Time to reevaluate the therapeutic use of calcitonin and biological role attributable to parafollicular (C) cells

Abstract There is rich anecdotal evidence that calcitonin significantly increases bone mineral density and reduces fracture risk. However, observation in a previous study of an increased bone formation in calcitonin-deficient mice has led us to reevaluate the therapeutic use of calcitonin and to investigate the primary role of parafollicular (C) cells of the thyroid gland. We found that C cells are involved mainly in the regulation of follicular cell activity in a paracrine manner and in doing so they may regulate the growth rate in newborn by affecting the thyroid hormone levels in the early postnatal period. In the light of reports that showed thyroid physiology is different between populations and it is affected by environmental factors we suggested that C cells may be involved in population differences in thyroid physiology and environmental adaptation. We conclude that C cells may facilitate the adaptation of the follicular cells to environmental changes, enabling more effective coordinated functions of the body and producing variations between populations.