Researchers assessed 10,578 pre-menopausal and 20,909 post-menopausal women (average age 55.2, average BMI 25.9 kg per sq. m) using a questionnaire about their medical history and lifestyle, plus a 131-item food frequency questionnaire (FFQ) to detail food, beverage and supplement consumption during the previous year.
Over an average of 10 years of follow-up, the researchers documented 276 cases of breast cancer in pre-menopausal women and 743 cases in postmenopausal women. Among the pre-menopausal women, calcium and vitamin D intake were associated with a 39 and 35 per cent lower risk of breast cancer respectively, comparing the highest with the lowest intakes. No such benefits were observed in post-menopausal women.
"A possible explanation for the evident difference by menopause status may be related to the joint relationship among calcium, vitamin D and insulin-like growth factors (IGFs)," wrote the researchers in Archives of Internal Medicine.
"In vitro studies have suggested that calcium and vitamin D exert anticarcinogenic effects on breast cancer cells expressing high levels of IGF-1 and IGF binding protein 3. Calcium, vitamin D and IGF binding protein 3 have been shown in vitro to interact with each other in promoting growth inhibition in breast cancer cells," they added.
Since blood levels of these compounds decline with age, they would be more prevalent in younger, pre-menopausal women, they said.
Steve - keep in mind that this is a was a food frequency questionnaire study, so it must be accepted with caution. However, we see yet again the importance of adequate vitamin D, especially as a complement to calcium.