What Is Calcium?
Calcium is a chemical element, number 20 on the periodic table. This mineral is considered a metal. We get most of our dietary calcium not in its free form, but in compounds with other molecules. This makes the calcium more stable, allowing the body to digest the compound and free calcium for use in a variety of physiological processes.

Physiological Role of Calcium in the Body
Calcium plays a major role in bone health, with calcium and phosphorus representing the primary minerals that lend bones strength (Weaver, 2016). Calcium is also important for nerve impulse transmission, as an influx of cellular calcium is needed for individual neurons to release their signalling molecules to make contact with nearby cells. Calcium also helps to mediate the constriction and relaxation of blood vessels, secretion of hormones, muscle contraction, and enzymatic reactions needed for cell metabolism.

Health Benefits of Getting Enough Calcium
Decades of research supports the use of calcium to improve health outcomes for individuals at risk for certain conditions. For instance, osteoporosis is a condition characterized by increased bone brittleness and loss of bone strength. Getting enough calcium can reduce your risk of osteoporosis (Office of Dietary Supplements, 2016). This is particularly important for postmenopausal women, as hormonal changes can negatively impact bone health.

Getting enough calcium may also reduce your risk of developing kidney stones, particularly when taken with vitamin D (Weaver, 2014). Calcium is also associated with lower risk of hypertension during pregnancy, colorectal cancer, and lead toxicity among children. Furthermore, some scientific evidence suggests that increasing dietary calcium can promote healthy weight loss in overweight or obese individuals. Calcium may also lower your risk of hypertension, which is associated with your overall cardiovascular risk. This variety of beneficial effects from calcium speaks to the important role the mineral plays in dozens of metabolic processes.

Recommended Daily Intake of Calcium
The Institute of Medicine has established a recommended daily allowance for calcium (Weaver, 2014). This sets forth the amount of calcium that regular people need to maintain good health. The recommended daily allowance depends on age. Adult men and women below age 50 need 1,000 mg of calcium per day. From age 51 to 70, men should continue to aim for 1,000 mg daily, while women need slightly more, at 1,200 mg per day. Men and women above age 71 should get 1,200 mg of calcium per day. The increasing recommended daily allowance of calcium for older adults is due to their increased risk for osteoporosis and other bone problems.

Unfortunately, many Americans do not meet their daily calcium target. Despite calcium being crucial for healthy development, just 23% of boys and 15% of girls between the age of 9 and 13 years meet the recommended daily allowance (Bailey et al., 2010). Adults aged 19 to 30 do not fare much better, with only two-thirds of men and one-third of women getting enough.

Foods that Are Good Sources of Calcium
Certain foods in the U.S. diet are fortified with calcium to help people get enough. For example, orange juice and breakfast cereals are typically fortified with calcium. Some natural sources of dietary calcium include:

Tofu (½ cup serving): 434 mg
Yogurt (1 cup): 415 mg
Sardines (1 cup): 325 mg
Milk (1 cup): 300 mg
Cheddar cheese (1.5 ounces): 303 mg
White beans (½ cup): 81 mg
Bok choy (½ cup): 79 mg
Figs (dried; ¼ cup): 61 mg
Orange (1 medium): 60 mg
Kale (½ cup, cooked): 47 mg
Calcium Deficiency Signs and Symptoms
Severe calcium deficiency tends to be quite rare in the United States (Office of Dietary Supplements, 2016). This is because your body has one large source of calcium that is constantly available: the bones. When blood levels of calcium dip too low, your body can signal cells to break down bone tissue to make more calcium available. The opposite process occurs when there is excess calcium: it is deposited into bones to add strength and stability.

However, calcium deficiency can occur in some individuals, particularly those who have experienced kidney failure, removal of the stomach, or digestive disorders such as Crohn’s disease or ulcerative colitis. Taking certain medications can also inhibit calcium absorption, leading to calcium deficiency. The most common symptoms of calcium deficiency include (Office of Dietary Supplements, 2016):

Poor appetite
Altered heart rhythms
Numbness or tingling in the extremities
Muscle cramping
In severe cases, calcium deficiency can even cause death.

Other Considerations for Calcium Intake
Eating foods rich in calcium may not be enough to meet your recommended daily allowance if the type of calcium you receive is not bioavailable. The bioavailability of a mineral refers to your body’s ability to use the nutrient from a food. For example, the compound oxalic acid (sometimes called oxalate) can inhibit calcium absorption (Weaver, 2014). Oxalic acid is found in spinach, rhubarb, dried beans, and sweet potatoes. Thus, when attempting to increase your intake of the mineral, it may help to avoid these foods when eating other calcium-rich foods.

In contrast, calcium-rich foods such as broccoli, cabbage, turnip greens, and kale contain a form of calcium that is just as available as the calcium found in milk. This makes cruciferous vegetables an important source of dietary calcium for vegans. Additionally, the presence of vitamin D may increase your body’s ability to absorb calcium (Weaver, 2014). Thus, foods that are rich in both vitamin D and calcium (e.g., milk) are excellent ways to reach your recommended daily allowance.

Calcium supplements are available for individuals who cannot get enough of this important mineral through their diet. However, nutrition experts recommend that you try to reach your recommended daily allowance of calcium through your regular diet (Office of Dietary Supplements, 2016). This is because dietary calcium may be more bioavailable and may work better than supplements.

If you do choose to take a calcium supplement, there are two broad classes: carbonate and citrate (Office of Dietary Supplements, 2016). Calcium carbonate is inexpensive and more commonly available. However, it is absorbed more efficiently with food, while calcium citrate can be taken with or without food. This makes calcium citrate a better course for individuals with digestive disorders or other problems that prevent them from properly absorbing calcium from their food.

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