Too much calcium in your blood, a condition called hypercalcemia, can affect nearly every system in your body. Normal blood calcium falls between 8.5 and 10.2 milligrams per deciliter. When levels climb above that range, you may experience symptoms ranging from mild fatigue and constipation to serious complications like kidney stones, weakened bones, and irregular heartbeats.
Early Signs You Might Notice
Mild excess calcium often produces vague symptoms that are easy to brush off. You might feel unusually thirsty, need to urinate more often than normal, or notice persistent constipation. Fatigue, brain fog, and a general sense of feeling “off” are common early complaints. Nausea, loss of appetite, and stomach discomfort round out the picture. Doctors have a classic shorthand for the full range of symptoms: “bones, stones, groans, and moans,” referring to bone pain, kidney stones, abdominal complaints, and neurological symptoms like confusion or depression.
As calcium levels rise higher, symptoms become harder to ignore. Muscle weakness, twitching, and even heart palpitations can develop. Severe hypercalcemia (above 14 mg/dL) is a medical emergency that can cause confusion, extreme drowsiness, and dangerous heart rhythm changes.
What Causes Calcium to Build Up
The most common cause is overactive parathyroid glands, four tiny glands in your neck that regulate calcium. Usually a small, noncancerous growth on one of these glands causes it to pump out too much parathyroid hormone, which pulls calcium from your bones into your bloodstream. This accounts for the majority of cases found during routine blood work.
Cancer is the second most common cause. Lung cancer, breast cancer, and cancers that have spread to bone can all drive calcium levels up, sometimes dramatically. Certain cancers release proteins that mimic parathyroid hormone, tricking the body into flooding the blood with calcium.
Other causes include:
- Too much vitamin D, which increases calcium absorption from food
- Dehydration, which concentrates calcium in a smaller volume of blood
- Medications like lithium and thiazide diuretics (water pills), both of which can raise parathyroid hormone levels
- Prolonged bed rest, especially in children, which causes bones to release calcium
- Chronic kidney disease, which disrupts the body’s normal calcium regulation
- Granulomatous diseases like sarcoidosis and tuberculosis
When Supplements Are the Problem
Taking too much calcium or vitamin D in supplement form over time can push blood levels into dangerous territory. The NIH sets the tolerable upper intake level for calcium at 2,500 mg per day for adults aged 19 to 50, dropping to 2,000 mg per day for adults over 50. These limits include calcium from both food and supplements combined.
For reference, the recommended daily amount for most adults is 1,000 mg (1,200 mg for women over 50 and anyone over 70). If you’re already eating dairy, leafy greens, and fortified foods, a large supplement on top can easily push you past the upper limit.
A specific condition called milk-alkali syndrome can develop when people take large amounts of calcium carbonate, the form found in many antacids and common supplements. Intakes above 2 grams of elemental calcium per day with absorbable alkali have triggered the syndrome, and doses of 2.5 to 3 grams per day of calcium carbonate reliably produce it. What happens is a vicious cycle: the excess calcium suppresses parathyroid hormone, the kidneys start retaining bicarbonate, and the resulting alkaline blood chemistry causes the kidneys to reabsorb even more calcium instead of flushing it out. Dehydration from increased urination makes everything worse. As long as the person keeps taking the supplements, the cycle continues.
Long-Term Damage to Bones and Kidneys
Paradoxically, too much calcium in your blood often means too little calcium in your bones. When the parathyroid glands are overactive, they continuously signal bones to release their calcium stores. Over months and years, this leads to osteoporosis, leaving bones thin and fragile. People with chronic hypercalcemia face a genuinely higher fracture risk, even though their blood is saturated with the very mineral bones need.
The kidneys take a beating too. When they filter excess calcium, crystals can form and gradually combine into kidney stones. These stones cause intense flank pain and can block urine flow. Beyond stones, persistently high calcium forces the kidneys to work overtime concentrating urine, which can eventually impair kidney function. Left untreated long enough, this can progress to chronic kidney damage.
The heart is also vulnerable. Calcium plays a central role in the electrical signals that keep your heart beating in rhythm. Excess calcium can shorten and alter those signals, potentially triggering arrhythmias. In severe cases, this is what makes very high calcium levels life-threatening.
How High Calcium Is Diagnosed
Hypercalcemia is typically caught through a routine blood test that measures total calcium. If that result comes back elevated, your doctor will often check a few additional things. Total calcium in your blood is partly bound to a protein called albumin, so if your albumin levels are abnormal (common in hospitalized or chronically ill patients), the total calcium number can be misleading. A corrected calcium formula adjusts for this, though it’s imperfect in certain populations like people with kidney disease or those in intensive care.
The most accurate measurement is ionized calcium, which looks only at the “free” calcium actually active in your body. Once high calcium is confirmed, blood tests for parathyroid hormone, vitamin D levels, and kidney function help pinpoint the underlying cause.
How It’s Treated
Treatment depends on the severity and the cause. For mild cases discovered incidentally on blood work, especially from overactive parathyroid glands, the approach may simply involve monitoring, staying well hydrated, and avoiding excessive calcium or vitamin D supplementation.
When calcium levels are significantly elevated, the first step is aggressive hydration with IV fluids to help the kidneys flush out excess calcium. For moderate to severe cases, medications that slow the release of calcium from bones are used. These work over the course of several days to two weeks, bringing levels back down gradually. In cases caused by a parathyroid growth, surgery to remove the overactive gland is often curative.
If supplements or antacids are the culprit, simply stopping them usually resolves the problem, though kidney function and calcium levels need monitoring during recovery. For cancer-related hypercalcemia, treating the underlying cancer is the primary goal, with calcium-lowering therapies used to manage symptoms in the meantime.
Practical Steps to Protect Yourself
If you take calcium supplements, check whether you actually need them. Many people get enough calcium through food alone, and unnecessary supplementation is one of the most preventable causes of elevated calcium. Keep your total daily intake from all sources below 2,000 to 2,500 mg depending on your age. Be especially careful combining calcium supplements with vitamin D supplements, antacids containing calcium carbonate, or fortified foods and beverages.
Stay well hydrated, particularly if you take any medications known to raise calcium levels. And if you develop a combination of increased thirst, frequent urination, constipation, and fatigue that doesn’t have an obvious explanation, a simple blood test can check your calcium level and either rule out or catch the problem early, before it has a chance to damage your bones or kidneys.