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A study found a link between vitamin D levels and the severity of psoriasis. Raymond Forbes LLC/Stocksy
  • Psoriasis is an autoimmune skin disorder characterized by raised, inflamed and scaly patches of skin that can also be itchy and painful.
  • The severity of psoriasis varies greatly from person to person.
  • New research shows that low vitamin D levels may be associated with more severe psoriasis.

Psoriasis is a condition that affects more than 7.5 million people in the United States. New research from Warren Alpert Medical School of Brown University suggests that low vitamin D levels may be associated with more severe psoriasis.

The exact cause of psoriasis is not fully understood, but scientists believe that it is an autoimmune condition, which means that it is the result of the immune system accidentally attacking your body instead of protecting it. In psoriasis, this autoimmune activity causes new skin cells to be produced much faster than normal, and these skin cells accumulate on the skin’s surface in the form of thick, scaly patches.

Symptoms of psoriasis can range from mild to severe. According to the National Psoriasis Foundation:

  • mild psoriasis affects less than 3% of the body
  • moderate psoriasis affects 3–10% of the body
  • severe psoriasis affects more than 10% of the body

Rachel K. Lim, an MD candidate at the Warren Alpert Medical School of Brown University, presented the new study’s findings at NUTRITION 2023, the annual flagship meeting of the American Society for Nutrition held July 22-25 in Boston.

Medical News Today asked Eunyoung Cho, ScD, research team leader and associate professor of dermatology and epidemiology at Brown University, to explain the biological connection between vitamin D and psoriasis.

“Keratinocytes, which are cells in your skin, have vitamin D receptors. Currently, topical vitamin D analogs, which mimic the effects of vitamin D, are used to treat psoriasis because these analogs bind to vitamin D receptors on keratinocytes to prevent their proliferation. This proliferation is what leads to the thick plaques characteristic of psoriasis.”

– Dr. Eunyoung Cho

Studies conducted in several countries, including Italy, Brazil, and Nepal, have shown that serum levels of vitamin D are significantly lower in people with psoriasis and correlate with the severity of the disease.

Since most previous studies have been conducted outside of the US, Dr. Cho and her collaborators sought to investigate whether this relationship would be replicated in a large, nationally representative US population.

Dr. Cho’s team used data from the National Health and Nutrition Examination Survey (NHANES) to identify psoriasis cases between 2003 and 2006 and between 2011 and 2014. They found 491 cases from the 40,401 participants screened, with 162 cases from 2003-2006 and 329 from 2011-2014.

They also collected information about the levels of vitamin D in the blood, psoriasis-affected body surface area (a measure of the extent of psoriasis on the body), and other factors like age, gender, race, body mass index, and smoking habits.

To assess the relationship between low vitamin D levels and the severity of psoriasis, they used a mathematical method called “multivariate linear regression.”

They found that as the levels of vitamin D in the blood decreased, the severity of psoriasis increased. People with the least psoriasis-affected body surface area had the highest mean serum vitamin D levels (67 nmol/L), while those with the greatest psoriasis-affected body surface area had the lowest mean serum vitamin D levels (56 nmol/L).

The researchers saw a similar trend when they divided people into groups based on psoriasis-affected body surface area and looked at the percentage of people with vitamin D deficiency in each group. 39% of the group with the most severe psoriasis were deficient in vitamin D compared to 25% of the group with the least severe psoriasis.

“Only one previous study, published in 2013, has used NHANES data to analyze the relationship between vitamin D and psoriasis,” Lim was quoted as saying in a press release. “We were able to add more recent data, which more than tripled the number of psoriasis cases analyzed, making our results more up-to-date and statistically powerful than previously available data.”

Dr. Tina Bhutani, associate professor of dermatology, co-director of the Psoriasis and Skin Treatment Center, and director of the Dermatology Clinical Research Unit at the University of California, San Francisco, pointed out that these findings are not novel since “similar associations have been reported in the past.”

However, “the advantage of NHANES is that it is likely to be more representative of the US population vs other previous studies given the specialized sampling used by this survey,” Dr. Bhutani told MNT.

Dr. Joel M. Gelfand, James J Leyden professor of dermatology and of epidemiology at the University of Pennsylvania Perelman School of Medicine, commented that the study “shows a modest association between vitamin D levels and psoriasis severity” but warned that it cannot be used to establish a causal relationship.

Based on this study, “we cannot determine if more severe psoriasis leads to slightly lower vitamin D levels or [if] slightly lower Vitamin D levels lead to more severe psoriasis,” Dr. Gelfand said.

Dr. Cho noted that “while topical vitamin D analogs are already used to treat psoriasis, further research, such as large randomized clinical trials of oral vitamin D supplementation, is warranted before any firm medical recommendations are made on oral vitamin D supplementation use among psoriasis patients.”

Nonetheless, people with psoriasis who also have vitamin D deficiency should “discuss this with their clinicians and treat the deficiency,” Dr. Cho recommended.

Dr. Bhutani agreed that despite the association between vitamin D levels and psoriasis severity shown by these findings: “We do not have enough information here to recommend the use of vitamin D supplementation in our psoriasis patients.”

In the same vein, Dr. Gelfand told MNT that “the current level and quality of evidence is insufficient to recommend monitoring or supplementing levels of vitamin D in patients with psoriasis for the goal of preventing or treating psoriatic disease.”

In their comments to MNT, Dr. Bhutani and Dr. Gelfand both mentioned that previous studies have tested the use of vitamin D supplementation in psoriasis and produced mixed results.

A clinical trial published in 2022 “showed some evidence that vitamin D supplementation may slightly prevent the development of autoimmune diseases, with some evidence, albeit not statistically significant, that this includes prevention of psoriasis,” said Dr. Gelfand.

However, a clinical trial published in 2023 showed that vitamin D supplementation did not affect psoriasis severity.

“A cautionary tale is the experience of vitamin D and prevention of cancer and cardiovascular disease – after many years of intense investigation, large RCTs involving >25,000 patients showed no benefit of Vitamin D supplementation for preventing these major health outcomes,” Dr. Gelfand observed.