25-hydroxyvitamin D-1 alpha-hydroxylase in normal and malignant colon tissue

Vitamin D affects calcium metabolism and prevents proliferation of colon ce lls in vitro. In human beings the main circulating form of vitamin D is 25- hydroxyvitamin D; to regulate calcium homoeostasis, this form must be conve rted to 1 alpha, 25-dihydroxyvitamin D by 1 alpha -hydroxylation in the kid ney with 25-hydroxyvitamin D-1 alpha -hydroxylase. Cultured transformed col on cancer cells can convert 25-hydroxyvitamin D-3 to 1 alpha ,25-dihydroxyv itamin D-3. We identified messenger RNA (mRNA) for 25-hydroxyvitamin D-1 al pha -hydroxylase in normal colon tissue and in malignant and adjacent norma l colon tissue. These findings support the notion that vitamin D might have a role in cell growth regulation and cancer protection, and might be the e xplanation for why the risk of dying from colorectal cancer is highest in a reas with the least amount of sunlight.