The purpose of this study is to treat persistent MRSA carriers with vitamin D supplementation during a 12 month to see if the number of MRSA positive patients can be reduced.

Inclusion Criteria:

1. Persistent MRSA-carriers as defined as 2 MRSA-positive bacterial cultures from at least one location, at least 3 months apart and during 3 years prior to inclusion.
2. Men and women aged ≥18-75
3. Signed 'informed consent'
4. Negative pregnancy test (U-hcg) and have to accept the use of adequate anti-conceptive method (contraceptives, hormone/copper-spiral).

Exclusion Criteria:

1. Should not be on vitamin D supplementation at least 6 months prior to inclusion.
2. Serum level of 25-hydroxy vitamin D3 >75 nmol/L
3. Ongoing and continuous antibiotic treatment. The patient should be off antibiotics at least 30 days prior to inclusion
4. Known sarcoidosis
5. Primary or secondary hyperparathyroidism
6. Kidney failure as defined as a normal age-adjusted creatinin.
7. Long term systemic treatment with corticosteroids or other immunosuppressive medication
8. Taking thiazides
9. Hypercalcaemia (verified by a laboratory result younger than 2 month)
10. Ongoing malignancy disorder
11. If plans to leave the Stockholm county within 12 months of inclusion
12. History of kidney stones
13. Pregnancy (ongoing or planned)
14. Breastfeeding women
15. Taking part of another clinical study involving drugs
16. Hypersensitivity to cholecalciferol and/or any of the excipients
17. Other criteria that could jeopardize the study or its intention as judged by the investigator