A 1000 IU dose of vitamin D2 daily was as effective as 1000 IU vitamin D3 in maintaining serum 25-hydroxyvitamin D levels and did not negatively influence serum 25-hydroxyvitamin D3 levels. Therefore, vitamin D2 is equally as effective as vitamin D3 in maintaining 25-hydroxyvitamin D status.

We hypothesize that keratinocytes express Dio3 in vivo to maintain cutaneous health and prevent the skin from becoming hyperproliferative. Our data support the developing recognition that the primary role of thyroid hormone deiodinases in some tissues may be the degradation of thyroid hormone to protect the tissue against thyrotoxicosis.

4.