Calcium is the most abundant mineral in the body. About 99% of this essential nutrient is contained in bones and teeth with the rest being in blood and other tissues. Calcium is needed for strong bones and teeth and for nerve conduction, muscle contraction, heart muscle function, blood pressure regulation, glycogen to glucose conversion, initiation of blood clotting, many hormone actions, many enzyme activities and making acetylcholine, an important chemical for nerve transmission. Calcium plays a part in the prevention of colon cancer.
Most importantly, calcium opposes phosphorus as a buffer to maintain the acid-alkaline balance of the blood and is critical for milk production in the nursing of infants.
Calcium absorption in the small intestine is complex and has specific requirements.
1. Ionization. Calcium atoms dissolved from food in stomach juices must be ionized, that is, the atoms must become positively charged to be absorbed and to be useful to body processes that require this mineral. This action requires that the stomach juice is sufficiently acidic so that ionization will happen.
2. Absorption. Calcium ions can be absorbed from the small intestine into the bloodstream by two mechanism: active transport and/or passive transfer.
- Active transport. This mechanism is especially important when the amount of calcium in food eaten is low and when the need for more calcium is not being met. Ionized calcium is rapidly absorbed by active transport through the lining of the first part of the duodenum where the juice is still acidic as it enters from the stomach. In the duodenum, active transport of calcium into the bloodstream is controlled through the complex action of vitamin D in its active hormonal form, vitamin D3. Vitamin D3 stimulates the production of proteins called calbindins to specifically bind calcium for transport.
- Passive transfer. In the remainder of the small intestine, where the intestinal juice is normally highly alkaline, absorption of calcium ions by passive transfer is slower, providing there is adequate absorptive surface. Most calcium is passively absorbed in the ileum section of the small intestine.
In untreated celiac disease, deficiency of calcium commonly results from either malabsorption of calcium alone or calcium malabsorption combined with vitamin D deficiency. It is often worsened by a calcium poor diet.
1. Lost calcium in the small intestine.
- Ionized calcium is made unabsorbable by binding with free (unabsorbed) fatty acids in the small intestine. That is, calcium binds with fat to form soap. The resulting calcium-laden soap passes into the colon for excretion.
- Absorptive surface area of the intestinal lining is inadequate. There is not enough functional surface area to absorb the calcium the body needs.
- Vitamin D regulated proteins needed for active transport is too low.
2. Poor use of calcium in the body. Blood albumin (protein) level is too low.
Calcium deficiency in celiacs on the gluten-free diet treatment correlates with the general population. Some important factors leading to calcium deficiency on the gluten-free diet are:
- Not enough calcium in the diet.
- Not enough vitamin D in the diet or skin exposure to sunshine (a major source of vitamin D).
- Diet too high in oxalic acid. Ionized calcium (activated) is made unabsorbable in the small intestine by binding with oxalic acid (found in food such as spinach, beet greens, rhubarb). The resulting calcium-oxalic acid complex passes into the colon for excretion, thus losing the calcium in stool.
- Diet too high in phytic acid. Ionized calcium is made unabsorbable in the small intestine by binding with phytic acid (found in husks of whole grains). The resulting calcium-phytate complex passes into the colon for excretion, thus losing calcium in stool.
- Diet too high in fiber. More than 30 grams of fiber interferes with calciumn absorption.
Calcium deficiency impairs the ability of muscles to contract, nerves to conduct impulses and blood vessels to regulate blood pressure. Osteoporosis develops as bone gives up its calcium to provide for essential functions. Inadequate calcium, stemming from vitamin D deficiency, contributes to osteomalacia in adults and rickets in children. Osteomalacia/rickets result in softening of bones and deformity shown by bowing of the legs and flattening of the pelvis. Finally, low calcium is shown to be involved in colon cancer.
Symptoms of mild to moderate depletion:
- muscle spasms/cramps
- excessive bleeding
- changes in saliva composition
- periodontal disease
- bone pain
If the level of calcium in the blood drops significantly (hypocalcemia), tetany, convulsions, and laryngospasm can develop. These dramatic symptoms involve severe muscle spasms that may be life-threatening. In prolonged deficiency, cataracts develop.
In pregnancy, pre-eclampsia develops (hypertension, protein spilling in urine, and swelling). Pre-eclampsia marked by sudden weight gain, headaches and visual disturbances can rapidly advance to eclampsia with potential loss of the baby and mother.
Food Sources of Calcium
Calcium deficiency responds to a gluten-free diet rich in calcium. Calcium is found in both animal and plant foods. Below are some important food sources.
milk and milk products such as yogurt
sesame seeds, chia seeds
fortified orange juice
green, leafy vegetables: collards, turnip
greens, mustard green, dandelion
Recommended Dietary Allowances for Calcium
People whose bone density scan shows decreased axial bone density should obtain 1,200 mg calcium and 400 mg vitamin D daily.
Getting Your Daily Intake
Make strong bones a priority! If you are irritable, have muscle cramps, or can’t sleep, act now to add calcium-rich foods to your diet. This is especially important if you have a sedentary lifestyle. With enough calcium, you can become more rested, lower your blood pressure and gain a better frame of mind.
- Eat more fresh, green leafy vegetables.
- Freely season meals with calcium-rich basil, marjorum, thyme, dill, sage, spearmint, parsley, chervil, celery seed, rosemary, coriander, cinnamon, fennel and tarragon.
- Choose decaffeinated coffee and tea.
- Give up soda now! Soda acts to deplete the body of calcium.
Form in Dietary Supplements
Calcium citrate is the best choice, especially if you have low acid in your stomach. Calcium carbonate does not dissolve as well and is actually used as an antacid – in Tums for example. Be aware that bone meal and dolomite may contain lead as a contaminant.
Excessive supplemental intake is not without risk. It may cause constipation, interfere with the absorption of other minerals such as iron, magnesium and manganese, and cause kidney stones. 2,000 mg of calcium in the presence of a high level of vitamin D is a potential cause of hypercalcemia, leading to excessive calcification in soft tissues, such as the kidneys, which may be life-threatening.
Impact of Storage, Processing, and Cooking
Calcium is minimally affected by storage, processing or cooking.
Author Information: Cleo Libonati, RN, BSN
Cleo Libonati is president/CEO and co-Founder of Gluten Free Works, Inc. She is the author of Recognizing Celiac Disease and the Gluten Free Works Health Guide.