This is your skin on salt: Study suggests atopic dermatitis patients should cut the sodium

Doing something as simple as cutting back on salt can help reduce symptoms of atopic dermatitis (AD).Studies have pointed to possible contributions of diet to AD onset and persistence for decades. But few have focused specifically on the role of salt. And while one previous study showed that eating fast food, which tends to be high in sodium, is associated with a 20% increase likelihood of having AD, and a 70% chance of severe AD among adolescents, specific nutrient or dietary culprits weren’t identified. But, according to a paper in JAMA, more clues arose about sodium having a role in AD came with the introduction of sodium magnetic resonance imaging (MRI). One study using the technology found “that the majority of the body’s exchangeable sodium is stored in the skin and that skin sodium is associated with autoimmune and chronic inflammatory conditions, including AD.”As an aside, the researchers noted that a German textbook from over a century ago recommended a low-salt diet for AD—but overall, there has been little evidence.To investigate sodium further, the researchers, from the University of California in San Francisco, conducted a cross-sectional study of adult participant data from the large, ongoing population study the UK Biobank. One goal was to pull data relating to 24-hour urinary sodium excretion, “which represents approximately 90% of 24-hour dietary sodium intake,” the paper said. The data attained also included body mass index (BMI), age and urine concentrations of potassium, sodium and creatinine. A subset of participants with salt intake lower than recommended amounts was also included. The primary outcome was AD, which was determined from diagnostic and prescription information, with severity taken into account. A subset of participants with active symptoms of AD around the time the urine samples were collected was included in the analyses. Analyses were conducted for a total of 215,832 participants. Of these, 54.3% were female, 45.7% male, 95% were white, and had a mean age of 56.5 years. Their mean 24-hour urine sodium excretion was 3.01 g per day, which works out to an intake of about 1 teaspoon of salt daily. And 23,643 participants (11%) had 2.1 g or less, which was near the recommended amount of sodium intake in the U.K., the paper said. A total of 10,839 (5.0%) participants had AD. Of these, 1,282 (11.8%) of these had active AD within two years of when the urine samples were collected. Those who had AD were more likely to be female and have lower socioeconomic status. Of people with AD, 4,813 (44.4%) had moderate disease, and 320 (3.0%) had severe disease. Those with a 1-g higher 24-hour urine sodium excretion was associated with a greater likelihood of having AD, and active AD.“There were also higher odds of increasing severity of AD associated with higher estimated 24-hour urine sodium excretion,” the paper said. When the researchers looked at participants who had the recommended 2.1 g of 24-hour urinary sodium excretion or less, it was found there was no association with AD. The effect among women was only slightly more than that of men, and there was no apparent effect when race and ethnicity were taken into account. There was no difference by age either.Overall, what was found was that people who had 1-g higher (over the 3.01 g per day average) 24-hour urinary sodium excretion were 11% more likely to have an AD diagnosis, had a 16% higher odds of active AD, and an 11% greater likelihood of more severe AD.“Among participants with less than the NHS-recommended level of sodium intake, there was no evidence for increased AD risk,” the paper said.The researchers noted that while sodium reduction is a cost effective way to help treat hypertension and improve other cardiovascular disease outcomes, “our data support experimental studies of this approach in AD.”The researchers added that a limitation of the study was that it didn’t capture long-term sodium intake. Sodium in the skin can be a marker, or possibly play a role, in other medical and skin conditions, too. One study investigating skin and sodium suggest modern imaging techniques might be able to use skin sodium levels as a marker of certain immune-mediated disease activity or even be a target for therapeutic treatment. In their study in Clinical Experiment Dermatology, researchers conducted a review of studies with a focus on sodium in the skin and disease outcomes.The researchers “found that skin sodium concentration is increased in patients with cardiometabolic conditions including hypertension, diabetes and end-stage renal disease; autoimmune conditions including multiple sclerosis and systemic sclerosis; and dermatological conditions including atopic dermatitis, psoriasis and lipoedema.”Another study from 2022 in the Journal of Investigative Dermatology found that in another skin condition, psoriasis, sodium levels were elevated. Here, in an observational study, the researchers measured skin sodium levels in 37 patients with psoriasis and 19 controls using a sodium MRI (NaMRI). It was found that using the Psoriasis Area Sensitivity Index (PASI), patients whose PASI score was greater than 5 had significantly higher sodium and water content in their skin, but not in other tissues than those with lower PASI or healthy controls.They noted that sodium can accumulate in the skin at concentrations that are higher than serum levels.They also described why sodium in the skin in psoriasis was a compelling area to investigate, and stated that “high sodium environment can lead to pathogenic T helper 17 cell expansion. Psoriasis is a chronic inflammatory skin disease in which IL-17‒producing T helper 17 cells play a crucial role.” They concluded that “Our data describe skin sodium as a pathophysiological feature of psoriasis, which could open new avenues for its treatment.”

This is your skin on salt: Study suggests atopic dermatitis patients should cut the sodium

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