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In order for humans to absorb calcium, we need a special vitamin = Vitamin D. Without the vitamin D, we can drink as much milk, or take as many supplements of calcium as we want - we won't be able to use it!
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Calcium isn't just used for making strong bones! It is used to make cement, cheese, removing nonmetal from different metal mixes (called alloys), and also is used as an agent in the preparation of other metals.
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Pure calcium is actually a metal, and reacts very strongly, sometimes violently (explosively) with water and acids.
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Calcium has been known for thousands of years. The name calcium comes from the latin word "calcis" which means "lime." The romans were known to make "lime" from calcium oxide, brought from mines.
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Even though calcium has been known for thousands of years, it wasn't purified and identified as an element until 1808 by Sir Humphrey Davy of England.
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The best sources of calcium in the diet are milk, yogurt, and cheese. Nearly 72% of the calcium in the US comes from dairy foods.
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Some other foods also have a good amount of calcium, especially calcium fortified foods. These include calcium-fortified orange juice, tofu with calcium, collard greens, white beans, almonds, bok choy, rhubarb, red beans, and broccoli.
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Cows in the US can give an average of 6 ½ gallons of milk per day. This means that every cow can give over 100 glasses of milk per day!
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Calcium plays a big role in making muscles contract, helps to send messages through nerves, and also acts in the release of hormones. If calcium levels are low, the body will steal calcium from the bones to make up the difference.
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Calcium makes up the hard outer structure of bones in the human body, and gives them their strength. The inside of bones is very spongy, and full of holes, which makes bones very light.
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In humans, the glands responsible for regulating calcium are called parathyroid glands, and they are located around the thyroid gland in the neck. The parathyroid glands are so good at regulating calcium in the blood, the level of calcium usually only varies by 1-2%!
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Although the largest place to find calcium in the body is in bones, it is also found in cartilage - the softer connective tissue located between different joints, the ear, nose, and the rib cage.
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The reason doctors can take pictures of bones is because of the calcium. Calcium doesn't let certain energy, called x-rays, through them, and so appear bright white on film.
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