It also showed that in women who consumed high levels of calcium from both diet and supplements, the risk reduction was almost double that observed for calcium from either source by itself.
The results, published in this month's Cancer Epidemiology, Biomarkers and Prevention (vol 14, pp126-132), confirm previous findings demonstrating an association between calcium intake and protection against the disease.
Last year researchers found higher consumption of milk and overall calcium intake to be associated with a lower risk of the cancer in an analysis of around half a million subjects.
Calcium supplements have also been shown to cut the risk of colorectal polyps, tumours on the inside lining of the colon that can become cancerous.
In the new study, researchers from the University of Minnesota Cancer Center selelcted 45,354 women from the Breast Cancer Detection Demonstration Project (BCDDP), a breast cancer screening programme conducted jointly by NCI and the American Cancer Society between 1973-1980.
The women, without a history of colorectal cancer, were categorized into groups according to information they provided about their diets and lifestyles and were followed for an average of 8.5 years. Their average age was 62 years old.
Women in the highest group of dietary calcium intake - greater than 830 mg per day - had a 26 per cent lower risk of developing colorectal cancer compared to women in the lowest group, and those who consumed 800 mg daily of calcium from supplements had a 24 per cent lower risk of developing colorectal cancer than women who took no calcium from supplements.
But women who consumed more than 412.4 mg per day of calcium from diet and also consumed more than 800 mg from supplements had a 46 per cent lower risk of colorectal cancer than women who consumed less than these amounts.
"It is especially notable that the risk reduction was present regardless of the source of the calcium, and that simultaneously consuming high levels of calcium from both diet and supplements further reduced risk," said study leader Andrew Flood.
"These observations suggest that it was the calcium per se, and not merely dairy products or some other variable that accounted for the reduction in risk."
Approximately 150,000 people in the US are diagnosed with colorectal cancer each year. The cancer is the second leading cause of cancer death, and the risk of contracting it increases with age.
However researchers still do not understand why and how calcium provides protection against colorectal cancer in some women.
"There are currently two main theories. One is that calcium has the ability to neutralize secondary bile acids that are produced during the digestion of fat and are highly irritating to the cells in the lining of the colon. The evidence in support of this theory is not very strong."
"An alternate theory is that calcium has a direct impact on a whole series of biochemical pathways within the cells that line the colon and rectum. These pathways play important roles in regulating how these cells grow and mature and thus, can be important components of the cancer process."
The study adds to knowledge about the amount of calcium that offers protection - Flood suggests that a diet providing at least 800mg per day is an effective way for women to help guard against colorectal cancer.
The benefit is also likely to be seen in men, although dairy foods, the primary source of calcium in the western diet, have been linked in some studies to increased risk of prostate cancer, warned the researcher.