Parathyroid Hormone: What It Does, Why It Matters, and How It Affects Your Bones and Blood

When your body needs more calcium, it turns to the parathyroid hormone, a key regulator of calcium and phosphate levels in the blood, produced by four tiny glands behind the thyroid. Also known as PTH, it’s the main reason your bones don’t crumble and your nerves don’t misfire. Without it, your muscles would twitch, your heart could skip, and your bones would slowly weaken.

These four small glands don’t make much hormone—but what they do make matters a lot. If they overproduce, you get hyperparathyroidism, a condition where too much PTH pulls calcium out of your bones and floods your bloodstream. That’s when you might start losing bone density, forming kidney stones, or feeling constantly tired. On the flip side, if they underproduce—hypoparathyroidism, a rare disorder where PTH levels drop too low, causing calcium to fall dangerously.—you could get numb fingers, muscle cramps, or even seizures. Most people don’t realize how tightly your blood calcium is controlled, and how much of that control comes from these tiny glands.

Doctors check PTH levels when your calcium is off—not just to see if it’s high or low, but to figure out why. Is your kidney failing? Are you vitamin D deficient? Is there a benign tumor on one of the parathyroid glands? The answer isn’t always obvious, which is why testing PTH alongside calcium and vitamin D gives the full picture. Even if you’ve never heard of PTH, it’s working behind the scenes every single day to keep your body running smoothly.

What you’ll find below are real-world stories and science-backed explanations about how parathyroid hormone affects everyday health—from medication interactions that mess with calcium balance, to how supplements like magnesium can interfere with bone drugs, and why some people end up with strange symptoms after thyroid surgery. These aren’t abstract concepts. They’re the kinds of things people live with, and then finally understand after years of confusion.