A study - published in the Journal of Investigative Dermatology - suggests that dietary components, and not obesity itself, may lead to skin inflammation and the development of psoriasis. “In our study, we found that short-term exposure to the Western diet is able to induce psoriasis before significant body weight gain,” says Sam T. Hwang, professor and chair of dermatology at UC Davis and senior study author.
The study found that a diet containing high fat and high sugar was required to induce observable skin inflammation. In four weeks, mice on the Western diet had significantly increased ear swelling and visible dermatitis compared to mice fed a controlled diet and those on high fat diet alone. “Eating an unhealthy diet does not affect your waistline alone, but your skin immunity too,” added Zhenrui Shi, visiting assistant researcher in the UC Davis Department of Dermatology and lead author on the study.
The study detailed the mechanisms by which inflammation happens following a Western diet and identified bile acids as key signaling molecules in the regulation of skin immunity. Bile acids are produced in the liver from cholesterol and metabolized in the intestine by the gut microbiota and play an important role in dietary lipid absorption and cholesterol balance in the blood. The study also found that cholestyramine - a drug used to lower cholesterol levels by binding to bile acids in the intestine - helped reduce the risk of skin inflammation and suggests that bile acids mediate the development of psoriasis. The binding of cholestyramine to bile acids in the gut and its subsequent release through the stool allows for lowering of skin inflammation.
Psoriasis causes skin cells to form scales and red patches that are itchy and sometimes painful. Previous studies have shown that obesity is a risk factor for the development or worsening of psoriasis. The Western diet, characterized by a high dietary intake of saturated fats and sucrose and low intake of fiber, has been linked to the increased prevalence of obesity in the world. Further studies are needed to understand the mechanism behind diet-induced skin inflammation and the interaction between metabolism, microbes and immunity.
A Closer Look At An Itchy Skin Condition
An international team led by Johns Hopkins Medicine researchers conducted what is believed to be the largest detailed published study of people with a poorly understood skin condition known as prurigo nodularis (PN). These studies collect information on a whole subset of people at once and at a particular point in time. The results - published by the Journal of the American Academy of Dermatology - provide some of the first published reliable information from a racially diverse population about who likely develops this chronic disease, which is characterized by intensely itchy nodules that develop on the arms and legs that can generalize throughout the body.
The prevalence of prurigo nodularis remains unknown as the condition has been understudied compared with other inflammatory skin diseases, and its origins, causes and treatment are still largely unexplored, however, PN’s impact is significant. “These are patients whose lives have been devastated by an unbearable, persistent itch that dramatically reduces quality of life on par with the most severe diseases treated by our specialty,” says study leader Shawn Kwatra, M.D., assistant professor of dermatology at the Johns Hopkins University School of Medicine.
PN interferes with sleep and affects social interactions with people who may be needlessly afraid of contracting this noninfectious disease. Despite its severe impact, PN has been largely ignored by scientists. To learn more about it, researchers conducted a detailed study of data from 909 adults with PN over a five-year period - 475 females and 434 males. Of the participants, nearly half were African-American, about 42 percent were white, and about three percent were Asian.
The Link Between Various Conditions
The investigators extracted details of the patient group’s comorbidities or other medical problems these patients had at the same time as PN. The majority of patients were between 51 and 65 years old. PN was more prevalent in African-Americans, but not whites, with HIV infection. African-Americans with PN in the patient group were 10.5 times more likely to have HIV than race-matched controls with atopic dermatitis and eight times more likely to have HIV than African-American patients with psoriasis who were treated during this time period.
PN patients were also 2.8, 4.7 and 9.9 times more likely to have diabetes, chronic kidney disease and hepatitis C than patients with atopic dermatitis, respectively. Patients with PN were also nearly three times more likely to have clinical depression compared with patients with atopic dermatitis and 2.4 times more likely to have depression than patients with psoriasis.
The team suggests their information may be used not only in the clinical care of PN patients, but forms a basis for ongoing translational studies to develop novel treatments for the disorder. Kwatra cautions that such associations do not demonstrate that PN causes these disorders or vice versa. More research will be necessary to tease out whether and why these various conditions are linked, which could eventually lead to a better understanding of the mechanism of PN and better targeted treatments.
Knowing the connections between PN and various health conditions could lead physicians to give patients more thorough evaluations to check for other conditions once they’re diagnosed with PN. As PN is associated with dermatologic conditions such as atopic dermatitis in African-Americans, as well as many systemic conditions, further study is needed to determine the exact prevalence.
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With over 30 years of writing and editing experience for newspapers, magazines and corporate communications, Kevin Kerfoot writes about natural health, nutrition, skincare and oral hygiene for Trusted Health Products’ natural health blog and newsletters.
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