Skin production of vitamin D from exposure to the sun improves the condition of psoriasis — an autoimmune skin disease that consists of red, scaly patches that have a silvery-white appearance. This is using vitamin D as therapy, not for prevention; however, there’s no evidence that you can take large amounts of vitamin D as a pill and get the same benefits as UV light or a topical form of vitamin D.
Diagnosing and treating psoriasis
Psoriasis usually begins between the ages of 15 and 25, but it can occur at any age. Psoriatic patches occur on the elbows, knees, scalp, genitals, palms of the hands, and soles of the feet. Some people have more extensive disease that covers the entire body. The patches itch and can be painful.
The psoriatic patches make up 90 percent of cases, but another, pustular form consists of raised bumps that contain pus but no bacteria. In the nonpustular form, the patches of disease, called psoriatic plaques, tend to occur where the skin is scratched or otherwise injured.
Psoriasis tends to improve and then recur irregularly, making it difficult to know whether treatment is helping. The condition is graded as:
Mild if it affects less than 3 percent of the body
Moderate if it affects 3 to 10 percent of the body
Severe if it affects more than 10 percent of the body
The cause is unclear, but psoriasis seems to have immune characteristics because T cells and cytokines are involved in addition to local skin characteristics. Skin cells grow and divide without control. Hereditary factors also are at work: Psoriasis is more common in certain families and when certain genetic markers are present.
Psoriasis may be associated with depression and diminished quality of life. It’s not contagious.
About 15 percent of patients also have psoriatic arthritis, which consists of joint pain, stiffness, and swelling. It comes and goes like the skin condition and is usually mild, but it may be progressive and cause deformities. Psoriatic arthritis is most common in the fingers and toes.
Many treatments for psoriasis exist, but nothing eliminates the disease permanently. Among the treatments are the following:
Drugs that reduce T cells
Drugs that eliminate cytokines
Topical treatment with creams containing steroids
Phototherapy, exposure to ultraviolet irradiation
Immunosuppressive drugs with names like methotrexate and cyclosporine
Oral steroid drugs, like dexamethadone
Antihistamines, to reduce itching
People who have psoriasis are stuck with it for life. Most people just experience outbreaks of localized patches on the elbows and knees.
Vitamin D levels and psoriasis
Vitamin D has a definite role in treating psoriasis. Because the condition involves a component of adaptive immunity (the T cells), the function of vitamin D in reducing adaptive immunity plays a role. Vitamin D has the ability to reduce cell proliferation in cancers; this action may reduce the increased production of skin cells.
Vitamin D is linked to the treatment of psoriasis in the following ways:
Exposure to the sun and the skin’s production of vitamin D decreases the severity and duration of a psoriatic outbreak.
Sunlight (heliotherapy) kills the activated T cells in the skin. Skin turnover is reduced, and the scaling and inflammation subside. Patients need only brief exposure — just minutes a day. Prolonged exposure can make the symptoms worse and damage the skin.
Various types of UVB phototherapy (broadband, narrowband excimer laser) use controlled doses of UVB light from an artificial light source. It’s used on patches of psoriasis and on psoriasis that doesn’t respond to topical treatment. The duration of treatment must be carefully monitored to avoid burns, because this is a more powerful UVB light.
UVB light therapy can be combined with topicals to make the skin more sensitive to the effect of the light.
Synthetic forms of active vitamin D, like calcipotriene or tacalcitol in topical preparations, can be used to treat mild or moderate psoriasis. It works by slowing the growth of skin cells and reducing local inflammation. Also these vitamin D drugs help make other topical treatments, like corticosteroids, more effective.
Any kind of light therapy works just like using sunlight. You must avoid excessive exposure and burning, especially in psoriasis, because excess exposure can make the disease worse. Also, taking oral vitamin D hasn’t been shown to work. The problem may be that vitamin D formed in the skin through sun exposure can lead to high levels of calcitriol that act locally to improve the psoriasis, whereas when you take vitamin D by mouth there’s no mechanism in place to tell your body to make higher levels of calcitriol just in the skin.