In 2011, Dr. Peroi et al. published a paper in British Journal of Dermatology * discovered that the lower the vitamin D level, the worse the eczema is for children.
You might have heard of phototherapy for treating eczema patient. The idea is to use narrow band UVB to increase calcitrol (vitamin D3) level. The effects could result local immunosuppression and direct anti-itch effects. In invitro studies, vitamin D3 (calcitriol) has been shown to induce cathelicidin expression in keratinocytes, that enhances antimicrobial activity against S. aureus. While getting such therapy requires serious commitment (multiple visits at dermatologist office) and deal with certain side effects, vitamin D could potentially be obtained through alternative sources other than light or sun array. For instance, fortified food (cereals and juice) or vitamin D supplement (there are ones that are designed for children, the one we recommend is L’il Critters Vitamin D Gummy Bears. You can get them from Amazon or local stores).
Foods rich in vitamin D include, fatty fish such as salmon, cheese, egg yolks, and certain mushrooms. If yourself or your child has any allergic reactions to fish, dairy products or eggs, then vitamin D supplement, fortified cereal, combined with moderate sun exposure are some good options.
* D.G. Peroni, G.L. Piacentini, E. Cametti, I. Chinellato, A.L. Boner
The British Journal of Dermatology. 2011;164(5):1078-1082.