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Health Risks from Excessive Calcium

Excessively high levels of calcium in the blood known as hypercalcemia can cause renal insufficiency, vascular and soft tissue calcification, hypercalciuria (high levels of calcium in the urine) and kidney stones [1]. However, hypercalcemia rarely results from dietary or supplemental calcium intake; it is most commonly associated with primary hyperparathyroidism or malignancy [1].

High calcium intake can cause constipation. It might also interfere with the absorption of iron and zinc, though this effect is not well established [1]. High intake of calcium from supplements, but not foods, has been associated with increased risk of kidney stones [1,98,99]. Some evidence links higher calcium intake with increased risk of prostate cancer, but this effect is not well understood, in part because it is challenging to separate the potential effect of dairy products from that of calcium [1].

The Tolerable Upper Intake Levels (ULs) for calcium established by the Food and Nutrition Board are listed in Table 3 in milligrams (mg) per day. Getting too much calcium from foods is rare; excess intakes are more likely to be caused by the use of calcium supplements. NHANES data from 2003–2006 indicate that approximately 5% of women older than 50 years have estimated total calcium intakes (from foods and supplements) that exceed the UL by about 300–365 mg [1,8].

Table 3: Tolerable Upper Intake Levels (ULs) for Calcium [1]
Age Male Female Pregnant Lactating
0–6 months 1,000 mg 1,000 mg
7–12 months 1,500 mg 1,500 mg
1–8 years 2,500 mg 2,500 mg
9–18 years 3,000 mg 3,000 mg 3,000 mg 3,000 mg
19–50 years 2,500 mg 2,500 mg 2,500 mg 2,500 mg
51+ years 2,000 mg 2,000 mg

Interactions with Medications

Calcium supplements have the potential to interact with several types of medications. This section provides a few examples. Individuals taking these medications on a regular basis should discuss their calcium intake with their healthcare providers.

Calcium can decrease absorption of the following drugs when taken together: biphosphonates (to treat osteoporosis), the fluoroquinolone and tetracycline classes of antibiotics, levothyroxine, phenytoin (an anticonvulsant), and tiludronate disodium (to treat Paget’s disease) [121-123].

Thiazide-type diuretics can interact with calcium carbonate and vitamin D supplements, increasing the risks of hypercalcemia and hypercalciuria [122].

Both aluminum- and magnesium-containing antacids increase urinary calcium excretion. Mineral oil and stimulant laxatives decrease calcium absorption. Glucocorticoids, such as prednisone, can cause calcium depletion and eventually osteoporosis when they are used for months [122].

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