Calcium: Benefits, Dosage, Foods, Interactions and More

While calcium is often touted for helping build strong bones, there's actually way more to this essential mineral.

In fact, calcium is considered a nutrient of public health concern, according to the Dietary Guidelines for Americans. Translation: Many U.S. adults don't get enough calcium and the health consequences of inadequate intake are no joke.

To fully understand just how critical calcium is for achieving optimal health, we're breaking down the various functions of calcium in the body, the best food sources of calcium, what happens when we get too much or too little of it and when supplementation may be recommended.

"Calcium is the most abundant mineral in our bodies," Sarah Rueven, RDN, a New York City-based registered dietitian and founder of the private practice Rooted Wellness, says.

"It is required for so many important functions, including maintenance of strong bones and teeth, blood clotting, nerve signal transmission, muscle movement and cardiovascular health."

Calcium naturally occurs in everyday foods you probably already eat (like dairy). Still, Americans don't seem to be meeting their daily calcium needs across the board.

Calcium performs critical functions in the body, from supporting bone health to maintaining muscle function and more.

About 99 percent of the body's calcium is located in our bones and teeth, according to the National Institutes of Health.

Throughout our lives, the makeup of our bones constantly shifts, with calcium being added and removed from them depending on blood calcium levels and how much of the mineral we get via the diet.

"Anytime that we aren't getting enough calcium in our diet, calcium is pulled from our bones to maintain calcium homeostasis in the blood," Rueven says. If this continues over time, bone mineral density will decline, raising one's risk of osteoporosis.

To prevent bone loss, aim to meet your daily calcium needs as well as your vitamin D needs — because vitamin D is needed for calcium absorption. Without enough vitamin D, your body can't make the hormone calcitriol, aka the active form of vitamin D, per the NIH.

Doing weight-bearing exercises like resistance training is also critical for maintaining strong bones.

Calcium is involved in both the constriction and dilation (or relaxation) of blood vessels, making it a key player in maintaining healthy blood pressure levels, per Harvard Health Publishing.

Some studies have also shown that higher calcium intakes may improve blood pressure levels even in people who do not have hypertension, according to Cochrane.

When the brain signals the muscle to contract, the body pulls calcium from the blood into the muscle. The calcium binds with a protein called troponin and draws it out of position, and the tropomyosin (another protein) follows the troponin because the two proteins are linked together.

When the troponin and tropomyosin move, this activates specific enzymes to produce energy to contract the muscle, per Oregon State University.

If you don't get enough calcium from your diet, your body will end up pulling calcium from your bones to fuel muscle contractions (and other important functions). That's why a calcium deficiency can negatively affect all the muscles in your body, and people with severe calcium deficiencies might experience muscle weakness.

"Calcium is found in dairy products, dark leafy green vegetables, legumes, fish with bones like canned salmon and sardines, soy products, nuts and seeds and calcium-fortified almond milks and orange juice," Rueven says.

Some of the top foods high in calcium include:

• Yogurt: 415 mg, 32% DV in 1 cup
• Mozzarella: 349 mg, 27% DV in 1.5 oz.
• Canned sardines (with bones): 325 mg, 25% DV in 2 oz.
• 2% milk: 293 mg, 23% DV in 1 cup
• Fortified firm tofu: 253 mg, 19% DV in 1/2 cup
• Canned salmon (with bones): 181 mg, 14% DV in 3 oz.
• Kale: 94 mg, 7% DV in 1 cup cooked
  
• Chia seeds: 76 mg, 6% DV in 1 tbsp

Want to put more calcium on your plate? Rueven recommends adding chia or sesame seeds to salads, yogurt bowls and protein smoothies.

"It's also a good idea to increase your intake of plant-based proteins like beans and lentils," she says. "Beans and lentils contain some calcium while also being high in protein, iron and fiber."

"A calcium deficiency (hypocalcemia) can increase your risk for osteoporosis, a condition in which bones become weak and brittle and are more prone to fracture," Rueven says. "This is why it's so important to get enough calcium in the diet."

Getting enough calcium early in life is important since bone mineral density peaks around age 25 to 30 and then declines as we age, according to the American Academy of Orthopaedic Surgeons.

"Children who do not get enough calcium in their diet are at risk for stunted growth and osteoporosis later in life," Rueven says.

"Since the majority of bone development happens during adolescence and early adulthood, an inadequate intake of calcium during those years can have detrimental effects on bone health later in life."

Also important: Older women require more calcium than men. "As women go through menopause, estrogen levels decline," Rueven says. "Estrogen protects bones by promoting the activity of osteoblasts, or bone-building cells, which is why women need more calcium than men once they reach menopause."

Individuals with GI disorders like celiac disease, lactose intolerance or inflammatory bowel disease are also at a greater risk of calcium deficiency since the conditions can result in alterations in nutrient absorption.

Additional factors like other components in foods (think: phytic acid, oxalic acid) and alcohol can also contribute to reduced calcium absorption in the body, per the NIH.

"It is next to impossible to get too much of a nutrient from diet alone," Rueven says. "In contrast, it is easy to get an excess of a nutrient from supplementation and more is not always better when it comes to calcium."

Though more research is needed, some studies have suggested that large doses of calcium supplements, especially when taken without food, can increase the risk of kidney stones in susceptible people, per a September 2014 review in ‌Translational Andrology and Urology‌‌.‌

Hypercalcemia, or high calcium levels in the blood, is associated with adverse GI symptoms, including stomach pain, nausea, vomiting and constipation, per the Mayo Clinic.

Calcium carbonate supplements in particular have been linked to a greater risk of constipation.

Some studies have suggested that men who take high-dose calcium supplements may be at a greater risk of heart complications like heart disease and heart attack, according to the Mayo Clinic.

But, experts report that more research is needed before causation can be concluded.

Calcium supplements have been shown to interact with a number of common drugs, per the NIH.

• Bisphosphonates
• fluoroquinolone and tetracycline antibiotics
• Levothyroxine
• Phenytoin
• Tiludronate disodium
• Thiazide-type diuretics: These can increase calcium absorption, potentially resulting in hypercalcemia, or high calcium levels in the blood.
• Corticosteroids: Long-term usage can lower calcium levels in the body, increasing the risk of bone density loss.

"Before starting a supplement, I recommend that all of my clients speak to their doctor first," Rueven says. Starting any dietary supplement without information about your levels is not recommended.

If a supplement is recommended by your doctor or registered dietitian, look for one made by a brand that's third-party tested, follows the FDA's CGMPs (Current Good Manufacturing Practices) and is committed to science and transparency.

USP (U.S. Pharmacopeia) stamps are also good indicators of reliable supplement brands.

Calcium carbonate and calcium citrate are two common forms of calcium supplements.

"Calcium carbonate is cheaper and contains the most elemental calcium — 40 percent — meaning you'll get more calcium per pill," Rueven tells LIVESTRONG.com.

Calcium phosphate (or tricalcium phosphate) is a close second, with 39 percent elemental calcium.

"Calcium citrate provides about 20 percent elemental calcium, so you may need to end up taking more pills to get enough calcium." It's not uncommon for calcium supplements to also contain vitamin D to optimize absorption.

Calcium carbonate is best taken with meals, while calcium citrate can be taken solo or with food.

In the end, "which form you take is dependent on your own calcium needs and your individual response to the different forms," Rueven says.