Everyone needs adequate amounts of calcium to maintain healthy teeth and bones. Besides this, you also need this mineral for proper muscular contraction, ensuring normal enzyme function and blood clotting, and maintaining a regular heart rate. If your body fails to absorb and retain enough calcium, you may experience seizures, spasms, muscle aches and difficulty breathing. There are several possible causes for inadequate calcium absorption, such as the foods you eat, interactions with medicines, certain diseases, and vitamin D deficiency.

Interactions with Medication

Some prescription medications can inhibit the amount of calcium your body absorbs, the University of Maryland Medical Center reports. These include bile acid sequestrants such as colestipol, cholestyramine, and colesevelam, which lower your cholesterol but may also increase the amount of calcium excreted through urine.

Long-term use of corticosteroids may lead to low calcium and may have to be remedied through calcium supplementation. Anti-seizure medicines such as phenobarbital, phenytoin and primidone can also decrease calcium levels. To counteract this, some doctors recommend vitamin D supplements. Some diuretics also affect affect calcium: thiazide diuretics raise serum calcium, while loop diuretics have the opposite effect.

Vitamin D Deficiency

You cannot efficiently absorb and process calcium without enough vitamin D, the Linus Pauling Institute notes. Some foods contain vitamin D, such as fish, eggs, fortified milk and cod liver oil. Your body also manufactures it when your skin is exposed to ultraviolet rays from sunlight. Adults need between 400 to 600 IU of vitamin D, while children should get 200 IU. A vitamin D deficiency can result from not getting enough sunlight, maintaining a strict vegan or vegetarian diet, or not drinking enough milk. Without this critical nutrient, your calcium absorption is drastically lowered.

Diseases

Certain types of disease can disrupt calcium absorption and lead to low calcium levels, Merck Manual Home Edition notes 1. Renal disorders are among the most common causes. These conditions stop your kidneys from converting vitamin D-2 into its active form, vitamin D-3 or cholecalciferol, that is needed to process calcium. This prevents the normal absorption of calcium into your bones and causes calcium loss through urine. Pancreatitis, celiac disease, and inflammatory bowel disorders such as Crohn’s disease and ulcerative colitis can also prevent proper absorption of calcium from your food.

Phytic Acid and Oxalic Acid

Some types of foods are high in phytic acid or oxalic acid, two chemicals that bind to calcium and prevent it from being absorbed efficiently, the Office of Dietary Supplements explains 2. Oxalic acid is found primarily found in vegetables such as:

• chives
  
• parsley
  
• collard greens
  
• radishes
  
• spinach
  
• sweet potatoes
  
• celery
  
• beets
  
• rhubarb

The extent to which these two chemicals lower calcium absorption is variable; however, they may have a greater negative effect when these foods are consumed simultaneously with milk.