It is plausible that this adverse association between depression and poor bone health may result from low 25(OH)D concentrations since low 25(OH)D can trigger a compensatory rise in levels of parathyroid hormone (PTH) [36], which not only promotes the conversion of 25(OH)D to its active form, calcitriol, but also increases bone resorption [37]. The gene discussed is PTH; the disease is major depressive disorder.