Key words: prostate cancer; 25(OH)-vitamin D 3 ; serum bankVitamin D deficiency has been implicated as risk factor for prostate cancer. 1 In cell culture studies, vitamin D metabolites have had protective action against cancer development (for review see Ylikomi et al. 2 ). Normal and malignant prostate cells contain vitamin D receptor (VDR), 3-5 which mediates the antiproliferative action of 1,25(OH) 2 -vitamin D 3 . 6 In addition to the antiproliferative action of 1,25(OH) 2 -vitamin D 3 , it can cause apoptosis, 7 induce differentiation, 8 inhibit telomerase expression, 9 inhibit tumor cell invasiveness 10 and suppress tumor-induced angiogenesis. 11 Several epidemiologic studies have reported that high serum vitamin D levels or sunlight may protect against prostate cancer. 3,4,[12][13][14][15] Factors that affect prostate cancer include age, dark skin and environment, e.g., latitude and diet. 16 These factors might be linked to vitamin D availability. 17,18 Furthermore, high fish (rich in vitamin D) consumption appears to correlate with lower prostate cancer risk. 19 In addition, VDR gene polymorphism may contribute to the risk of prostate cancer. 20 -24 There is also a study showing no correlation between serum vitamin D metabolites and prostate cancer in Maryland (USA), 25 but the authors concluded that the power of their study was limited. In another study on U.S. male physicians, only a weak protection against prostate cancer was found with the highest quartile of serum 1␣,25(OH) 2 -vitamin D 3 . 26 Similarly, no correlation was found in Hawaii. 27 There are 2 physiologically interesting metabolites of vitamin D, 1␣,25(OH) 2 -vitamin D 3 , regulating calcium homeostasis for bones and muscles in extremely narrow limits, and 25(OH)-vitamin D 3 , regulating target (prostate) cell proliferation and differentiation through activation to 1␣,25(OH) 2 -vitamin D 3 in the target (prostate) cell. Serum 25(OH)-vitamin D 3 is produced by liver 25-hydroxylase, the rate of the synthesis being directly proportional to vitamin D 3 serum concentration. 28 Therefore, serum 25(OH)-vitamin D 3 reflects vitamin D availability in the organism. Serum concentration of 25(OH)-vitamin D 3 is so high that it might possess a significant biologic activity in target cells, but it is also a precursor for the biologically more active 1␣,25(OH) 2 -vitamin D 3 . Prostate as well as many other target organs can activate 25(OH)-vitamin D 3 through 1␣-hydroxylation 29,30 and inactivate it through 24-hydroxylation. 31 In an epidemiologic study, we found that low concentrations (Ͻ40 nmol/l) of 25(OH)-vitamin D in serum were associated with a 1.7-fold increased risk of prostate cancer. 3,4 Since the power of our study was limited, preventing extensive analysis of the data, and we are partners in the Nordic Specimen Banks for Cancer Causes and Control, we had an opportunity to extend our study to other Scandinavian countries located geographically at the same latitude. Our aim was to determine whether our finding could be replicated in a la...

Vitamin D emerges as an important neurosteroid hormone in the brain, with a strong potential for age-specific applications in clinical nutrition.

Clinical trials of vitamin D supplementation are needed to investigate whether it enhances immunity to microbial infections.