Studies have linked the risk factors for prostate cancer and those conditions leading to vitamin-D deficiency, such as aging. The relationship between vitamin-D levels and subsequent risk of prostate cancer is a confusing one. Low levels have been associated with the development of more aggressive prostate cancer. In another study, increased cancer risk existed in those with very low levels — but also high levels. But know this: high-dose vitamin D has been added to traditional chemotherapy to treat androgen-independent prostate cancer with some success.
In a large population study involving over 88,000 women for 16 years, vitamin D was linked with a significantly lower breast cancer risk in premenopausal women. Researchers pooled data from the literature to study the dose-response association between the vitamin and the disease:
– Those who were vitamin-D sufficient had a 50% lower risk of breast cancer than those who were vitamin-D deficient.
– Maintaining good levels of vitamin D to the point of preventing cancer requires a daily intake of 4,000 IU, which exceeds the National Academy of Science’s upper limit of 2,000 IU a day.
It is therefore not surprising to learn that, when 36,282 postmenopausal women were randomly assigned to receive 1,000 mg of calcium and 400 IU of vitamin D3 or placebo for seven years, there was no difference in the invasive breast cancer incidence. In the future, large, well-designed clinical trials are needed to address the important question of whether or not high-dose vitamin D could prevent breast cancer.
From a study with over 120,000 men and women, men with the highest vitamin-D intakes (from foods and supplements) had a 29% lower colorectal cancer risk as compared to men with the lowest vitamin-D intakes. In this study, there was no association between vitamin-D intake and colorectal cancer in women. Vitamin D was found to lower the risk of precancerous colorectal polyps.
But, a double-blind, placebo-controlled study involving 36,282 postmenopausal women, of which 18,176 women got 500 mg of calcium plus 200 IU of vitamin D3 twice a day and 18,106 received a matching placebo for seven years, failed to show any effect on the incidence of colorectal cancer. This study was criticized for using a dose of vitamin D too low to exert any effect on cancer. It was suggested that a daily intake of 1,000 IU of vitamin D would be needed in order to lower the risk of colorectal cancer.
It is critically important that future, well-designed randomized clinical trials be done before we can be certain whether or not vitamin-D supplementation has a protective role against colorectal cancer in men — and its effect on cancer overall.