Calcium is the most abundant mineral in the body. It is well known for its key role in maintaining strong teeth and bones. The teeth and bones contain 99 percent of the calcium in the body. The remaining 1% is found in the body's fluids and cells. The body needs vitamin D in order to absorb calcium. Calcium works closely with magnesium, zinc, fluoride, and phosphorus. It also helps to maintain proper heart function, nerve transmission, and blood clotting. Complex processes control the amount of calcium in the blood. When there is too little of it in the blood, hormones pull it from the bones to meet the body's demands.
What food source is the nutrient found in?
Non-fat dairy products are one of the best sources for calcium. Dark green leafy vegetables and fish with edible bones, such as salmon, are also good sources. Many breakfast cereals and orange juice brands have added calcium.
Some foods can interfere with the absorption calcium. Foods that may do this include:
- vegetables, such as spinach
- some grains
High protein intake can also interfere with the body's uptake of calcium.
Sources of calcium include:
- milk, skim = 300 milligrams (mg) per cup
- yogurt = 345 to 450 mg per cup
- mozzarella cheese = 200 mg per ounce
- tofu = 130 mg per half cup
- calcium-fortified orange juice = 225 mg per 3/4 cup
- mustard greens = 50 mg per half cup
- broccoli = 45 mg per half cup
- canned fish, 3 ounces of salmon (with bones) = 195 mg, 3 ounces of sardines (with bones) = 370 mg
How does the nutrient affect the body?
The most well known function of calcium is to preserve bone density. This process is aided by other key vitamins and minerals including magnesium and vitamin D.
Without enough calcium, bones may lose density. This condition is called osteopenia (mild loss of bone density) or osteoporosis (more severe loss of bone density).
More than 25 million Americans, mostly women, suffer from osteoporosis. This disease puts people at greater risk for hip and other bone fractures.
Bones act as a reservoir for calcium. If there is not enough calcium circulating in the blood to meet the body's needs for the mineral, it will be pulled from the bones.
Typically, people keep building up calcium in the bones through their late 20's and early 30's. After age 30 to 35, bones begin to naturally lose minerals such as calcium that give them strength.
After age 50, calcium loss from bone becomes even more common, especially among women. The hormone estrogen helps keep calcium in bones. After menopause, a woman's body stops producing estrogen. This increases the loss of calcium from bone .
Hormone replacement therapy and weight-bearing exercise such as walking and weight lifting can help maintain bone density in post-menopausal women.
If people get enough calcium in their youth, they can build a healthy reservoir to draw from in later years. Later in life, a person needs to consume enough calcium so that it is not robbed from the bones. Vitamin D also helps the body to absorb calcium into the bones.
Bone health is not the only function of calcium in the body. Calcium is also needed for vital nerve and muscle transmission including the healthy function of the heart. Several recent studies have shown how calcium can help lessen both the physical and emotional symptoms of pre-menstrual syndrome, which is also known as PMS. The mechanism behind this effect is not yet known. It may be because of calcium's close link with certain hormones. The dose used in these studies was 1200 mg a day.
The Institute of Medicine recommends the following amounts of calcium:
The quotas for some age groups were raised from earlier levels. This action was in response to new knowledge about calcium's role in the prevention of osteoporosis.
It's estimated that the average adult gets only 500 to 700 mg of calcium daily. The goal for all people should be to get the recommended amount of calcium each day. However, calcium intake should not exceed 2,500 mg per day. Getting too much calcium can cause harmful deposits in the kidneys and heart. High intake can also reduce the absorption of zinc and iron; impair vitamin K metabolism, and encourage the loss of calcium from the bones.
There are many supplements on the market for people who have a hard time getting enough calcium through diet alone. To be stable and absorbable, calcium in supplements is always paired with another compound.
Calcium citrate and calcium citrate-malate are usually the best absorbed by older adults.
Calcium carbonate, the type of calcium common in antacids, is more concentrated. It often costs less than other compounds.
It is wise to avoid supplements with oyster shell, dolomite or bone meal because they may also contain small amounts of lead, which can be very harmful.
Calcium supplements should be taken with meals to help the body absorb them. They should not be taken at the same time as iron supplements, because calcium blocks the absorption of iron.
If a person needs more than one tablet per day, the extra pills should be spread out through the day and not taken all at one time.
One should drink plenty of fluids with calcium supplements to avoid constipation. Taking a calcium supplement with milk can help enhance absorption because of the lactose and vitamin D in milk.
Calcium supplements should not be used as a substitute for healthy food choices. They should only be used to supplement the diet. To increase calcium from foods in the diet, individuals can:
- include yogurt with breakfast
- drink a glass of milk with each meal
- use milk in coffee or tea instead of creamer
- add low-fat cheese to sandwiches or salads
- check food labels for calcium content
- add tofu to casseroles
- drink orange juice fortified with calcium for breakfast or as a snack
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Duyff, R., MS, RD, CFCS. (1996). The American Dietetic Association's Complete Food&Nutrition Guide. Minnesota: Chronimed Publishing.