From the Manufacturer:
Although calcium plays at least some minor role in lowering blood pressure, the mechanisms involved appear complex and somewhat unclear. The level of calcium in the blood is tightly regulated by parathyroid hormone (PTH), and low intake of calcium causes elevations in PTH, which in turn have been implicated in the development of hypertension. High calcium intake has also been associated with a reduced risk of cardiovascular disease in postmenopausal women.