The purpose of this study is to determine whether supplementation with oral vitamin D (cholecalciferol) improves metabolic parameters in patients with moderate to severe psoriasis.

Inclusion Criteria:

• Clinical diagnosis of moderate to severe psoriasis.
• Being treated with methotrexate with stable doses for al least 1 month.

Exclusion Criteria:

• Phototherapy within the past 2 months.
• History of psoriatic arthritis, rheumatoid arthritis, type 1 diabetes mellitus or inflammatory bowel disease.
• Use of vitamin d supplements or fish oil supplements in the past 2 months.
• Use of hypolipidemic drugs, hypoglycemic drugs, glucose sensitizers, oral corticosteroids, orlistat, cholestyramine, phenobarbital or phenytoin within the past 2 months.
• Pregnancy or lactation.