The central hypothesis of this proposal is that excess dietary sodium (consumed primarily as salt) is concentrated in the skin as a physiologic response to poor barrier function, and that a low-sodium diet can improve inflammatory skin disease severity. This study is meant to generate pilot data to complement the iDOSE trial (NCT07447063). The study will recruit 50 individuals (10 participants with atopic dermatitis, 10 with psoriasis, and up to 30 'healthy' individuals without skin disease) and measure skin sodium concentration using a non-invasive sodium MRI technique. Healthy individuals will only undergo sodium scans at Visit 1. Participants with atopic dermatitis and psoriasis will be counseled on how to follow the DASH low-sodium diet and asked to maintain the diet for the duration of the 13-week study. After a 1-week wash-in period on the diet alone, they will be asked to add daily sodium chloride tablets in a self-controlled cross-over design. Participants will be randomized in equal groups to either start with sodium tables or placebo tablets. One group will receive sodium tablets for weeks 2-6, no tablets for a washout period during weeks 7-8, then placebo tablets for weeks 9-13. The other group will receive placebo tablets for weeks 2-6, no tablets for a washout period during weeks 6-8 then sodium tablets for weeks 8-13. Sodium consumption will be evaluated using dietary recall questionnaires and urine biomarkers and eczema and psoriasis activity and severity will be measured using validated severity scores and patient-reported outcomes.
