Background

Calcium is an essential nutrient found in many foods, such as dairy products, canned sardines and salmon (with bones), and leafy greens. The bones and teeth contain over 99% of all calcium in the human body.

Bones are always breaking down and rebuilding. Calcium is needed for this process, but the concentration of calcium in the body tends to decline with age. Taking extra calcium helps the bones rebuild and stay strong. The heart, nerves, and blood-clotting systems also need calcium.

People commonly take calcium by mouth for the treatment and prevention of low calcium levels in the blood, osteoporosis, softening of the bones, and PMS. It is also used for cancer, stroke, and many other conditions, but there is no good scientific evidence to support many of these other uses.

In the US and Canada, foods that contain calcium and vitamin D are allowed to say on the label that they might reduce the risk of osteoporosis.

Safety Safety definitions

When taken by mouth: Calcium is likely safe when used in recommended amounts of about 1000-1200 mg daily. Calcium can cause some minor side effects such as belching or gas. But calcium is possibly unsafe when taken in doses above the daily tolerable upper intake level (UL). The UL is 2500 mg for adults ages 19-50 years and 2000 mg for adults over 50 years. Taking more than this daily can increase the chance of having serious side effects.

Special Precautions & Warnings:

Pregnancy and breast-feeding: Calcium is likely safe when taken by mouth in recommended amounts. But calcium is possibly unsafe when taken by mouth in doses above the daily tolerable upper intake level (UL). The UL is 3000 mg for those under 18 years of age and 2500 mg for those over 18 years of age. Higher doses might increase the risk of seizures in the infant. Be sure to consider total calcium intake from both dietary and supplemental sources of calcium. Avoid taking more than 1000-1200 mg of calcium from supplements daily unless prescribed by your doctor.

Children: Calcium is likely safe when taken by mouth in recommended amounts. But calcium is possibly unsafe when taken by mouth in doses above the daily tolerable upper intake level (UL). The UL is 1000 mg for those 0-6 months old, 1500 mg for those 6-12 months old, 2500 mg for those 1-8 years old, and 3000 mg for those 9-18 years old. Children should consume enough calcium to meet daily requirements, but should not consume extra calcium.

Low acid levels in the stomach (achlorhydria): People with low levels of gastric acid absorb less calcium if calcium is taken on an empty stomach. People with low acid levels should take calcium supplements with meals.

Too much calcium in the blood (as in parathyroid gland disorders and sarcoidosis): Calcium should be avoided if you have a condition that causes high calcium levels. Taking calcium supplements can cause calcium levels to increase even more.

Kidney disorders: In people with kidney disorders, taking calcium supplements can increase calcium levels too much. Speak with a healthcare provider before taking calcium supplements.

Smoking: People who smoke absorb less calcium from the stomach and might require calcium supplements.

Stroke: Taking calcium supplements for 5 or more years might increase the chance of developing dementia in people who have had a stroke. More research is needed to know if calcium supplements should be avoided after a stroke.

Effectiveness

Dosing & administration

Calcium is an essential nutrient found in many foods, including dairy products, kale, broccoli, and calcium-enriched citrus juices. The amount that should be consumed on a daily basis is called the recommended dietary allowance (RDA). For all adults 19-50 years of age and for males 51-70 years of age, the RDA is 1000 mg. For females 51 years and older, the RDA is 1200 mg. While pregnant and breast-feeding, the RDA is 1300 mg for those under 19 years of age and 1000 mg for those 19 years and older. In children, the RDA depends on age.

In supplements, calcium has most often been used by adults in doses of 500-1500 mg by mouth daily. Don't take more than 2000-2500 mg daily unless under the supervision of a healthcare provider. Speak with a healthcare provider to find out what type of product and dose might be best for a specific condition.

Interactions with pharmaceuticals

Aluminum

Interaction Rating=Moderate Be cautious with this combination.

Calcium citrate can increase how much aluminum the body absorbs from aluminum hydroxide. This increase in aluminum levels can cause serious side effects, especially in people with kidney disease. But not all forms of calcium have this effect. Calcium acetate does not appear to increase aluminum levels.

Antibiotics (Quinolone antibiotics)

Interaction Rating=Moderate Be cautious with this combination.

Calcium might decrease how well some antibiotics work. In the gut, calcium binds to antibiotics known as "quinolones." This can decrease the amount of these drugs that the body absorbs. To avoid this interaction, take these drugs at least 2 hours before or 4 to 6 hours after calcium.

Antibiotics (Tetracycline antibiotics)

Interaction Rating=Moderate Be cautious with this combination.

Calcium might decrease how well some antibiotics work. In the gut, calcium binds to antibiotics known as "tetracyclines." This can decrease the amount of these drugs that the body absorbs. To avoid this interaction, take these drugs at least 2 hours before or 4 to 6 hours after calcium.

Bictegravir/Emtricitabine/Tenofovir alafenamide (Biktarvy)

Interaction Rating=Moderate Be cautious with this combination.

Calcium can decrease how much bictegravir/emtricitabine/tenofovir alafenamide the body absorbs from the stomach. To avoid this interaction, take calcium and bictegravir/emtricitabine/tenofovir alafenamide with food. Do not take bictegravir/emtricitabine/tenofovir alafenamide on an empty stomach with, or 2 hours after, calcium containing products.

Bisphosphonates

Interaction Rating=Moderate Be cautious with this combination.

Calcium can decrease how much bisphosphonate the body absorbs, which can decrease the effects of bisphosphonates. To avoid this interaction, take bisphosphonates at least 30 minutes before calcium or at a different time of day.

Calcipotriene (Dovonex)

Interaction Rating=Moderate Be cautious with this combination.

Calcipotriene is a drug that is similar to vitamin D. Vitamin D helps the body absorb calcium. Taking calcium supplements along with calcipotriene might increase levels of calcium too much.

Ceftriaxone (Rocephin)

Interaction Rating=Major Do not take this combination.

Administering intravenous ceftriaxone and calcium together can result in life-threatening damage to the lungs and kidneys. Calcium should not be administered intravenously within 48 hours of intravenous ceftriaxone. This interaction is not a concern when calcium is taken by mouth.

Digoxin (Lanoxin)

Interaction Rating=Moderate Be cautious with this combination.

Calcium can affect your heart. Digoxin is used to help your heart beat stronger. Taking calcium along with digoxin might increase the effects of digoxin and lead to an irregular heartbeat. If you are taking digoxin, talk to your doctor before taking calcium supplements.

Diltiazem (Cardizem, others)

Interaction Rating=Moderate Be cautious with this combination.

Taking large amounts of calcium along with diltiazem might decrease the effects of diltiazem.

Dolutegravir (Tivicay)

Interaction Rating=Major Do not take this combination.

Taking calcium along with dolutegravir can reduce blood levels of dolutegravir. This might decrease the effects of dolutegravir. To avoid this interaction, dolutegravir should be taken 2 hours before or 6 hours after taking calcium.

Elvitegravir (Vitekta)

Interaction Rating=Major Do not take this combination.

Taking calcium along with elvitegravir can reduce blood levels of elvitegravir. This might decrease the effects of elvitegravir. To avoid this interaction, elvitegravir should be taken 2 hours before or 2 hours after taking calcium.

Levothyroxine (Synthroid, others)

Interaction Rating=Moderate Be cautious with this combination.

Calcium can decrease how much levothyroxine the body absorbs. Taking calcium along with levothyroxine might decrease the effects of levothyroxine. Levothyroxine and calcium should be taken at least 4 hours apart.

Lithium

Interaction Rating=Moderate Be cautious with this combination.

Long-term lithium use can increase calcium levels in the blood. Taking lithium with calcium supplements might increase calcium levels too much.

Medications for high blood pressure (Calcium channel blockers)

Interaction Rating=Minor Be watchful with this combination.

Calcium channel blockers are a type of medicine used for high blood pressure. Calcium may decrease the effects of calcium channel blockers when given by IV. But taking calcium supplements by mouth or consuming foods containing calcium does not seem to have this effect.

Raltegravir (Isentress)

Interaction Rating=Moderate Be cautious with this combination.

Taking calcium along with raltegravir for several months might reduce blood levels of raltegravir and decrease its effects. Taking a single dose of calcium along with raltegravir does not appear to affect blood levels of raltegravir.

Sotalol (Betapace)

Interaction Rating=Moderate Be cautious with this combination.

Taking calcium with sotalol can decrease how much sotalol the body absorbs. Taking calcium along with sotalol might decrease the effects of sotalol. To avoid this interaction, take calcium at least 2 hours before or 4 hours after taking sotalol.

Verapamil (Calan, others)

Interaction Rating=Moderate Be cautious with this combination.

Taking large amounts of calcium along with verapamil might decrease the effects of verapamil.

Water pills (Thiazide diuretics)

Interaction Rating=Moderate Be cautious with this combination.

Some "water pills" increase the amount of calcium in the body. Taking large amounts of calcium with some "water pills" might cause there to be too much calcium in the body. This could cause serious side effects, including kidney problems.

Interactions with herbs & supplements

Iron: Calcium supplements can decrease the absorption of iron from foods. In people who have enough iron stored in their bodies, taking calcium does not cause a problem over the long term. But people at high risk for iron deficiency should take calcium supplements at bedtime instead of with meals.
Lycopene: Taking calcium together with lycopene may decrease the amount of lycopene that the body absorbs. To avoid this interaction, people should take calcium supplements at bedtime instead of with meals.
Magnesium: Calcium supplements can decrease the absorption of magnesium from the diet, but only at very high doses (2600 mg daily). People at high risk for magnesium deficiency should take calcium supplements at bedtime instead of with meals.
Vitamin D: Taking vitamin D along with calcium increases the absorption of calcium. This might increase the risk of calcium levels becoming too high in some people.
Zinc: Calcium supplements can decrease the absorption of zinc from the diet. In people who have enough zinc stored in their bodies, taking calcium does not cause a problem over the long term.

Interactions with foods

Eating foods and drinking beverages high in caffeine, sodium, or protein causes the body to remove calcium. You might need to consume more calcium in the diet or take a calcium supplement if you have a diet high in these ingredients. Also, eating foods high in fiber can reduce how much calcium the body absorbs. Don't eat high fiber foods within two hours of taking calcium supplements.

Taking calcium supplements can decrease how much iron, zinc, and magnesium the body absorbs from foods. But this doesn't seem to be a problem for people with normal levels of these nutrients.