An elevated serum calcium level may be associated with disorders of the parathyroid glands, small bean-shaped pieces of tissue embedded in the thyroid gland. One-third of individuals with hyper-parathyroidism may exhibit hypertension because the parathyroid gland is secreting more parathyroid hormone than normal.

Parathyroid hormone has direct effects on both the intestine and the bones. It causes the intestine to absorb more calcium from the diet and it causes bone to mobilize or release calcium to the blood. Increased calcium in the blood causes changes in the kidneys, ranging from calcium deposits to formation of kidney stones.

Damaged kidneys may respond by producing substances that increase the blood pressure, such as angiotensin. In addition, excess calcium itself can cause high blood pressure by directly causing blood vessels to constrict. In some cases, treating the elevated calcium level alone fixes the high blood pressure without the addition of specific anti-hypertensive medications.