Association between higher predicted serum vitamin D levels and reduced incidence of IBD.

[kiny]

If this has already been posted, please delete the thread, I just don't seem to see a thread about it atm.

Full http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3367959/

2012 March

Ashwin N. Ananthakrishnan,* Hamed Khalili,* Leslie M. Higuchi,‡ Ying Bao,§ Joshua R. Korzenik,* Edward L. Giovannucci,‖ James M. Richter,* Charles S. Fuchs,§¶ and Andrew T. Chan*§



BACKGROUND & AIMS:

Vitamin D influences innate immunity, which is believed to be involved in the pathogenesis of Crohn's disease (CD) and ulcerative colitis (UC). However, data examining vitamin D status in relation to risk of CD and UC are lacking.

METHODS:

We conducted a prospective cohort study of 72,719 women (age, 40-73 y) enrolled in the Nurses' Health Study. In 1986, women completed an assessment of diet and lifestyle, from which a 25-hydroxy vitamin D [25(OH)D] prediction score was developed and validated against directly measured levels of plasma 25(OH)D. Through 2008, we confirmed reported diagnoses of incident CD or UC through medical record review. We used Cox proportional hazards modeling to examine the hazard ratio (HR) for incident CD or UC after adjusting for potential confounders.

RESULTS:

During 1,492,811 person-years of follow-up evaluation, we documented 122 incident cases of CD and 123 cases of UC. The median predicted 25(OH)D level was 22.3 ng/mL in the lowest and 32.2 ng/mL in the highest quartiles. Compared with the lowest quartile, the multivariate-adjusted HR associated with the highest quartile of vitamin D was 0.54 (95% confidence interval [CI], 0.30-.99) for CD (P(trend) = .02) and 0.65 (95% CI, 0.34-1.25) for UC (P(trend) = .17). Compared with women with a predicted 25(OH)D level less than 20 ng/mL, the multivariate-adjusted HR was 0.38 (95% CI, 0.15-0.97) for CD and 0.57 (95% CI, 0.19-1.70) for UC for women with a predicted 25(OH)D level greater than 30 ng/mL. There was a significant inverse association between dietary and supplemental vitamin D and UC, and a nonsignificant reduction in CD risk.

CONCLUSIONS:

Higher predicted plasma levels of 25(OH)D significantly reduce the risk for incident CD and nonsignificantly reduce the risk for UC in women.

 

[kiny]

Dear Sir:

We read with great interest the paper by Ananthakrishnan et al1 reporting an association between higher predicted serum vitamin D levels and reduced incidence of inflammatory bowel diseases (IBD). The vitamin D hormone (1,25(OH)2D3) has modulating effects on the innate and adaptive immune responses.2 Moreover, vitamin D receptor signaling is also involved in the regulation of intestinal mucosal barrier function.3 As such, vitamin D may play an important role in disease onset as well as severity of inflammation in IBD. Although previous studies have demonstrated an association between low vitamin D status and bone disease in established or newly diagnosed patients with Crohn's disease (CD),4, 5, 6 this is the first large, prospective study to investigate vitamin D status and incidence of IBD.

Despite demonstrating a significant association of predicted vitamin D levels with CD and a nonsignificant association with ulcerative colitis, the authors may have underestimated the association in this study. There are two major factors that could have contributed to an underestimation. First, there was a small sample size of incident cases in this cohort. The patient population was significantly older than average for new diagnoses of IBD, which likely limited the number of incident cases identified in the cohort.7 The authors also excluded over half the patients with self-reported IBD in the cohort from their analysis. The second factor that may have contributed to underestimating the effect of vitamin D was using quartile averages for the primary comparison rather than comparing vitamin D–deficient patients to those without vitamin D deficiency. When examining patients who had predicted levels <20 ng/mL (deficient) compared with >30 ng/mL (sufficient), measurements that are commonly used in clinical practice, the hazard ratios for incidence of IBD were more robust (0.38 for CD; 0.57 for ulcerative colitis). Because there were wide confidence intervals with this comparison, the authors likely did not have the sample size to meet statistical significance and utilize this comparison for their primary analysis.

We congratulate the authors on this work and believe that these findings are timely and important. Because this study was based on predicted vitamin D values, larger prospective studies with serum vitamin D measurements are needed to confirm these conclusions.