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Vitamine D tegen darmkanker en doodgaan*
Uit twee studies blijk weer eens het belang van goede bloedwaarden vitamine D. Uit een Duitse analyse van 14 studies onder ruim zestigduizend mensen blijkt dat zij met de hoogste bloedwaarden vitamine D tot wel 30% minder kans hebben om dood te gaan. Als bloedwaarden vitamine D onder 30 ng/ml dalen stijgt de kans op doodgaan lineair met deze daling.
Uit een Japanse studie onder 1.440 deelnemers, waarvan de helft met darmkanker blijkt dat zij met de hoogste gemiddelde bloedwaarden van 32 ng/ml vitamine D wel 36% minder kans op darmkanker dan zij met de laagste bloedwaarden (gemiddeld 16 ng/ml). Inname van voeding met dagelijks gemiddeld 590 mg calcium bleek de kans op darmkanker met 37% te verminderen
Vitamin D deficiency and mortality risk in the general population: a meta-analysis of prospective cohort studies.
Zittermann A, Iodice S, Pilz S, Grant WB, Bagnardi V, Gandini S.
Source: Clinic for Thoracic and Cardiovascular Surgery, Heart Centre North Rhine-Westphalia, Ruhr University Bochum, Bad Oeynhausen, Germany.
Abstract
BACKGROUND: 
Low vitamin D status may increase mortality risk.
OBJECTIVE: 
We used nonparametric ("highest compared with lowest" categories) and parametric (>2 categories) statistical models to evaluate associations of 25-hydroxyvitamin D [25(OH)D] serum concentrations and mortality in observational studies among general populations.
DESIGN: 
We searched PubMed, EMBASE, Web of Science, and reference lists for relevant articles. We included studies that contained data on relative risks (RRs) for mortality for different 25(OH)D concentrations, which included a corresponding measure of uncertainty, and this yielded 14 prospective cohort studies that involved 5562 deaths out of 62,548 individuals. We applied log-transformed RRs and CIs, adjusted for the maximal number of confounding variables. In the parametric model, which is based on 11 studies and 59,231 individuals, we used the lowest quantile as the reference category.
RESULTS: 
For "highest compared with lowest" categories of 25(OH)D, the estimated summary RR of mortality was 0.71 (95% CI: 0.50, 0.91). In the parametric model, the estimated summary RRs (95% CI) of mortality were 0.86 (0.82, 0.91), 0.77 (0.70, 0.84), and 0.69 (0.60, 0.78) for individuals with an increase of 12.5, 25, and 50 nmol 25(OH)D serum values/L, respectively, from a median reference category of ∼27.5 nmol/L. There was, however, no significant decrease in mortality when an increase of ∼87.5 nmol/L above the reference category occurred.
CONCLUSION: 
Data suggest a nonlinear decrease in mortality risk as circulating 25(OH)D increases, with optimal concentrations ∼75-87.5 nmol/L.

Association Between Plasma 25-Hydroxyvitamin D and Colorectal Adenoma According to Dietary Calcium Intake and Vitamin D Receptor Polymorphism 
1. Taiki Yamaji*, 2. Motoki Iwasaki, 3. Shizuka Sasazuki, 4. Hiromi Sakamoto, 5. Teruhiko Yoshida and 6. Shoichiro Tsugane
1. ↵*Correspondence to Dr. Taiki Yamaji, Epidemiology and Prevention Division, Research Center for Cancer Prevention and Screening, National Cancer Center, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan (e-mail: tyamaji@ncc.go.jp). 
Abstract
The anticarcinogenic potential of vitamin D might be mediated by not only calcium metabolism but also other mechanisms initiated by vitamin D receptor (VDR). The authors measured plasma 25-hydroxyvitamin D in healthy volunteer examinees who underwent total colonoscopy in Tokyo, Japan, 2004–2005, and evaluated its influence on colorectal adenoma, both alone and in interaction with VDR polymorphisms, which correspond to the FokI and TaqI restriction sites. The main analysis of plasma 25-hydroxyvitamin D included 737 cases and 703 controls. Compared with the lowest quintile of plasma 25-hydroxyvitamin D, only the highest was related to a significantly decreased odds ratio of colorectal adenoma (odds ratio = 0.64, 95% confidence interval: 0.45, 0.92). In contrast, all but the lowest quintile of dietary calcium intake presented similarly reduced odds ratios (odds ratio for the highest = 0.67, 95% confidence interval: 0.47, 0.95). Of note, the association between plasma 25-hydroxyvitamin D levels and colorectal adenoma was modified by the TaqI polymorphism of the VDR gene (Pinteraction = 0.03) but not by dietary calcium intake (Pinteraction = 0.93). These observations highlight the importance of vitamin D in colorectal tumorigenesis. Vitamin D might protect against colorectal neoplasia, mainly through mechanisms other than the indirect mechanism via calcium metabolism. (Februari 2012)