The Effect of Vitamin D Supplementation on Psoriasis Severity

The study evaluates the effect of oral vitamin D supplementation on the severity of psoriasis measured by Psoriasis Area Severity Index (PASI) in adults with lower vitamin D levels. Half of the participants will receive vitamin D, while the other half receive placebo.

Studies have indicated an association between lower levels of vitamin D and increased risk of psoriasis. This study investigate if vitamin D supplementation can reduce the severity of the skin disease as measured by Psoriasis Area Severity Index (PASI), as well as positively influence the cardiometabolic profile and skin microbiota of persons with psoriasis through a winter season.

Consenting participants will be randomized to high dose vitamin D (20.000 IU/week) versus placebo for four months. The participants will be recruited based on their 25-hydroxyvitamin D (25(OH)D)-measurements in the 7th survey in the Tromsø study where 21.083 subjects attended.

In order to assure sufficient study participation we will (in season 2, winter 2018/19) include 20-40 persons from the general population in Tromsø aged 20-79, who did not partake in Tromsø 7, through advertisement and contact with patient organizations.

Eligibility Criteria:
Inclusion Criteria:

* Plaque psoriasis diagnosis confirmed by a dermatologist at visit 1.
* Psoriasis Area Severity Index (PASI) score \> 0 at inclusion.
* Serum 25 hydroxyvitamin D levels \< 60 nmol/L confirmed at visit 1
* Do not meet exclusion criteria

Exclusion Criteria:

* age above 79 years
* subjects allergic to nuts (the study capsules contain peanut oil)
* subjects with primary hyperparathyroidism
* granulomatous diseases (sarcoidosis, tuberculosis, granulomatosis with polyangiitis (Wegners))
* reduced kidney function (creatinine \> 130 μmol/L in males and 120 μmol/L in females)
* measured systolic blood pressure (BP) \> 174 mmHg, diastolic BP \> 104 mmHg
* poorly controlled diabetes (HbA1c \> 9.0 %)
* renal stones the last five years
* subjects who use solarium on a regular basis (more than twice a month on average), nor can this be performed under the course of the study
* subjects who plan holiday(s) in tropical areas including the Canary Islands for more than two weeks under the course of the study
* subjects with clinical signs of proximal myopathy (problems with standing up from chair or walking stairs)
* subjects seriously physically or mentally ill and unfit for participation in a clinical study (as judged by one of the study doctors)
* subjects who have been diagnosed with or treated for organ cancer within the past 12 months (basal cell carcinoma and other limited nonmelanoma skin cancer or melanoma in situ can be included).
* pregnancy. Females of child bearing potential (below the age of 50) may participate if they use highly effective anticonception (hormonal, intrauterine device(IUD), in accordance with Clinical Trial Facilitation Group(CTFG) guidelines); if living in a relation with a partner who has been sterilized; if living in a lesbian relationship; or do not have or wish to have a male partner. If, in spite of the above, a pregnancy occurs during the study, it will lead to exclusion form the study. In females \< 50 years a pregnancy test will be performed at inclusion
* subjects using vitamin D supplementation (incl. cod liver oil) above 800 IU (20 microgram) (5 ml codliver oil = 400 IU) or active vitamin D drugs (Rocaltrol or Etalpha) within the last month before study start are excluded. Furthermore, vitamin D supplements (e.g. codliver oil) or drugs apart from the study medication can not be used during the course of the study.
* subjects who during the last month before inclusion have used phototherapy/light therapy or heliotherapy as prescribed by a dermatologist, nor can this treatment be performed under the course of the study
* subjects who have started treatment with a new oral or injection drug for psoriasis or psoriasis arthritis (E.g. Methotrexate, Cyclosporine, Acitretin or biological treatment like Humira, Remicade, Stelara and others ) within the last 2 months (evaluated by dermatologist). Nor can a new oral or injection drug which influences psoriasis severity be introduced during the study. In this case the participant will be withdrawn from the study.
* subjects who have participated (been randomized) in the pilot study
* In season 1: subjects who have participated (been randomized) in the D-COR study.

Topical treatments containing vitamin D or vitamin D analogs (including Daivobet) cannot be used during the study. If a subject uses these products regularly, replacement products which only contain local steroids will be prescribed as alternates or the participant is excluded.