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A higher level of daily sodium intake was associated with an increased risk of atopic dermatitis, a cross-sectional study suggested.

In a cohort of over 215,000 adults from the U.K. Biobank, multivariable logistic regression showed that a 1-g increase in estimated 24-hour urine sodium excretion was associated with increased odds of atopic dermatitis (adjusted OR 1.11, 95% CI 1.07-1.14), active disease (aOR 1.16, 95% CI 1.05-1.28), and increasing disease severity (aOR 1.11, 95% CI 1.07-1.15), reported Katrina Abuabara, MD, MSCE, of the University of California San Francisco, and colleagues.

In a validation cohort of 13,014 participants from the National Health and Nutrition Examination Survey, a 1-g increase in dietary sodium intake per day, which was estimated using dietary recall questionnaires, was associated with a higher risk of current atopic dermatitis (aOR 1.22, 95% CI 1.01-1.47), they noted in .

The observed mean 24-hour urinary sodium excretion of 3.01 g per day represents a higher level of sodium intake than the National Health Service-recommended maximum of 6 g or approximately 1 tsp of salt per day (i.e., 2.3 g of sodium), Abuabara and team explained. In a model of participants who had the recommended 2.1 g of 24-hour urinary sodium excretion or less, there was no association with atopic dermatitis (aOR 0.88, 95% CI 0.70-1.11).

These population-level findings were in line with other data linking higher levels of dietary sodium intake with atopic dermatitis, the authors observed, adding that "excessive dietary sodium, common in fast food, may be associated with AD [atopic dermatitis]." Indeed, "sodium magnetic resonance imaging 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."

A previous found that the amount of lesional skin sodium was 30 times greater among patients with atopic dermatitis compared with healthy controls.

In a sensitivity analysis additionally adjusting for self-reported blood pressure medication use, higher estimated 24-hour urine sodium excretion was associated with higher odds of atopic dermatitis (aOR 1.09, 95% CI 1.06-1.13) and higher odds of active atopic dermatitis (aOR 1.15, 95% CI 1.04-1.27). When body mass index was considered, the authors noted an association between higher estimated 24-hour urine sodium excretion and increased odds of atopic dermatitis (aOR 1.08, 95% CI 1.03-1.13), although the association with active atopic dermatitis was not significant (aOR 1.03, 95% CI 0.91-1.17).

"Excessive sodium consumption may play a role in the observed between AD and hypertension," Abuabara and colleagues wrote. "Atopic dermatitis is associated with a 10% to 20% increased risk of cardiovascular disease outcomes, and a strong dose-response association with AD activity and severity has been found."

Interpretation of the findings is limited by the study's use of one single urine sample, Deirdre Hooper, MD, co-founder of Audubon Dermatology in New Orleans, told MedPage Today, which the authors also acknowledged "only captures dietary intake of the last 24 hours and is not the best measure of usual or long-term intake of sodium."

In addition, "we don't know if it's the chicken or the egg -- is it something in the way you metabolize sodium or how much sodium you eat," Hooper said. "If you consider sodium as a possible inflammatory part of your diet and your atopic dermatitis is flaring, you can look at your diet and ask what you've been eating lately. Given that high-sodium diets are linked to cardiovascular disease, trying a low-sodium diet is certainly not a bad thing."

The authors concluded that "identifying specific modifiable exposures is a high priority for patients and their caregivers, who cite the unpredictability of the disease course as a major contributor to the burden of disease. These findings suggest that restriction of dietary sodium intake may be a cost-effective and low-risk intervention for AD."

For this study, Abuabara and team used data on 215,832 participants ages 37 to 73 from the U.K. Biobank to estimate 24-hour urinary sodium excretion based on urine biomarkers collected at a single time point. Mean age was 56.5 years, 54.3% were women, and 95.2% were white.

Overall, 5% had a diagnosis of atopic dermatitis, including 11.8% with active disease, within 2 years of the time of urine collection.

The researchers adjusted for age, sex, race and ethnicity, Townsend Deprivation Index, and education to measure the association between estimated 24-hour urinary sodium excretion, which represents approximately 90% of 24-hour dietary sodium intake, and atopic dermatitis.

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