Higher predicted plasma levels of vitamin D may reduce the risk for incident Crohn’s disease by half in women, reported Dr. Ashwin N. Ananthakrishnan and colleagues in the March 1 issue of Gastroenterology.
"Our results strengthen the rationale for considering vitamin D supplementation both for treatment of active CD or prevention of disease flares," wrote the authors (Gastroenterology 2012 [doi:10.1053/j.gastro.2011.11.040]).
Additionally, "our data suggest a possible role for routine screening for vitamin D deficiency or vitamin D supplementation among individuals at high risk for development of CD."
Dr. Ananthakrishnan of Harvard Medical School, Boston, analyzed data from 1,492,811 person-years of follow-up in the Nurses' Health Study, a prospective cohort begun in 1976.
For the study, the authors focused on data from the 72,719 women (median age at baseline, 53 years) who returned the 1986 questionnaire, which included data on dietary intake and physical activity.
Subjects had no prior history of CD, ulcerative colitis (UC), or cancer (except nonmelanoma skin cancer). Plasma 25(OH)D was derived using a previously published, validated regression model that includes vitamin D intake from diet and supplements, sun exposure, race, and body mass index (J. Natl. Cancer Inst. 2006;98:451-9).
When a new diagnosis of either CD or UC occurred, subjects were contacted and sent a supplemental questionnaire, and their medical records were reviewed by the researchers.
Overall, there were 122 cases of CD and 123 cases of UC documented from 1986 through June 30, 2008, with a median age at diagnosis of 64 years for CD and 63.5 years for UC.
The authors then stratified the women into quartiles based on predicted plasma 25(OH)D levels.
They found that, compared with women in the lowest quartile, women in the highest two quartiles had a significantly lower risk of CD, with a multivariate hazard ratio (HR) of 0.50 in the highest quartile (95% confidence interval, 0.28-0.90), and an HR of 0.55 in the second-highest quartile (95% CI, 0.30-1.00).
For UC, there was also a lower risk among women in the highest quartile, although it did not reach significance (HR, 0.68; 95% CI, 0.5-1.31).
Next, the authors examined the associations between risk for CD and UC and predefined 25(OH)D levels. Values greater than or equal to 30 ng/mL were defined as vitamin D sufficiency; values between 20 ng/mL and 30 ng/mL were defined as insufficiency, and values less than 20 ng/mL were classified as deficiency.
"Compared to women who were predicted to be vitamin D deficient, the multivariate HR of CD was 0.38 (95% CI, 0.15-0.97) for women predicted to be vitamin D sufficient," wrote the authors.
"The corresponding multivariate HR of UC was 0.57 (95% CI, 0.19-1.70) for women predicted to be vitamin D sufficient," they added.
Finally, looking at the findings another way, the authors calculated that for each 1 ng/mL increase in plasma 25(OH)D, there was a 6% relative reduction in risk of CD (multivariate HR, 0.94; 95% CI 0.89-0.99) and a nonsignificant 4% reduction in risk of UC (multivariate HR, 0.96; 95% CI 0.91-1.02).
Vitamin D intake from diet and supplements was also related to risk of CD and UC, with a 10% reduction in UC risk and a 7% reduction in CD risk for every 100 IUs consumed per day.
The authors conceded the possibility that women who take vitamin D supplements may be more likely to engage in other healthy behaviors that would minimize their likelihood of developing UC or CD.
"However, vitamin D supplement intake is only a minor determinant of vitamin D status," the authors wrote, with more than 50% of plasma 25(OH)D levels attributable to conversion in the skin.
Moreover, "compared to the lowest level of vitamin D supplement intake, intake of greater than 400 IU/day of vitamin D supplements increased plasma 25(OH)D by less than 1 ng/mL," they added.
"Thus, our overall associations with vitamin D status are unlikely to be attributable to differing propensity to use dietary supplements."
The authors reported that the study was supported by a grant from the American Gastroenterological Association and the Broad Medical Research Foundation. Two authors disclosed financial relationships with companies including Proctor & Gamble, Shire Pharmaceuticals, Cytokine Pharma, Warner Chilcott, Bayer HealthCare, and Millennium Pharmaceuticals.
Dr. Ashwin Ananthakrishnan
© Kaspri/Fotolia.com
Vitamin D supplements can lead to a greatly decreased risk of Crohn’s disease in women.