and progesterone in young women. Volunteer women aged 18-22 (not using hormonal contraceptives) were recruited during summer and winter. They provided lifestyle information and a blood sample. The women recruited in winter gave a second sample after taking vitamin D supplement for 4 weeks. There were 101 women sampled during the luteal phase (1-14 days prior to the start of the next menstrual period).
The results of this study indicated that as vitamin D levels increased there was an associated decrease in progesterone and estradiol after adjustment for age, body mass index, ethnicity, season, alcohol use, smoking, and physical activity. The study concluded that higher levels of vitamin D may reduce progesterone and estradiol, providing a potential mechanism for reduction in breast cancer risk from increased vitamin D exposure in young women.
Vitamin D association with estradiol and progesterone in young women. Cancer Causes Control. 2010 Mar;21(3):479-83.