Why Do We Need Calcium?
The primary role of calcium is to help build bones and teeth and keep them strong. It's also needed for muscle contraction, heartbeat, nerve function, and blood clotting. Because bone is living tissue, calcium gets deposited and withdrawn daily. Small amounts are withdrawn from the bones to be used for other functions in the body, and that calcium needs to be replaced in order to avoid bone loss.
How Much Do I Need?
The rate at which calcium is deposited and resorbed varies with age, so calcium requirements also vary with age. For growing children, bone formation exceeds resorption, whereas in early and middle adulthood both processes are relatively equal. In aging adults, particularly among postmenopausal women, bone breakdown exceeds formation, resulting in bone loss and an increased risk of osteoporosis.
Here's a breakdown of recommended daily calcium intakes for different ages:
Birth–6 months: 210 mg
7–12 months: 270 mg
1–3 years: 500 mg
4–8 years: 800 mg
9–18 years: 1,300 mg
19–50 years: 1,000 mg
50+ years: 1,200 mg
Calcium requirements for women who are pregnant or breastfeeding are the same as for other women in that age group.
Where Do I Get Calcium?
The major food sources of calcium are milk, yogurt, and cheese. Non-dairy sources include some leafy green vegetables such as kale, broccoli, and bok choy, fish with edible bones, calcium-fortified soy beverages, and tofu made with calcium sulfate. A number of other foods such as fruit juices and drinks, tofu, and cereals are fortified with calcium. You can also get calcium in dietary supplements and antacid medications containing calcium carbonate.
Absorption of Calcium
In order to be absorbed adequately, calcium needs its partner, vitamin D. Foods that contain phytic acid (whole-grain products, wheat bran, seeds, nuts, soy isolates) or oxalic acid (spinach, collard greens, sweet potatoes, rhubarb, beans) can affect calcium absorption because those acids bind with the calcium and inhibit absorption. Caffeine and alcohol have also been shown to reduce calcium absorption.
Although severe calcium deficiencies are rare in the U.S., there are a few groups who tend to be at risk for sub-optimal intakes: postmenopausal women, amenorrheic women, female athletes with amenorrhea, eating disorders, and osteoporosis, individuals with lactose intolerance, and vegetarians.
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