TPO and Hashimoto thyroiditis: Vitamin D deficiency is highly prevalent in endocrine disorders and its supplementation appears to have beneficial effects, as described in one of the recent reviews by Galușca et al. In an analysis of the literature on Hashimoto’s disease, low vitamin D production appeared to be associated with higher anti-thyroid peroxidase (anti-TPO) antibody titers and thyroid volume, while supplementation was addressed in connection with a reduction in antibodies levels in some studies.