Eczema may sometimes be caused by eating too much salt

Eating too much salt has been linked to eczema after researchers found people with the skin condition have elevated levels of sodium in their urine. 

More than 200 million people worldwide have eczema, which causes dry, cracked and itchy skin. Common triggers include irritants found in soaps and detergents, as well as environmental or food allergens. Previous research has also linked frequent fast food consumption to an increased risk of severe eczema in children. 

To see if salt may play a role, Katrina Abuabara at the University of California, San Francisco (UCSF), and her colleagues examined urine sample data from more than 215,800 adults in the UK Biobank study, of whom more than 10,800 had eczema.

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The researchers used a urine sample from each participant to estimate their urinary sodium excretion over 24 hours. About 90 per cent of dietary sodium is later excreted in urine, making the waste product a relatively reliable way of gauging someone’s salt consumption.

Overall, the study participants excreted an estimated 3.01 grams of sodium in their urine over 24 hours, on average. The recommended sodium intake for adults is typically around 2.5 grams per day, equivalent to 6 grams, or one teaspoon, of salt. 

The researchers found that for every additional gram of sodium that the participants excreted, their odds of having been diagnosed with eczema rose by 11 per cent. Their risk of having eczema at that time also increased by 16 per cent.

The team acknowledges that a single urine sample may not accurately reflect a person’s typical salt intake. But in another part of their study, the researchers surveyed a separate group of more than 13,000 adults in the US about their daily diet, finding further correlations between a high salt intake and eczema. 

Previous research has shown that sodium can activate cells in the immune system, triggering some inflammatory pathways, says Abuabara. People with eczema have an overly active immune response to allergens or irritants, which causes skin inflammation and subsequent symptoms.

Although the study shows an association between high urinary sodium levels and eczema, further work is needed to establish that the former causes the latter, says team member Brenda Chiang, also at UCSF.

It is too early to say that lowering dietary sodium levels can reduce eczema severity or the risk of developing it in the first place, says Carsten Flohr at King’s College London.

Abuabara says her team will soon start enrolling people to take part in a study funded by the US National Institutes of Health looking at the relationship between dietary sodium, levels of sodium on the skin and eczema severity.