Calcium Absorption from supplement tablets is correlated with how well the calcium tablet disintegrates. Disintegration is important because a tablet must disintegrate before it can be absorbed. Since calcium absorption is most rapid in the upper small intestine, a significant delay in the release of Calcium from a poorly disintegrating supplement will reduce the amount of Calcium absorbed. In studies testing the disintegration of calcium tablets, a single tablet is placed in an erlenmeyer flask containing 150 ml vinegar at room temperature and swirled vigorously every 5 minutes until disintegration is observed. The test is repeated four times per brand of tablet. Disintegration in vinegar has been reported in one study to range from 2.8 minutes to greater than 180 minutes (1). Other studies have reported disintegration times of various calcium products in vinegar ranging from 1.8 minutes to greater than 30 minutes and disintegration time in distilled water ranging from 1.6 minutes to greater than 60 minutes (2). Patients can easily test their own brand of supplements at home using a similar procedure.
Postmenopausal women often suffer from achlorhydria which inhibits the absorption of calcium salts under fasting conditions. These women or others suffering from decreased stomach acid production, may benefit from supplementation with an acidified form of calcium, or from taking calcium supplements with light meals, which will improve absorption (3). In achlorhydric subjects, calcium citrate is ten times as well absorped as is calcium carbonate (3).
1.: Whiting SJ; Pluhator MM.
Comparison of in vitro and in vivo tests for determination of availability of calcium from calcium
carbonate tablets.
Journal: Journal of the American College of Nutrition, 1992 Oct, 11(5):553-60.
Unique ID: 93085093.
In vitro tests of calcium (Ca) availability and the oral Ca load test were conducted on eight brands
of calcium carbonate (CaCO3) tablets each providing 500 mg Ca. Disintegration time measured using
USP criteria or with the vinegar test can be used to distinguish poorly available tablets from
acceptable tablets.
2.Mason NA; Patel JD; Dressman JB; Shimp LA.
Consumer vinegar test for determining calcium disintegration.
American Journal of Hospital Pharmacy, 1992 Sep, 49(9):2218-22.
Unique ID: 92397896.
The mean disintegration times of various calcium products in vinegar ranged from 1.8 to greater than 30
minutes. The mean time in distilled water ranged from 1.6 to greater than 60 minutes. Results were in
agreement in 87% to 93% of cases between the consumer vinegar test and the standardized disintegration test
methods, a significant correlation. No correlation was found between disintegration time and the extent of
dissolution.
3 Recker RR.
Calcium absorption and achlorhydria.
New England Journal of Medicine, 1985 Jul 11, 313(2):70-3.
(UI: 85213784)
Defective absorption of calcium has been thought to exist in patients with achlorhydria. Absorption of calcium
was compared in its carbonate form with that in a pH-adjusted citrate form in a group of 11 fasting patients
with achlorhydria and in 9 fasting normal subjects. Absorption of calcium from carbonate in patients
with achlorhydria was significantly lower than in the normal subjects and was lower than absorption
from citrate in either group; absorption from citrate in those with achlorhydria was significantly
higher than in the normal subjects, as well as higher than absorption from carbonate in either
group. Administration of calcium carbonate as part of a normal breakfast resulted in completely normal
absorption in the achlorhydric subjects. These results indicate that calcium absorption from carbonate is
impaired in achlorhydria under fasting conditions. Since achlorhydria is common in older persons, calcium
carbonate may not be the ideal dietary supplement.