A four year clinical study was done involving 1200 women. A group was assigned to take 1400 mg of calcium alone. Another group was assigned to take 1100 IU of vitamin D along with 1400 mg of calcium. The study showed a 60% decrease in the development of any cancers in the vitamin D group. If you excluded the number that developed cancer in the first year, since it is likely the cancer was already developing, the study showed over a 77% reduction.