What affects Calcium absorption? Not all calcium consumed is actually absorbed in the gut. Humans absorb about 30% of the calcium in foods, but this varies depending upon the type of food consumed.[i]
- Calcium absorption depends on your body’s available calcium and on the total amount of elemental calcium consumed at one time
- Dosage: Absorption is highest in doses < 500 mg[i]. The efficiency of absorption decreases as calcium intake increases. Therefore, separate doses into twice or three times daily for optimal absorption. [ii]
- Age: As we get older, absorption efficiency decreases. In order word, there may be increase need of calcium.
- Vitamin D: many studies are now showing that many people are deficient in vitamin D
- Combining with food containing high level of phytic acid and oxalic acid: spinach, collard green, sweet potatoes, rhubarb, beans, whole grain products, wheat bran, beans, seeds, nuts and soy isolates. Phytic acid and oxalic acid bind to calcium and can inhibit its absorption.[iii] However, if one eat a variety of foods, these interactions probably have little or no nutritional consequence.
- Acidogenic diet: Metabolic acids produced by diets high in protein and cereal grains increase calcium excretion[iv], therefore it is thought to negatively affect calcium status.
Importance of vitamin K2 in Calcium:
The role of Vitamin K2 in calcium is binding calcium to the bone matrix after calcium is absorbed.
Calcium Deficiency: Although frank calcium deficiency is uncommon, inadequate intakes of dietary and supplemental calcium below recommended level would have negative health impact over the long term
- other symptoms may include muscle cramps, numbness and tingling in the fingers
- poor appetite, abnormal heart rhythms, poor teeth
- osteopenia (early stage of osteoporosis)
Groups at Risk of low Calcium
- Individuals with lactose sensitivity, intolerance or cow’s milk allergy
- Postmenopausal women
- Amenorrheic women: Amenorrhea, the condition in which menstrual periods stop or fail to initiate in women of childbearing age, results from reduced circulating estrogen levels that, in turn, have a negative effect on calcium balance.
Vegetarians might absorb less calcium because they consume more plant products containing oxalic and phytic acids and because of their avoidance of dairy foods[v],[vi]. In the Oxford cohort of the European Prospective Investigation into Cancer and Nutrition, bone fracture risk was similar in meat eaters, fish eaters and vegetarians, but higher in vegans, likely due to their lower mean calcium intake[vii].
Interactions with Medications
Calcium supplements have the potential to interact with several types of medications. Individuals taking these medications on a regular basis should discuss their calcium intake with their healthcare providers.
Calcium can decrease absorption of the following drugs when taken together: biphosphonates (to treat osteoporosis), the fluoroquinolone and tetracycline classes of antibiotics, levothyroxine, phenytoin (an anticonvulsant), and tiludronate disodium (to treat Paget’s disease)[viii],[ix],[x]
Thiazide-type diuretics can interact with calcium carbonate and vitamin D supplements, increasing the risks of hypercalcemia and hypercalciuria. [xi]
Both aluminum- and magnesium-containing antacids increase urinary calcium excretion. Mineral oil and stimulant laxatives decrease calcium absorption. Glucocorticoids, such as prednisone, can cause calcium depletion and eventually osteoporosis when they are used for months. [xi]
[i] Committee to Review Dietary Reference Intakes for Vitamin D and Calcium, Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
[iii] Weaver CM, Heaney RP. Isotopic exchange of ingested calcium between labeled sources: evidence that ingested calcium does not form a common absorptive pool. Calcif Tissue Int 1991;49:244-7. [PubMed abstract]
[iv] Fenton TR, Eliasziw M, Lyon AW, Tough SC, Hanley DA. Meta-analysis of the quantity of calcium excretion associated with the net acid excretion of the modern diet under the acid-ash diet hypothesis. Am J Clin Nutr. 2008 Oct;88(4):1159-66. [PubMed abstract]
[viii] Shannon MT, Wilson BA, Stang CL. Health Professionals Drug Guide. Stamford, CT: Appleton and Lange, 2000.
[ix] Jellin JM, Gregory P, Batz F, Hitchens K. Pharmacist’s Letter/Prescriber’s Letter Natural Medicines Comprehensive Database. 3rd ed. Stockton, CA: Therapeutic Research Facility, 2000.
[xii] Jellin JM, Gregory P, Batz F, Hitchens K. Pharmacist’s Letter/Prescriber’s Letter Natural Medicines Comprehensive Database. 3rd ed. Stockton, CA: Therapeutic Research Facility, 2000.