Calcium ：How does it work and Are there safety concerns?

How does it work?
The bones and teeth contain over 99% of the calcium in the human body. Calcium is also found in the blood, muscles, and other tissue. Calcium in the bones can be used as a reserve that can be released into the body as needed. The concentration of calcium in the body tends to decline as we age because it is released from the body through sweat, skin cells, and waste. In addition, as women age, absorption of calcium tends to decline due to reduced estrogen levels. Calcium absorption can vary depending on race, gender, and age.
Bones are always breaking down and rebuilding, and calcium is needed for this process. Taking extra calcium helps the bones rebuild properly and stay strong.
Are there safety concerns?
Calcium is LIKELY SAFE for most people when taken appropriately in recommended doses. Calcium can cause some minor side effects such as belching or gas.
Avoid taking too much calcium. The Institute of Medicine sets the daily tolerable upper intake level (UL) for calcium based on age as follows: Age 0-6 months, 1000 mg; 6-12 months, 1500 mg; 1-3 years, 2500 mg; 9-18 years, 3000 mg; 19-50 years, 2500 mg; 51+ years, 2000 mg. Higher doses increase the chance of having serious side effects. Some recent research also suggests that doses over the recommended daily requirement of 1000-1300 mg daily for most adults might increase the chance of heart attack. This research is concerning, but it is still too soon to say for certain that calcium is truly the cause of heart attack. Until more is known, continue consuming adequate amounts of calcium to meet daily requirements, but not excessive amounts of calcium. Be sure to consider total calcium intake from both dietary and supplemental sources and try not to exceed 1000-1300 mg of calcium per day. To figure out dietary calcium, count 300 mg/day from non-dairy foods plus 300 mg/cup of milk or fortified orange juice.
Special Precautions & Warnings:
Pregnancy and breast-feeding: Calcium is LIKELY SAFE when used in recommended amounts during pregnancy and breast-feeding.
High levels of phosphate in the blood (hyperphosphatemia) or low levels of phosphate in the blood (hypophosphatemia): Calcium and phosphate have to be in balance in the body. Taking too much calcium can throw this balance off and cause harm. Don’t take extra calcium without your health provider’s supervision.
Under-active thyroid (hypothyroidism): Calcium can interfere with thyroid hormone replacement treatment. Separate calcium and thyroid medications by at least 4 hours.
Too much calcium in the blood (as in parathyroid gland disorders and sarcoidosis): Calcium should be avoided if you have one of these conditions.
Are there any interactions with Herbs and Supplements?
Magnesium
Calcium supplements can decrease the absorption of dietary magnesium, but only at very high doses (2600 mg per day). However, in people who have enough magnesium stored in their bodies, taking calcium doesn’t cause a problem over the long term. People at high risk for magnesium deficiency, however, should take calcium supplements at bedtime, instead of with meals, to avoid reducing dietary magnesium absorption.
Vitamin D
Taking vitamin D along with calcium increases absorption of calcium.
Are there interactions with Foods?
Caffeine
High caffeine intake from foods and beverages causes the body to remove calcium. Taking more than 300 mg of caffeine per day (three to four cups of coffee, or six 12-oz. cola drinks) is linked to increased bone loss and breaks in elderly women, especially when calcium intake is low. Be sure to get the amount of calcium from food and supplements that is recommended for your age and gender.
Fiber
Dietary fiber from certain sources can interfere with calcium absorption. These sources include wheat bran, spinach, rhubarb, and others. It’s best not to eat fibrous foods within two hours of taking calcium supplements.
Iron
Calcium supplements may decrease the absorption of dietary iron. However, in people who have enough iron stored in their body, taking calcium doesn’t cause a problem over the long term. People who are at high risk for iron deficiency should take calcium supplements at bedtime, instead of with meals, to avoid reducing the absorption of iron.
Magnesium
Calcium supplements may decrease the absorption of dietary magnesium. However, in people who have enough magnesium stored in their body, taking calcium doesn’t cause a problem over the long term. People who are at high risk for magnesium deficiency should take calcium supplements at bedtime, instead of with meals, to avoid reducing the absorption of magnesium.
Sodium
Eating foods that contain a lot of sodium causes the body to remove calcium. A calcium intake of 1000 mg/day is needed to prevent bone loss in postmenopausal women ingesting 2000 mg sodium chloride daily. About 1500 mg/day calcium is needed if sodium chloride intake is 3000 mg/day.
Zinc
Calcium supplements may decrease the absorption of dietary zinc. However, in people who have enough zinc stored in their body, taking calcium doesn’t cause a problem over the long term. People who are at high risk for zinc deficiency should take calcium supplements at bedtime, instead of with meals, to avoid reducing the absorption of zinc.