PTH and hyperparathyroidism: Elevated PTH is associated with poor outcome in HF patients [56]; our findings demonstrate that vitamin D3 supplementation can markedly improve PTH concentrations at higher circulating levels of 25(OH)D, further substantiating the existing data showing that higher circulating 25(OH)D concentrations help mitigate hyperparathyroidism. Vitamin D status is closely related to PTH status and 25(OH)D appears to suppress PTH across at all levels of 25(OH)D status [57].