Everything You Wanted To Know About Calcium

When it comes to calcium, it's important to think about both how much you're consuming and what calcium levels are like in the blood. Calcium is a macromineral — a mineral that humans need in relatively large amounts for good health. Calcium is also the most abundant mineral in the body. It pulls double duty, providing structure as the main component of our bones and acting as an electrolyte, allowing cells to communicate with one another (via News Medical). According to the National Institutes of Health (NIH), adult men have about 1,400 grams (3 pounds) of calcium in their bodies, while adult women have 1,200 grams (2.6 pounds). Calcium can be obtained from a variety of foods (particularly dairy products) and supplements. Having too little or too much calcium in the body can be dangerous, and how much calcium you consume (and what sources it comes from) may impact a number of health conditions, including osteoporosis, heart disease, and cancer.

Despite the importance of calcium, many people don't get enough. According to data analyzed by Oregon State University, more than 49% of American adults aren't consuming enough calcium to meet their body's needs.

Calcium and your bones

We've had it drilled into our heads since we were kids that calcium builds strong bones, and that's quite literally the case. According to American Bone Health, "when your body makes new bone tissue, it first lays down a framework of collagen. Then, tiny crystals of calcium from your blood spread throughout the collagen framework." These calcium crystals fill in all the gaps in the "web" of collagen. Collagen makes bones flexible, while calcium makes them strong.

The vast majority of calcium in the body — a staggering 98% of it — is found in our bones and teeth. But that doesn't necessarily mean it stays there forever. The body uses our bones as a sort of calcium bank, making deposits and withdrawals of this important nutrient as needed. (Although they contain calcium, our teeth don't experience this same type of fluctuation.) More than 99% of calcium in our bones is in the form of calcium hydroxyapatite, a compound made of calcium and phosphate (via the National Institutes of Health). When circulating levels of calcium are too low, hormonal triggers cause special bone cells called osteoclasts to break down bone, releasing calcium into the bloodstream (via American Bone Health). On the other hand, bone cells called osteoblasts create new bone, which requires calcium (via Healthline).

Calcium is an electrolyte

Calcium is famous as a bone-builder, but it actually plays numerous important roles in the body. As the National Institutes of Health (NIH) explained, the calcium in bones is used as a reservoir to ensure that there's enough circulating calcium to perform these other tasks. Although only 1% of the calcium in our bodies is involved in these roles, we couldn't function without it.

The other duties calcium performs stem from the fact that it's an electrolyte. As the Cleveland Clinic explained, "electrolytes are substances that have a natural positive or negative electrical charge when dissolved in water." Cells use electrolytes to transmit electrical charges, which are necessary for muscle and nerve function as well as many chemical reactions. Because they're so powerful, electrolyte levels are closely controlled by our bodies to ensure everything stays balanced. There are seven electrolytes; four with a positive charge (calcium, sodium, potassium, and magnesium) and three with a negative charge (chloride, phosphate, and bicarbonate). As an electrolyte, calcium assists with muscle contractions (including maintaining a normal heart rhythm), blood clotting, and the normal functioning of many enzymes (via the Merck Manual).

How much calcium we need and how much Americans are getting

Because calcium is so important for our health, guidelines on how much individuals should be consuming each day have been established by the Food and Nutrition Board (FNB) at the National Academies of Sciences, Engineering, and Medicine. For infants, this guideline has been set at an adequate intake (AI) of 200 mg for babies 6 months or younger and 260 mg for babies age 7–12 months. For children age 1–3 years, the recommended dietary allowance (RDA) is 700 mg, while children age 4–8 need 1,000 mg. Because puberty is a time of rapid growth, calcium needs are highest during this time. Tweens and teens age 9–18 require 1,300 mg daily, regardless of gender. During our prime adult years (age 19–50) both men and women have an RDA of 1,000 mg. Once women hit menopause (around age 51), the RDA increases to 1,200 mg. For men, the RDA shifts from 1,000 to 1,200 after they pass 70. Unlike some other micronutrients, calcium needs don't increase during pregnancy or breastfeeding.

But how much calcium are Americans actually getting? Average calcium intake from both food and supplements is 1,156 mg for adult men and 1,009 mg for adult women. But a whopping 39% of all individuals age four and older don't meet the minimum requirement for calcium intake, known as the estimated average requirement or EAR (via the National Institutes of Health).

Who's at risk for not getting enough calcium?

Anyone can fall short of the recommended dietary allowance (RDA) for calcium, but two groups are at particularly high risk. First, anyone who avoids dairy products is at increased risk for inadequate calcium intake, since dairy foods are the richest food sources of calcium. Individuals may avoid dairy products because they're following a vegan diet, have a milk allergy or lactose intolerance, or simply don't like them. While it may be harder for these individuals to get the calcium they need, it's definitely doable. Those with lactose intolerance can consume lactose-free dairy products or use Lactaid pills. There are other foods that naturally contain respectable amounts of calcium, and others have been fortified with calcium. Supplements are also an option.

The second at-risk group are postmenopausal women. The RDA for women increases from 1,000 mg to 1,200 mg once menopause hits, and some postmenopausal women don't increase their calcium intake accordingly. This is dangerous because the drop in estrogen levels that comes with menopause also hinders calcium absorption and increases loss of calcium in the urine. If calcium consumption isn't upped to compensate, bones can gradually become less dense, significantly increasing the risk of a fracture (via the National Institutes of Health).

Food sources of calcium

Some foods contain calcium naturally, while others are fortified with calcium to make it easier for Americans to meet their calcium needs. Foods typically fortified with calcium include fruit juices, tofu, and cereal. But a significant majority (72%) of the calcium Americans eat comes from dairy products and foods with dairy-based ingredients, and dairy is a particularly rich source of calcium (via the National Institutes of Health).

Yogurt is arguably the best natural source of calcium; a single one-cup serving contains 450 mg. One cup of milk contains 300 mg of calcium, while the same size serving of fortified soy milk contains 200–400 mg. A cup of sour cream contains 250 mg, and even your guilty pleasure ice cream contains a respectable 100 mg per half-cup serving. When it comes to fortified (calcium-set) tofu, calcium levels can vary wildly from 250 mg to 750 mg per 4-ounce serving. Fish that are eaten bones and all are also good natural sources of calcium; a 3-ounce serving of sardines has 370 mg. In general, grains are low in calcium, but fortified cereals can have as much as 1,000 mg per serving. Spinach, broccoli, and arugula are the best vegetable sources of calcium, while dried figs are the best fruit source of calcium. Fortified orange juice contains 300 mg per 8-ounce glass (via UCSF Health).

Calcium supplements

If you're worried you're not getting enough calcium from the food you eat, dietary supplements are always an option. According to the National Institutes of Health (NIH), approximately 22% of adult men, 32% of adult women, and 4%–8% of children take a supplement containing calcium. Calcium is sold as a standalone supplement, as part of targeted formulas for bone health (often with vitamin D), and is often included in daily multivitamins. Dosages in multivitamins generally range from 200 to 300 mg, while calcium-specific supplements tend to contain 500–600 mg. The two most commonly used forms of calcium in supplements are calcium carbonate (which is 40% elemental calcium) and calcium citrate (which is only 21% elemental calcium). Absorption is improved when calcium is taken with a meal, and those with low stomach acid will have better results with calcium citrate.

According to WebMD, calcium supplements are generally considered safe when taken at the recommended dosage. Side effects are minor and can include belching and gas. It's not a good idea, however, to take high doses of calcium that exceed the tolerable upper limit (UL) set for this mineral. The UL is 2,500 mg for adults age 19–50 and 2,000 mg for those over 50. Calcium supplements aren't usually recommended for those with kidney or parathyroid disorders.

Calcium supplements and medications

Although calcium supplements are generally considered safe, they can interact negatively with certain medications. For those with HIV taking either elvitegravir or dolutegravir, calcium can significantly impact the effectiveness of these antiviral drugs, so it's important to take them at separate times. Calcium can also bind to certain antibiotics in the digestive tract, making them less effective. This is especially true for quinolone and tetracycline antibiotics. For individuals with heart problems taking the medication digoxin, calcium supplements may increase this drug's activity and lead to an irregular heartbeat. Individuals with an underactive thyroid who are taking levothyroxine should be aware that calcium can reduce the potency of this medication. Taking calcium while also using thiazide diuretics ("water pills") or lithium (to treat bipolar disorder) may cause high levels of calcium. Ironically, calcium supplements may hinder the activity of bisphosphonates, a drugs used to prevent or slow bone loss. Supplements may also increase the effectiveness of calcipotriene, a drug that mimics vitamin D, which can lead to dangerously high levels of calcium in the blood (via WebMD).

When it comes to calcium and medications, it's also important to note that heavy use of heartburn medications that contain calcium carbonate can lead to buildup of unhealthily high levels of circulating calcium. For this reason it's important to take antacids like Tums only as recommended (via Popular Science). This is especially important for the 15 million Americans who experience daily heartburn (via The Washington Post).

Vitamin D and calcium

Our digestive systems aren't very good at absorbing calcium, and how much we absorb depends on the source of the calcium and how much we consume. We absorb about 30% of the calcium in dairy products and fortified foods. But calcium absorption from plant foods that are also high in oxalic acid and phytic acid is pretty abysmal — as low as just 5%. Caffeine can also decrease absorption. Ironically, the percentage of calcium you absorb from food or supplements decreases as the amount of calcium consumed increases (via the National Institutes of Health).

Fortunately, vitamin D improves the absorption of calcium. Vitamin D is a fat-soluble vitamin that can be obtained from a few foods (including fatty fish and fortified products like milk and cereal) and supplements. it can also be produced by the skin when it's exposed to sunlight. In the kidneys, vitamin D is converted into its active form, known as calcitriol. In addition to assisting with calcium absorption from the diet, calcitriol is needed by osteoblasts to produce new bone. Unfortunately, many Americans don't meet the recommended dietary allowance (RDA) for vitamin D of 15–20 mcg, depending on age. More than 20% of people in the United States are at risk of vitamin D insufficiency or deficiency, which also means they're less likely to be getting enough calcium (via the National Institutes of Health).

How calcium levels are controlled

Because it's a powerful electrolyte, circulating calcium levels are tightly controlled. The normal range for blood calcium is a narrow 8.5–10.2 mg/dL, although some labs may use slightly different ranges (via UCSF Health). The primary controllers of calcium balance are the parathyroid glands. These are four pea-sized organs that sit directly behind the much larger thyroid gland in the neck. When circulating levels of calcium are too low, the parathyroid glands release parathyroid hormone (PTH). PTH simultaneously triggers the bones to release calcium into the bloodstream, stops the kidneys from releasing calcium into the urine, and causes the kidneys to produce more of the active form of vitamin D to improve absorption of dietary calcium (via You and Your Hormones).

Calcium levels also appear to be influenced by calcitonin, a hormone made in the parafollicular cells (C-cells) of the thyroid gland. Calcitonin performs the opposite function of PTH, working to lower blood calcium levels. It does this by preventing the activity of osteoclasts, the bone cells responsible for breaking down bone to release calcium. Calcitonin also tells the kidneys to allow more calcium to leave the body via urine. But whether or not calcitonin is actually important remains up for debate, since both very high and very low levels of this hormone don't appear to negatively affect calcium levels in the blood (via You and Your Hormones).

When calcium levels are too high

Because circulating calcium levels are so tightly controlled, simply eating a ton of calcium-rich foods usually isn't enough to cause elevated blood levels. A too-high blood calcium level, known as hypercalcemia, is a relatively common condition. It can be the result of more than 25 diseases, certain medications, and dehydration. Hyperparathyroidism is the leading cause of hypercalcemia. In this condition, one or more of the parathyroid glands produce too much parathyroid hormone (PTH). These high levels of PTH cause too much calcium to leave the bones and enter the bloodstream. Lung, breast, and certain types of bone cancer can also cause dangerously high levels of circulating calcium, as can some diuretics, lithium, and the overuse of calcium carbonate antacids like Tums. Excessive intake of calcium, vitamin D, and vitamin A from supplements can also trigger hypercalcemia.

Hypercalcemia often doesn't cause symptoms. When symptoms do occur, they include frequent urination, fatigue, bone pain, muscle aches and cramps, GI upset, lethargy, depression, and changes in cognitive abilities. Treatment is aimed at addressing the underlying cause of the high calcium levels. Overactive parathyroid glands can be managed with medications or surgery, and problematic drugs can be stopped. If left untreated, however, hypercalcemia can eventually lead to brittle bones and fractures, kidney stones, kidney failure, high blood pressure, and slowed heart rate (via the Cleveland Clinic).

When calcium levels are too low

Circulating levels of calcium can also be too low — a condition known as hypocalcemia. According to the Merck Manual, hypocalcemia can have many causes. In some individuals, the parathyroid glands are either absent, damaged, or are underactive, meaning there isn't enough parathyroid hormone (PTH) to stimulate osteoclast cells to release calcium from the bones into the bloodstream. In some cases, individuals may have normal PTH levels, but their osteoclasts don't respond appropriately; this is known as pseudohypoparathyroidism. Insufficient magnesium intake can also lead to hypocalcemia because magnesium is needed to make PTH. Vitamin D deficiency, pancreatitis, and kidney dysfunction are also possible causes. Some medications, including certain antibiotics, anti-seizure drugs, and corticosteroids, can cause calcium levels to dip too low. And of course not eating enough calcium, as well as disorders that impair calcium absorption, can lead to hypocalcemia.

Hypocalcemia often doesn't cause any symptoms until it's moderately advanced. Low calcium levels can lead to dry skin, brittle nails, coarse hair, muscle cramps, memory loss, depression, and even hallucinations. If calcium levels get very low, individuals will experience tingling in their lips, tongue, fingers, and feet, as well as muscle aches, spams, and rigidity. Seizures and abnormal heart rhythms can also occur. Calcium supplementation (usually given intravenously and along with vitamin D) is often all that's required to reverse the symptoms of hypocalcemia. It's also important to treat the underlying cause. For example, synthetic PTH may be prescribed to combat underactive parathyroid glands.

Calcium and osteoporosis

Osteoporosis is a condition in which the bones become thin, weak, and prone to fractures. According to the National Osteoporosis Foundation, 10 million Americans have osteoporosis and another 44 million have osteopenia (low bone density). And if you think osteoporosis is something you don't need to worry about until you're much older, think again. As WebMD explained, bone thinning can happen at any age and often has no symptoms until the first broken bone.

Given the fact that calcium is so important for building strong bones, it makes sense that the more calcium you consume, the less likely you are to get osteoporosis. The research, however, is more mixed than you might think. In its analysis of past research, the National Institutes of Health (NIH) noted that some studies have shown a correlation between increased calcium intake and bone density, but in some cases these results are seen only in women. In other instances, no direct connection between the two factors could be found. The NIH also pointed out that "for the most part, the observational evidence does not show that increasing calcium intakes reduces the risk of fractures and falls in older adults." Despite sometimes contradictory research results, the Food and Drug Administration (FDA) allows manufacturers to make the health claim that use of calcium supplements reduces the risk of osteoporosis.

Calcium and cancer risk

According to the National Institutes of Health (NIH), most research doesn't support a link between increased calcium intake and decreased cancer incidence or mortality. The NIH noted, however, that one large clinical trial did find that cancer incidence from all causes was 60% lower in women who took calcium and vitamin D supplements and 47% lower in those who took calcium-only supplements. But when it comes to colorectal cancer specifically, most (but not all) research suggests that consuming more calcium decreases your risk. Calcium also appears to prevent the formation of adenomas, benign tumors that can morph into colon cancer. The NIH noted that "several observational studies have shown that the risk of prostate cancer might be higher with higher calcium intakes, but possibly only when the calcium comes from dairy foods." Research results are also mixed when it comes to the link between breast cancer and calcium intake.

According to the National Cancer Institute, almost 1.9 million new cases of cancer are diagnosed in the United States each year, and cancer remains one of the leading causes of death. There are roughly 149,000 new cases of colorectal cancer annually and almost 53,000 deaths. It's the third most commonly diagnosed cancer in both men and women and accounts for 9% of all cancer deaths in men and 8% of cancer deaths in women.

Calcium and heart disease

The Centers for Disease Control and Prevention (CDC) report that heart disease is the leading cause of death in the United States, claiming the lives of approximately 659,000 Americans each year. An estimated 805,000 people have heart attack annually. While high blood pressure, high cholesterol, smoking, diabetes, and obesity are all known risk factors for heart disease, what about calcium intake?

According to the National Institutes of Health (NIH), "calcium binds fatty acids, so it can reduce lipid [fat] absorption and might therefore lower [heart disease] risk." Many studies have indeed found a link between consuming less calcium and greater risk for high blood pressure and atherosclerosis (hardening of the arteries). In fact, those who consume more than 2,100 mg of calcium daily are 27% less likely to have atherosclerosis than those who consume around 300 mg daily, according to one study. However, it doesn't appear that calcium has any impact on the likelihood of having a heart attack or dying from heart disease. Some research has even suggested that long-term use of calcium supplements may increase heart disease risk by 15%. So what's the verdict? The NIH noted that "an expert panel convened by the National Osteoporosis Foundation and American Society for Preventive Cardiology determined ... that calcium intakes with or without vitamin D from foods or supplements neither increase nor decrease the risk of [heart disease] or [heart disease] mortality."