Calcitriol (1,25-dihydroxyvitamin D3) - a type of vitamin D has been known to inhibit the growth and stimulate the differentiation of prostate cancer cells.  A new study led by researchers at Stanford University School of Medicine now offers an explanation as to how vitamin D could ever fight prostate cancer.

The study finds that calcitriol is able to significantly decrease the expression of the gene that dictates the production of the enzyme known as cyclooxygenase-2 (COX-2), which is involved in the synthesis of prostate-cancer promoting prostaglandins.

Also calcitriol is found to increase the expression of the gene that is responsible the enzyme called 15-prostaglandin dehydrogenase (15-PGDH), which functions to inactivate cancer-promoting prostaglandins.

The Stanford researchers believe that this dual action of calcitriol reduces the concentrations of bio-active prostaglandins in prostate cancer cells, which promotes the proliferation and growth of prostate cancer.

The current study suggests that calcitriol can be used together with non-steroidal antiinflammatory medications that inhibit COX activity to improve the effectiveness of both drugs in the treatment of prostate cancer.

Calcitriol, also known as 1,25-dihydroxycholecalciferol or 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3 or 1,25(OH)2D) is the most potent metabolite of vitamin D.  This vitamin D metabolite was was first identified in 1971 by Michael F. Holick, a vitamin D expert at Boston University.

The most commonly form of vitamin D on the market is vitamin D3, but not calcitriol.  But physicians may prescribe calcitriol to treat various diseases including hypocalcaemia, hypoparathyroidism, osteomalacia in adults, rickets in infants and children, renal osteodystrophy, chronic kidney disease, and osteoporosis.

If vitamin D3 is taken to prevent or treat cancer, a dose of 70 to 100 ng per ml of blood is needed.  (David Liu)