What is calcium and why do you need it?

Strong bones and teeth thrive on calcium. But more than just that, calcium is necessary for other daily, vital functions that go on behind the scenes: muscle contraction; nerve conduction; and the activity of your heart, blood and cells.

About 99% of calcium is stored in our bones, with the remaining 1% in blood, muscle and other tissues. Our body is pretty savvy when it comes to monitoring the precise amount of calcium it needs, transporting it away from the bones, which act somewhat like a reservoir, then doling it out into the body to maintain a steady stream of calcium in the blood.

But there’s a catch: If there’s not enough calcium in the blood to draw from, the body takes it from your bones, Smith said. Ideally, the calcium that’s “borrowed” from the bones will be replaced at a later point. But this doesn’t always happen, and it may contribute to osteoporosis over time.

Postmenopausal women are particularly prone to calcium deficiency because the loss of estrogen that occurs with menopause reduces both the amount of calcium your body absorbs and the amount of calcium your bones retain.

Levels of calcium in your blood can be measured with a calcium blood test. Rather than show the amount of calcium in your bones — that’s the job of a bone density test or DEXA scan — a calcium blood test can check for too much or too little calcium in your blood and can be a helpful indicator of your general health as well as many medical conditions, including bone or thyroid disease, parathyroid disorders, and kidney disease.

How much calcium do you need each day?

Most experts agree that women over 50, whose bodies generally absorb less calcium from food, need 1,200 mg of calcium per day.

Calcium needs vary, and not every woman requires the same amount of calcium. For instance, younger women between ages 19 and 50 need 1,000 mg of calcium daily. For pregnant and lactating women, 1,000 mg per day is recommended.

Can you get too much calcium?

If calcium is so good for you, does that mean more is better?

You might think so, but the answer is no.

Having too much calcium in your blood can cause a condition called hypercalcemia, which puts you at risk for kidney stones, cancer and constipation. There’s also research to suggest that for some people, too much calcium (especially from supplements) can accumulate in the blood vessels and may lead to heart problems. That’s why experts advise women over 50 not to get more than 2,000 mg daily from a combination of food and supplements. The upper limit for others is 2,500 mg a day.

It's important to be aware of certain medications that can keep your body from absorbing calcium well. These medications should not be taken at the same time as calcium supplements:

• Iron supplements
• Some antibiotics
• Thyroid medication
• Bisphosphonates (treatment for osteoporosis)
• Certain seizure medications

How to get calcium from food

Since our body can’t make calcium on its own, it gets what it needs through foods or supplements containing calcium.

Milk is not the only food that has a lot of calcium. Others include:

• Dairy products, such as yogurt and cheese
• Leafy greens (like kale)
• Broccoli
• Winter squash
• Edamame
• Canned sardines and salmon (especially with soft edible bones)
• Almonds and almond butter
• Fortified foods such as fruit juices and drinks, tofu, and cereals

Possible benefits of a calcium supplement

Calcium is best absorbed when you get it through food. “If you plan your diet to get plenty of calcium through food, that might be enough for your needs,” Smith said.

But food doesn’t always give you enough calcium, and according to many national nutrition surveys, most people are not getting enough. Why? Some people, like vegans or those who are lactose intolerant, find it tough to get enough calcium from food. Same goes for those who take corticosteroids on a long-term basis; have certain bowel or digestive diseases like celiac or inflammatory bowel disease, which can decrease your body’s ability to absorb calcium; or consume large amounts of sodium or protein, which can take calcium out of your body.

Two common forms of calcium supplements are calcium carbonate and calcium citrate. Calcium carbonate should be taken with a meal, since it needs stomach acid to dissolve, while calcium citrate can be taken anytime.

If you have trouble absorbing medication or if you take an iron supplement or medication for heartburn, then calcium citrate might be a better choice for you.

Everyone taking calcium supplements needs to pair it with vitamin D, which aids in calcium’s absorption. For people up to age 70, experts recommend 600 IU (international units) per day. After 70, you should increase your intake to 800 IU daily. The daily limit, according to the Institute of Medicine, should not go above 4,000 IU.

Since higher doses of calcium take longer to absorb, medical experts recommend not taking more than 500 mg in a single dose. If you require more, wait at least four hours before taking the second dose.

Before you turn to supplements, make sure you know the amount of calcium you’re getting from your food. “If you consume 500 mg of calcium in your diet, you may only need another 500 mg from a supplement,” Smith said. Calcium is listed on food labels, which base the daily recommended value on 1,200 mg of calcium. Because it can be confusing to calculate, you can turn to a quick guide, like this calcium calculator from the University of Alabama.

What else you need to know about taking calcium

It’s important to keep in mind that there are certain foods and medications that can increase your need for calcium. That’s because they cause your body to release more calcium into your urine, or they lower the ability of your gut to absorb it. Some examples include corticosteroids (like prednisone) and sodas containing phosphoric acid (like dark colas). Excessive alcohol consumption can also interfere with calcium balance by interfering with the production of vitamin D, which is needed for absorption.

There are benefits and risks to taking calcium supplements, said Smith, who recommended discussing any decisions to take supplements with your healthcare provider. “When taking a supplement, be sure to include other nutrients, like D3, K2 and magnesium, which can all aid absorption and how your body utilizes the calcium.”