There are around 115,000 people in the United Kingdom suffering with Crohn's Disease (CD). CD can cause inflammation and ulcers to develop anywhere within the gut. Symptoms of the disease include diarrhoea, abdominal pain and nutritional problems including vitamin D deficiency. Around half of people with CD are likely to have vitamin D deficiency. Research has shown that treating vitamin D deficiency in people with CD might help to improve the symptoms of the disease. However, there are no clear guidelines on how to detect or treat vitamin D deficiency in people with CD.

There will be two parts to the planned research involving three hospitals in Birmingham. Part 1 is a vitamin D screening study, where adults will be asked to have a finger-prick blood test to check their vitamin D levels. They will complete short diet and lifestyle questionnaires. Adults found to have vitamin D deficiency in part 1 may be invited to join part 2 of the research. Part 2 is a vitamin D supplementation study where participants will be given a daily vitamin D capsule to take by mouth for 6 months. They will be randomly allocated to 2 different groups with each group receiving a different dose of vitamin D. Participants will have blood tests at the start, after 3 months and after 6 months. They will complete quality of life questionnaires at the start and after 6 months. The last appointment will be a final follow up appointment after 9 months.

This research is important to help determine:

• Which dose of vitamin D is most effective at treating vitamin D deficiency in people with CD
• If symptoms of CD improve when vitamin D deficiency is treated.

Inclusion Criteria:

1. VITAMIN D SCREENING STUDY

   Those:

   • With a confirmed diagnosis of Crohn's Disease (CD)
   • ≥ 18 years of age
   • Have provided written informed consent

2. VITAMIN D SUPPLEMENTATION FEASIBILITY TRIAL

Those:

• With a confirmed diagnosis of CD
• Identified as having Vitamin D deficiency < 50 nmol/L in the Winter screening study
• ≥ 18 years of age
• Already receiving treatment for CD as per National Institute for Health and Care Excellence (NICE) Guidance or those in remission and not currently receiving treatment but who continue to attend hospital out-patient appointments
• Have provided written informed consent

Exclusion Criteria:

1. VITAMIN D SCREENING STUDY

   • None

2. VITAMIN D SUPPLEMENTATION FEASIBILITY

Those:

• Currently receiving vitamin D, fish oil or multi-vitamin supplementation and unwilling to stop this to participate in the feasibility trial

• Currently receiving:

  • Bisphosphonates
  • Digitalis or other cardiac glycosides
  • Phenytoin
  • Barbituates (e.g. Amylobarbitone, Butobarbitone, Methyl Phenobarbitone, Pentobarbitone, Quinalbarbitone, Amylobarbitone)
  • Actinomycin
  • Imidazole

• With known hyperparathyroidism

• With known sarcoidosis

• With known renal disease or kidney stones

• With known hypercalcaemia (corrected serum calcium ≥2.60 mmol/L)

• With known underlying liver disease

• With known hypersensitivity to vitamin D supplements or any of the trial medication excipients

• Who are pregnant, breast feeding, trying to conceive or women of child-bearing age who decline to have a pregnancy test where applicable. Women who have had a hysterectomy, bilateral oophorectomy or early menopause will not require a pregnancy test.

• Individuals who have participated in a trial testing a medicinal product within 6 months preceding screening