Calcium Plus Vitamin D Supplementation and the Risk of Breast Cancer
Randomized trial
Link: http://jnci.oxfordjournals.org/content/100/22/1581.long
From conclusions:
“Calcium and vitamin D supplementation did not reduce invasive breast cancer incidence in postmenopausal women.”
Doses too low (they spend some text on this in the discussion section—even the 800 IU they say some participants got is probably too low). They don’t seem to measure the effect of the supplement on serum levels. They compute baseline serum level vs chance of getting cancer but they should really have monitored their participants.
Seriously. If you supplement, you should check that your supplement actually is effective or you fail to create the desired condition to test.