Previously, two small studies of vitamin D levels and subsequent risk of pancreatic cancer showed a U shaped curve; people with the lowest and the highest vitamin D being at increased risk. Last month researchers at the Dana-Farber Cancer Institute and Harvard University, led by Dr. Brain Wolpin and Professor Charles Fuchs, did a meta-analysis of five large studies of vitamin D levels and pancreatic cancer.
Wolpin BM, Ng K, Bao Y, Kraft P, Stampfer MJ, Michaud DS, Ma J, Buring JE, Sesso HD, Lee IM, Rifai N, Cochrane BB, Wactawski-Wende J, Chlebowski RT, Willett WC, Manson JE, Giovannucci EL, Fuchs CS. Plasma 25-Hydroxyvitamin D and Risk of Pancreatic Cancer. Cancer Epidemiol Biomarkers Prev. 2011 Dec 7. [Epub ahead of print]
The results showed the higher your vitamin D levels the lower your risk for pancreatic cancer and that included people with levels greater than 40 ng/ml. No U shaped curve. More and more it looks as if Professor Reinhold Vieth is right (again) in his theory that high intermittent yearly doses of vitamin D (summer) followed by many months of deficiency (fall winter and early spring) resets the intracellular enzymes that help prevent cancer. Take your vitamin D daily, or at least weekly if you must, but not monthly.
The take away from this paper is simple. Keep you 25(OH)D level at 50 ng/ml if you are healthy and around 80 if you have a vitamin D related disease like cancer, autism, astma, or heart disease. I am not aware of any evidence that a level of 80 ng/ml will help you if you have a potentially fatal illness like cancer, but there is no apparent harm of a level of 80 ng/ml, and there may be benefits unstudied to date. Thus a risk/benefit analysis favors 80 ng/ml. However keep in mind, once the cancer has destroyed the vitamin D system inside the cancer cells, all the vitamin D in the world is not going to put that vitamin D system together again.