Dosing, Side effects, Interaction and Supplements of Calcium

We need to consume a certain amount of calcium to build and maintain strong bones and healthy communication between the brain and other parts of the body.

May 15, 2019

We need to consume a certain amount of calcium to build and maintain strong bones and healthy communication between the brain and other parts of the body. Calcium is found naturally in several foods such as milk and dairy products, kale and broccoli, as well as the calcium-enriched citrus juices, mineral water, canned fish with bones, and soy products processed with calcium. It is also added to certain products, and supplements are available.


The following doses have been studied in scientific research and is recommended:

By Mouth:

For preventing low calcium levels:

1 gram elemental calcium daily is typically used.

For heartburn:

Calcium carbonate as an antacid is usually 0.5-1.5 grams as needed.

To reduce phosphates in adults with chronic renal failure:

The initial dose of calcium acetate is 1.334 grams (338 mg elemental calcium) with each meal, increasing to 2-2.67 grams (500-680 mg elemental calcium) with each meal if necessary.

For prevention of weak bones (osteoporosis):

Doses of 1-1.6 grams elemental calcium daily from foods and supplements. Osteoporosis treatment guidelines in North America currently recommend 1200 mg daily of calcium.

For prevention of bone loss in premenopausal women over 40:

A dose of 1 gram.

For pregnant women with low dietary calcium intake:

The dose for increasing fetal bone density ranges from 300-1300 mg/day beginning at gestation week 20-22.

For premenstrual syndrome (PMS):

1-1.2 grams calcium per day as calcium carbonate.

For reducing thyroid hormone levels in people with chronic renal failure:

2-21 grams calcium carbonate.

To prevent bone loss in people taking corticosteroid drugs:

Divided daily doses of 1 gram of elemental calcium daily.

For high blood pressure:

1-1.5 grams calcium daily.

For preventing high blood pressure during pregnancy (pre-eclampsia):

1-2 grams elemental calcium daily as calcium carbonate.

For preventing colorectal cancer and recurrent colorectal benign tumors (adenomas):

Calcium 1200-1600 mg/day.

For high cholesterol:

1200 mg daily with or without vitamin D 400 IU daily has been used in conjunction with a low-fat or calorie-restricted diet.

For preventing fluoride poisoning in children:

Calcium 125 mg twice daily, in combination with ascorbic acid and vitamin D.

For weight loss:

Increasing calcium consumption from dairy products to total intake of 500-2400 mg/day in combination with a calorie-restricted diet has been used.
Calcium carbonate and calcium citrate are the two most commonly used forms of calcium.
Calcium supplements are usually divided into two doses daily in order to increase absorption. It is best to take calcium with food in doses of 500 mg or less.
The Institute of Medicine publishes a recommended daily allowance (RDA) for calcium which is an estimate of the intake level necessary to meet the requirements of nearly all healthy individuals in the population. The current RDA was set in 2010. The RDA varies based on age as follows:

  • Age 1-3 years, 700 mg
  • 4-8 years, 1000 mg
  • 9-18 years, 1300 mg
  • 19-50 years, 1000 mg
  • Men 51-70 years, 1000 mg
  • Women 51-70 years, 1200 mg
  • 70+ years, 1200 mg
  • Pregnant or Lactating (under 19 years), 1300 mg
  • Pregnant or Lactating (19-50 years), 1000 mg.

The Institute of Medicine also sets the daily tolerable upper intake level (UL) for calcium based on age as follows:

  • Age 0-6 months, 1000 mg
  • 6-12 months, 1500 mg
  • 1-3 years, 2500 mg
  • 9-18 years, 3000 mg
  • 19-50 years, 2500 mg
  • 51+ years, 2000 mg.

Doses above these levels should be avoided. Doses over the recommended daily intake level of 1000-1300 mg/day for most adults have been associated with an increased risk of heart attack. However, you can continue consuming adequate amounts of calcium to meet daily requirements, but not excessive amounts of calcium. Be sure to consider total calcium intake from both dietary and supplemental sources and try not to exceed 1000-1300 mg of calcium per day. To figure out dietary calcium, count 300 mg/day from non-dairy foods plus 300 mg/cup of milk or fortified orange juice.

Side Effects & Safety:

  • Calcium is likely safe for most people when taken by mouth or when given intravenously (by IV) and appropriately. Calcium can cause some minor side effects such as belching or gas.
  • Calcium is possibly unsafe for both adults and children when taken by mouth in high doses. Avoid taking too much calcium.
  • Higher doses increase the chance of having serious side effects. Doses over the recommended daily requirement of 1000-1300 mg daily for most adults might increase the chance of heart attack.

Special Precautions & Warnings:

Special precaution should be taken while using calcium for the below conditions:

Pregnancy and breast-feeding:

Calcium is likely safe when taken by mouth in recommended amounts during pregnancy and breast-feeding. There is not enough information available on the safety of using calcium intravenously (by IV) during pregnancy and breastfeeding.

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. However, low acid levels in the stomach do not appear to reduce calcium absorption if calcium is taken with food. People with achlorhydria are advised to take calcium supplements with meals.

High levels of phosphate in the blood (hyperphosphatemia) or low levels of phosphate in the blood (hypophosphatemia):

Calcium and phosphate have to be in balance in the body. Taking too much calcium can cause imbalance and cause harm. Don't take extra calcium without the supervision of your health provider.

Under-active thyroid (hypothyroidism):

Calcium can interfere with thyroid hormone replacement treatment. Separate calcium and thyroid medications by at least 4 hours.
Too much calcium in the blood (as in parathyroid gland disorders and sarcoidosis):
Calcium should be avoided if you have one of these conditions.

Poor kidney function:

Calcium supplementation can increase the risk of having too much calcium in the blood in people with poor kidney function.


People who smoke absorb less calcium from the stomach.


Do not take the below combination as this can have major interaction.

Ceftriaxone (Rocephin) interacts with Calcium:

Administering intravenous ceftriaxone and calcium can result in life-threatening damage to the lungs and kidneys. Calcium should not be administered intravenously within 48 hours of intravenous ceftriaxone.
Be cautious with the below combination as these can have moderate interaction:

Antibiotics (Quinolone antibiotics) interacts with Calcium:

Calcium might decrease how much antibiotic your body absorbs. Taking calcium along with some antibiotics might decrease the effectiveness of some antibiotics. To avoid this interaction, take calcium supplements at least 1 hour after antibiotics. Some of these antibiotics that might interact with calcium include ciprofloxacin (Cipro), enoxacin (Penetrex), norfloxacin (Chibroxin, Noroxin), sparfloxacin (Zagam), and trovafloxacin (Trovan).

Antibiotics (Tetracycline antibiotics) interacts with Calcium:

Calcium can attach to some antibiotics called tetracyclines in the stomach. This decreases the amount of tetracyclines that can be absorbed. Taking calcium with tetracyclines might decrease the effectiveness of tetracyclines. To avoid this interaction take calcium 2 hours before or 4 hours after taking tetracyclines. Some tetracyclines include demeclocycline (Declomycin), minocycline (Minocin), and tetracycline (Achromycin, and others).

Bisphosphonates interacts with Calcium:

Calcium can decrease how much bisphosphate your body absorbs. Taking calcium along with bisphosphates can decrease the effectiveness of bisphosphate. To avoid this interaction, take bisphosphonate at least 30 minutes before calcium or later in the day.Some bisphosphonates include alendronate (Fosamax), etidronate (Didronel), risedronate (Actonel), tiludronate (Skelid), and others.

Calcipotriene (Dovonex) interacts with Calcium:

Calcipotriene (Dovonex) is a drug that is similar to vitamin D. Vitamin D helps your body absorb calcium. Taking calcium supplements along with calcipotriene (Dovonex) might cause the body to have too much calcium.

Digoxin (Lanoxin) interacts with Calcium:

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

Diltiazem (Cardizem, Dilacor, Tiazac) interacts with Calcium:

Calcium can affect your heart. Diltiazem (Cardizem, Dilacor, Tiazac) can also affect your heart. Taking large amounts of calcium along with diltiazem (Cardizem, Dilacor, Tiazac) might decrease the effectiveness of diltiazem (Cardizem, Dilacor, Tiazac).

Levothyroxine interacts with Calcium:

Levothyroxine is used for low thyroid function. Calcium can decrease how much levothyroxine your body absorbs. Taking calcium along with levothyroxine might decrease the effectiveness of levothyroxine. Levothyroxine and calcium should be taken at least 4 hours apart. Some brands that contain levothyroxine include Armour Thyroid, Eltroxin, Estre, Euthyrox, Levo-T, Levothroid, Levoxyl, Synthroid, Unithroid, and others.

Lithium interacts with Calcium:

Sotalol (Betapace) interacts with Calcium:

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

Verapamil (Calan, Covera, Isoptin, Verelan) interacts with Calcium:

Calcium can affect your heart. Verapamil (Calan, Covera, Isoptin, Verelan) can also affect your heart. Do not take large amounts of calcium if you are taking verapamil (Calan, Covera, Isoptin, Verelan).

Water pills (Thiazide diuretics) interacts with Calcium:

Some 'water pills' increase the amount of calcium in your 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. Some of these 'water pills' include chlorothiazide (Diuril), hydrochlorothiazide (HydroDIURIL, Esidrix), indapamide (Lozol), metolazone (Zaroxolyn), and chlorthalidone (Hygroton).
Be watchful with the below combination as these can have minor interaction:

Estrogens interacts with Calcium:

Estrogen helps your body absorb calcium. Taking estrogen pills along with large amounts of calcium might increase calcium in the body too much. Estrogen pills include conjugated equine estrogens (Premarin), ethinyl estradiol, estradiol, and others.
Medications for high blood pressure (Calcium channel blockers) interacts with Calcium:
Some medications for high blood pressure affect calcium in your body. These medications are called calcium channel blockers. Getting calcium injections might decrease the effectiveness of these medications for high blood pressure. Some medications for high blood pressure include nifedipine (Adalat, Procardia), verapamil (Calan, Isoptin, Verelan), diltiazem (Cardizem), isradipine (DynaCirc), felodipine (Plendil), amlodipine (Norvasc), and others.

Calcium Supplements:

The amount of calcium you need from a supplement depends on how much you get from food. Try to get the daily amount recommended from food. Take supplement only if it is needed to make up any shortfall. In general, you shouldn't take supplements that you don't need as over dose may have side effects. If you get enough calcium from foods, don't take a supplement. There is no added benefit to taking more calcium than you need.
Calcium supplements are available without a prescription in a wide range of preparations (including chewable and liquid) and in different amounts. Selection depends on the patient's needs and preferences, their medical condition, and whether they are on any medications. Choose the one that meets your needs for convenience, cost, and availability. When choosing a supplement, keep the following in mind:

Choose brand-name supplements with proven reliability:

Look for labels that state “purified” or have the USP (United States Pharmacopeia) symbol. The “USP Verified Mark” on the supplement label means that the USP has tested and found the calcium supplement to meet its standards for purity and quality.

Read the product label carefully:

This is to determine the amount of elemental calcium, which is the actual amount of calcium in the supplement, as well as how many doses or pills you have to take. When reading the label, pay close attention to the 'amount per serving' and 'serving size.
Elemental calcium is the pure mineral that exists in its natural form with other compounds. Calcium supplements may contain different kinds of calcium compounds and varying amounts of elemental calcium, for example:

  • Calcium carbonate contains 40 percent elemental calcium. This type is more commonly available. It is relatively cheap and convenient. It is absorbed best when taken with food because it needs stomach acid to be absorbed.
  • Calcium lactate contains 13 percent elemental calcium.
  • Calcium gluconate contains 9 percent elemental calcium
  • Calcium citrate contains 21 percent elemental calcium. Calcium citrate can be taken with or without food. It is useful for patients with inflammatory bowel disease, achlorhydria, and some absorption disorders.

Vitamin D is added to many calcium supplements because it encourages the synthesis of proteins in the body, which make the absorption of calcium possible.

Calcium is absorbed best when taken in amounts of 500-600 mg or less:

This is the case for both foods and supplements. Try to get your calcium-rich foods and/or supplements in small amounts throughout the day, preferably with a meal.
Each intake of supplements should not exceed 600 milligrams. If more than that is consumed in one go, the excess will not be absorbed as well. However, taking your calcium all at once is better than not taking it at all.

Take (most) calcium supplements with food:

Eating food produces stomach acid that helps your body absorb most calcium supplements. The one exception to the rule is calcium citrate, which can absorb well when taken with or without food.

When starting a new calcium supplement, start with a smaller amount to better tolerate it:

When switching supplements, try starting with 200-300 mg every day for a week, and drink an extra 6-8 ounces of water with it. Then gradually add more calcium each week.

Side effects from calcium supplements, such as gas or constipation may occur:

If increasing fluids in your diet does not solve the problem, try another type or brand of calcium. It may require trial and error to find the right supplement for you, but fortunately there are many choices. Talk with your healthcare provider or pharmacist about possible interactions between prescription or over-the-counter medications and calcium supplements.