A Search for Optimally Bioavailable Calcium-Magnesium Supplement with Reduced Cardiovascular Risk
The patients will undergo a single dose bioavailability study in a randomized four-phase crossover design, comprised of 2% milk, effCaMgCit, calcium carbonate and placebo. The order of the four phases will be randomized.
in the 2% Milk Phase, fresh 2% milk containing 400 mg calcium (expected to be about 400 ml) will be ingested. in the effCaMgCit Phase, effervescent calcium magnesium citrate (containing 400 mg calcium, 122 mg magnesium and 50 meq citrate) in a sachet will be dissolved in the same volume (as 2% milk) of deionized-filtered water, and drunk as a single load. in the Calcium Carbonate Phase, calcium carbonate containing 400 mg calcium will be suspended in the same volume of deionized-filtered water and drunk. in the Placebo phase, microcrystalline cellulose will be suspended in the same volume of deionized-filtered water and drunk as a single load.
aim 1: To compare calcium and magnesium bioavailability of effCaMgCit versus two other calcium preparations and placebo in 24 healthy adult women. Calcium bioavailability will be measured from the calcemic response (rise in serum calcium concentration) over 6 hours after a single oral dose of effCaMgCit, 2% milk or calcium carbonate, containing the same amount of calcium (400 mg Ca). Magnesium bioavailability will be measured from magnesiuric (rise in urinary magnesium) as well as magnesemic response.
aim 2: To compare pharmacodynamic effects of effCaMgCit versus 2% milk, calcium carbonate and placebo from the reduction in serum PTH concentration after the test load.
aim 3. Following the test loads, to follow the time course of serum citrate, magnesium, ultrafiltrable calcium, ionized calcium, calcium complexes, and activity product of Ca2+ and HPo42- (as a measure of solubility with respect to a precursor phase of bone mineral and calcified tissues).
Healthy pre-menopausal women (age >= 21 years) and healthy postmenopausal women will participate in this randomized four-phase crossover study. They will be of any ethnicity. It is expected that all will be able to complete the study. Exogenous estrogen and selective estrogen receptor modulators will be allowed.