Aims:Prospectively observe the effects of Vitamin D drops supplementation on the chronic course of Crohn's disease patients, analyze whether the effect of Vitamin D drops on CD patients is affected by factors such as disease site, disease activity, treatment, etc.Exploring the relationship between Fok I gene polymorphism and the efficacy of vitamin D supplementation. Provide a certain theoretical basis for "precision treatment" for CD patients in the future.

Design：It is a prospective cohort study. Investigators include a total of 60 participants with CD according to the inclusion and exclusion criteria, and divide them into two groups to assess their initial disease activity and detect related indicators. At the same time，investigators detect the Fok I gene polymorphism in all participants.One group is given Vitamin D drops 400IU per day orally, and the control group do not intervene. Participants' disease activity is assessed at baseline and related indicators are determined. The disease activity is re-evaluated at 2, 6, 14, 22, 30, and 38 weeks, and the serum indexes are re-evaluated.Investigators use statistical methods to analyze whether Vitamin D drops supplementation treatment can increase the serum 25 (OH) D level of CD participants who are treated with infliximab, improve the condition of CD participants,relationship with Fok I gene polymorphism，and analyze the effects of Vitamin D drops on participants with CD is affected by factors such as disease site, disease activity, and treatment.

1. The research can be started only after approval by the Medical Ethics Committee of the Second Affiliated Hospital of Wenzhou Medical University.

2. According to the "Consensus on Diagnosis and Treatment of Inflammatory Bowel Disease" formulated by the Beijing Conference in 2018 as a standard, patients with clear diagnosis of CD are collected. Other diagnostic criterions include vitamin D deficiency (<= 20ng / ml) and treatment with infliximab. Exclusion criteria include pregnancy, breastfeeding, liver and kidney dysfunction, concurrent autoimmune diseases, and use of antiepileptic drugs or drugs metabolized by liver cytochrome P450 enzymes.

3. Assess disease activity of CD participants based on the "Simplified Crohn's disease Activity Score".

4. General information about participants with CD is collected.

5. Detection of Fok I gene polymorphism using Snapshot technology.

6. The level of serum 25 (OH) D of participants is detected.

7. Serum C-reactive protein, erythrocyte sedimentation rate, albumin, calcium and phosphorus levels are measured.

8. Develop a treatment plan for all participants.

9. Participants are divided into two groups, one group is given oral vitamin D drops 400IU/ d, and the other group do not intervene.

10. The disease activity is re-evaluated at 2, 6, 14, 22, 30, and 38 weeks, and the above serum indexes are re-evaluated.

11. Follow-up for 38 weeks. By comparing the above indicators, observe that in the Han population:

    1. Can Vitamin D drops supplementation increase serum 25 (OH) D levels in patients with CD who are treated with infliximab?
    2. Can Vitamin D drops supplementation improve the condition of patients with CD who are treated with infliximab?
    3. Whether Fok I gene polymorphism affect the efficacy of Vitamin D drops supplementation therapy?
    4. Whether the effects of Vitamin D drops on CD patients who are treated with infliximab is affected by factors such as disease site, disease activity, treatment, etc ..

12. Through statistical analysis, comprehensive analysis of the effectiveness and safety of Vitamin D drops supplementation in Han patients with CD who are treated with infliximab，and its relationship with Fok I gene polymorphism, providing a theoretical basis for further "precise treatment" intervention in inflammatory bowel disease.

Inclusion Criteria:

• Clearly diagnosed patients with CD
• Vitamin D deficiency (<= 20ng / ml)

Exclusion Criteria:

• Pregnancy, lactation
• Liver and kidney insufficiency
• Co-morbid with other autoimmune diseases
• Use antiepileptic drugs or drugs metabolized by liver cytochrome P450 enzymes
• Vitamin D level is normal or high
• Receiving infliximab treatment

Data sets will be made available on relevant requests and in accordance with journal guidelines when publishing results from this study.