Vitamin D, together with parathyroid hormone (PTH), regulates calcium and phosphate homoeostasis (Brown, Dusso, & Slatopolsky, 1999; Mundy & Guise, 1999) and some (Eskandari et al., 2007; Herran et al., 2000, Hoogendijk et al., 2008; Jorde et al., 2006; May et al., 2010) but not all (Michelson et al., 1996; Schneider et al., 2000) studies have reported higher serum PTH among adults with depression. This evidence concerns the gene PTH and major depressive disorder.