Vitamin D is Needed
Calcium is regulated by vitamin D that helps your body absorb the calcium and place it in your bones. It is also controlled by calcitonin that helps your bones store calcium, and by the parathyroid hormone that regulates the transfer of calcium from the bones to the blood. With a lack of vitamin D, less than 10% of dietary calcium can be absorbed.
Calcium, Lead, Aluminum and Nutritients
Calcium in the intestines blocks lead absorption. Aluminum containing antacids can inhibit calcium absorption. Too much calcium can interfere with the absorption of copper, iron, magnesium, manganese and zinc.
Calcium, Magnesium, Potassium, Phosphorus
High levels of calcium, magnesium or potassium can produce low levels of the other. Calcium and phosphorus work together to create healthy bones and teeth. If phosphorus intake is too high, your body gets rid of the extra and calcium with it.
Calcium, Sugar, Antibiotics, Iron and Aspirin
Large amounts of sucrose can increase calcium excretion. Sugars and phosphoric acid are the main ingredients in soft drinks. Calcium reduces the absorption of tetracycline antibiotic, iron and aspirin when taken at the same time.
Absorption and Calcium Deficiencies
Large amounts of fat, oxalic acid found in chocolate and rhubarb, and phytic acid found in grains can prevent calcium absorption. Contraceptive pills, anti-epileptic drugs, diuretics, corticosteroids for rheumatoid arthritis, asthma and IBD, and some antidepressants may create a calcium deficiency. A deficiency can be created by smoking, poor absorption due to lactose intolerance and absorption disorders such as coeliac disease.
Do not take calcium supplements if you have impaired kidney functions or history of kidney/bladder stones, or if you have constipation. Calcium may increase urinary excretion. It may increase the formation kidney stones.