Can You Take Calcium and Iron Together?

Medically reviewed by Suzanne Fisher, RD

Calcium and iron are two important minerals found in a variety of foods. However, many people don't get enough of either in their diet.

Not taking in enough calcium can lead to osteoporosis, characterized by weak and fragile bones that are more likely to break. Not taking in enough iron can lead to fatigue and other symptoms from anemia, a condition in which you don’t have enough healthy red blood cells.

Some people might have low levels in both minerals. To increase their levels, a healthcare provider may recommend they take both a calcium and iron supplement. While it may be safe and beneficial to take both supplements, you should avoid taking them together since calcium can interfere with iron's absorption.

Here's what you should know if you need to take calcium and iron.

Benefits of Calcium

Calcium plays a role in different bodily processes, like maintaining the heart’s electrical rhythm. Some people can get enough calcium through their diet alone, as the mineral is found in many foods, such as dairy products, vegetables like broccoli, and fortified products like cereals that contain added vitamins and minerals.

Some people don't take in enough calcium through their diet. Even if you don't get enough, your body usually does a good job of regulating the concentration of calcium in the blood. But the reason your body is able to maintain blood levels of calcium without proper dietary intake is because your body will start to take the calcium from your bones and move the calcium into the bloodstream.

That’s why getting enough calcium can be so helpful in preventing brittle bones from osteoporosis— with enough calcium in your blood to begin with, your body doesn't need to take calcium from your bones. If a healthcare provider determined you don't get enough dietary calcium, a calcium supplement can help ensure you are taking in enough calcium and maintain bone health.

Calcium’s potential benefits for other health conditions aren’t as well-established.

Some research has shown that getting enough calcium may reduce the risk of some cancers such as colon cancer, but the relationship is not yet clear.

People who take in less calcium in their diet may be at greater risk of high blood pressure (hypertension), stroke, and heart attack. Meaning, taking in enough calcium can prevent the increased risk of these conditions. However, the findings of the relationships are mixed, with some studies showing an increased risk of heart problems among people who take in more calcium than needed.  

Benefits of Iron

Iron is an essential mineral found in many foods, including meat, seafood, nuts, beans, vegetables, and fortified products like cereals.

Iron is an important part of hemoglobin, the protein that carries oxygen around your body inside your red blood cells. Iron is especially important for its role in preventing anemia. In iron-deficiency anemia, a person doesn’t have enough iron in their body to make new healthy red blood cells. Iron-deficiency anemia can develop from not getting enough iron through your diet. Supplementing with iron may help increase and maintain your levels if a blood test shows your levels are low.

Although iron is most known for its role in the prevention of anemia, the mineral performs other functions in the body. Iron promotes growth in children, enhances neurological development, and supports the immune system.

Benefits of Taking Calcium and Iron Together

People who are deficient in both minerals may need to take a supplement for each.

There are some people who may be likelier to be deficient in both. This includes people following certain diets that may be low in both iron and calcium, like a vegan diet, especially if you aren’t eating many fortified foods. People with a medical condition like Crohn's disease that prevents the proper absorption of minerals from the diet might benefit from taking both calcium and iron.

However, it might not be best to take calcium and iron together. Calcium can decrease iron's absorption, so if you need to take both supplements, it's best to take them at separate times.

How To Take a Combination of Calcium and Iron

If you are deficient in calcium and iron, it is best to take the supplements at separate times. Taking the supplements at different times may avoid any absorption interference.

Calcium tends to be better absorbed if you take it with a meal, especially if you are using the calcium carbonate type. Calcium supplements that come in liquid or powder form might also be better absorbed, though that’s unclear. If you are at particularly high risk for iron deficiency, you might want to consider taking the calcium supplement at bedtime, instead of with meals, to avoid interfering with any dietary iron absorption.

Iron, which comes in different forms including pills and liquids, might best be absorbed if you take it on an empty stomach at least an hour before meals. Taking iron supplements with food can decrease iron absorption by 40-75%, partially due to how calcium and iron bind in the intestines. Some people might find they get an upset stomach if they take iron on an empty stomach. If that's the case for you and you want to take iron with food, avoid taking it with dairy, coffee, tea, or cereals.

Dosage

People usually take 500-1,500 milligrams (mg) of calcium supplements a day. If you are taking the supplement with food, you likely don't need to take more than 500 mg of the supplement since calcium is easiest absorbed when taken with food.

How much iron your supplement provides depends on whether you're taking iron alone or as part of a multivitamin. Multivitamins designed for women that contain iron typically provide 18 mg of iron. Multivitamins for men or solder adults usually contain less or no iron. Supplements that contain only iron can provide as much as 65 mg of iron.

A healthcare provider can help you figure out which dosage of each is right for you based on factors like your age, sex, current levels of the minerals, and diet.

The recommended dietary allowance (RDA)—which is the average daily level of intake that sufficiently meets most people's nutrient requirements—of calcium is 1,300 mg for 18 year olds and 1,000 mg for people 19-50. The RDA for men who are 51–70 is 1,000 mg. The RDA for women 51–70 as well as anyone over 70 is 1,200 mg.

The RDA for iron among adults ranges from 8-27 mg. The amount depends on sex, age, pregnancy status, and lactation status. For instance, while it's recommended that men 19 or older have 8 mg of iron a day, women who are pregnant may need as much as 27 mg a day. Recommended iron intake is also higher (18-15 mg) for people who menstruate to make up for the lost iron and blood during their period.

Is It Safe To Take Calcium and Iron Together?

If you aren’t getting enough calcium and iron, it’s generally safe to take both as part of your supplement regimen. But because there are potential side effects from taking in too much calcium and iron, only people who have been directed by a healthcare provider to take the supplements should be using them.

Potential Drug Interactions

Both calcium and iron can interact with various drugs. The supplements might increase or decrease the medications' absorption, which might impact their effectiveness or side effects. Sometimes, taking a specific drug will increase or decrease the amount of calcium or iron in the body.

Calcium and iron can decrease the absorbency of the following drugs:

• Antibiotics, namely quinolone antibiotics such as Cipro (ciprofloxacin) and tetracycline antibiotics such as Monodox (doxycycline) or Rocephin (ceftriaxone)

• Bisphosphonates, a class of medications that can prevent or slow osteoporosis

• Tivicay (dolutegravir), an HIV drug

• Levothyroxine, a synthetic hormone used to treat underactive thyroid (hypothyroidism) that is sold under brand names like Synthroid and Levoxyl

Calcium and iron can each interact with other medications as well. For instance, calcium can interact with the arrhythmia medication sotalol (sold under brand names like Betapace and Sorine) while iron may interact with the high blood pressure drug methyldopa.

You still might be able to take calcium and iron if you use these medications, but you may have to take them at different times.

What To Look For

The two most commonly available forms of calcium are calcium carbonate and calcium citrate. Calcium citrate tends to be a little better absorbed.

Iron is available in different forms, too, including iron salts like ferrous sulfate, ferrous gluconate, and ferrous fumarate. Enteric formulations and slow-release formulations may be a little easier on the stomach than other kinds, but dosage is the most important factor in reducing side effects.

Ideally, find supplements that say a third party has tested the product. Labels on the packaging from organizations like the NSF or the United States Pharmacopeia (USP) mean the product has been tested for purity.

Can You Take Too Much Calcium or Iron?

It is possible to take too much calcium or iron. That's why it's important people use both supplements only after a healthcare provider has told them to do so.

Both nutrients have a tolerable upper intake level (UL), which is the maximum daily intake of each nutrient from both food and supplements that is unlikely to cause adverse side effects. The UL for calcium is 1,000 mg for adults 19-50 as well as men 51-70. For women aged 51-70 as well as all adults 71 or older, the UL is 1,200 mg. The UL for iron is 45 mg for adults of any age or sex. Depending on your particular needs, a healthcare provider may recommend doses higher than the ULs.

Excessive calcium intake can lead to elevated levels of calcium in the blood (hypercalcemia). This condition can cause problems like kidney damage and life-threatening abnormal heart rhythms. Higher doses of calcium supplements—as much as 1,000 mg a day for seven years—may eventually lead to kidney stones.

Some evidence shows that having too much calcium may increase the risk of heart attack and stroke, especially if you are getting some of your calcium through supplements. These risks might be reduced if you take vitamin D along with your calcium.

Taking an excessive amount of iron in one sitting can damage your intestines and cause worse gastrointestinal effects than normal levels of iron might, such as inflammation of your stomach lining (gastritis). Even if the dosages are smaller but you take iron for longer than you need to, over time, iron overload can cause issues like liver damage, fatigue, joint pain, increased blood glucose, and decreased libido.

At the extreme, taking too much iron can be deadly. More commonly, it is children who experience adverse events from iron, such as by accidentally taking too many iron-containing multivitamins.

Related: Can You Take Vitamin D and Calcium Together?

Side Effects of Taking a Combination of Calcium and Iron

Some of the most common potential side effects of calcium are constipation, diarrhea, gas, and stomach upset.

Iron's most common side effects are similar to those of calcium. Iron supplements may cause abdominal pain, diarrhea, constipation, nausea, and vomiting. Side effects are more likely at higher doses.

In some cases, side effects might be worsened by taking the two supplements together.

A Quick Review

Calcium and iron are two essential minerals. It’s important to get enough of both to prevent conditions like osteoporosis and anemia. If a healthcare provider determines your levels of both are low, you might be instructed to take calcium and iron supplements. While it is likely safe to take both, you should take calcium and iron at different times throughout the day to optimize their absorption. Before starting both supplements, check to with your healthcare provider about the dosages that are right for you as well as whether there are interactions with any medications you are taking.

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