Circulating 25-Hydroxyvitamin D and Risk of Pancreatic Cancer, American Journal of Epidemiology, 2010
"A high 25(OH)D concentration (≥100 nmol/L) was associated with a statistically significant 2-fold increase in pancreatic cancer risk."Cancer risk was higher in Caucasians and those living at latitudes above 35ºN. Interestingly, "few participants residing at low latitudes had 25(OH)D concentrations greater than 100 nmol/L."
That form of vitamin D, 25(OH)D, is an indicator of vitamin D status in the body. It comes from a blood test. It's not the vitamin D we eat, it's not the vitamin D we make in our skin, and it's not the active form of the vitamin. It's an intermediate that we measure to test for deficiency.
While 100 nmol/L is high, it's not that high:
"The range of 25(OH)D3 levels associated with risk in this study was below that considered to reflect hypervitaminosis D (400-1,250 nmol/L)."This particular study pooled results of several studies, 8 to be exact. The advantage of this ... it covered more geographical regions, had a larger number of cancer cases, and a wider range of vitamin D concentrations than the individual studies alone. You get a better feel for viable associations.
In one separate study of male Finnish smokers, "prediagnostic serum concentrations greater than 65.5 nmol/L were associated with nearly a 3-fold increased risk of pancreatic cancer."1 However, you can't generalize those results to women, to men younger than 50, or to populations outside Finland. Although these results are pretty ominous for men over 50 who smoke and who live at higher latitudes.
"The active form of vitamin D might influence growth factors (ref. given) which promote tumor growth (ref. given)."Active vitamin D is a steroid hormone. It affects a number of other regulators and hormones. Much of its influence has been discovered in only the last few decades. The manner of that influence is still in many cases a mystery.
Why The Pancreas?
The islet cells in the pancreas (if you have diabetes you may know that beta cells, part of the islet cell group, make insulin) make the particular enzyme that turns 25(OH)D3 into its active form 1,25(OH)D3. Not many cells make this enzyme. I know the kidney makes it. I'll have to be on the lookout for studies linking vitamin D to renal cancer.
"Given the present study's pooled results and research gaps in the understanding of vitamin D's role in carcinogenesis, recommendations to increase vitamin D concentrations in healthy persons for cancer prevention seem premature."