PTH and major depressive disorder: Compared to 1087 control individuals, calcidiol levels were 14% lower in 169 persons with minor depression, whereas their PTH was 5% higher. Twenty-six persons with MDD also had a lower calcidiol level by 14% and higher PTH by 33%. Decreased serum calcidiol levels and increased serum PTH levels were significantly associated with depression severity (Center for Epidemiologic Studies Depression Scale).