Determinants of vitamin D status in adult Crohn's disease patients, with particular emphasis on supplemental vitamin D use.

OBJECTIVE: To investigate determinants (pathophysiologic and physiologic, behavioural and lifestyle) of vitamin D status in Irish Crohn's disease (CD) patients.
DESIGN: A cross-sectional observational study.
SETTING: Cork City, Ireland (52 degrees N).
SUBJECTS: Crohn's Disease patients (n=58; mean age 38.1 years) were recruited from Cork University Hospital.
RESULTS: Fifty and nineteen percent of Irish CD patients were vitamin D deficient (defined by serum 25 hydroxyvitamin (OH) D levels <50 nmol/l) during winter and summer, respectively. Multiple regression analysis showed that summer-time serum 25 (OH) D levels were positively associated with use of vitamin D supplements (P=0.033) and negatively associated with smoking (P=0.006) and being male (P=0.063). During winter-time, use of vitamin D supplements (P=0.041) and sun habits (P=0.066) were positively associated, whereas small intestinal involvement (P=0.005) and body mass index (BMI) (P=0.083) were negatively associated with serum 25 (OH) D levels. There was no significant association between other non-pathophysiologic (age, dietary calcium or vitamin D) or pathophysiologic factors (steroid use, resection), and serum 25 (OH) D levels, at either season. Approximately 41 and 60% of the total variation in summer- and winter-time serum 25 (OH) D, respectively, was explained by this model.
CONCLUSION: A high proportion of Irish CD patents had some level of vitamin D deficiency (<50 nmol/l) during late-wintertime. Use of regular low-dose supplemental vitamin D, particularly by patients with small intestinal involvement, cessation of smoking and adequate, but responsible, exposure to summer sunlight as well as maintaining BMI in the normal range could help maintain adequate vitamin D levels during wintertime.