Overnight suppression of parathyroid hormone and bone resorption markers by active absorbable algae calcium. A...

In order to study the effect of Ca supplementation on the nocturnal rise of PTH and bone resorption, a double-blind, placebo-controlled study was carried out on 9 healthy male volunteers. Regimen A consisted of an oral dose of 150 mg Ca as AAACa after each meal and 450 mg at bedtime; B consisted of 300 mg after each meal and C was placebo. Plasma ionized Ca was significantly higher in A than in B at 6 a.m. the next morning and urinary Ca/Cr after 5 days was higher in A than in B and C. Plasma intact PTH fell by 19 +/- 4 pg/ml in A, 8 +/- 7 in B, and 1 +/- 7 after 1 day, and significantly decreased by 29 +/- 8 in A, increased by 11 +/- 11 in B, and 5 +/- 7 in C after 5 days (A and B, and A and C, p = 0.0242 and 0.0433, respectively), with increases of % tubular reabsorption of phosphorus. Urinary excretion of cross-linked collagen degradation product (Crosslaps) was 40 +/- 10% of the baseline in A, 97 +/- 22 in B, and 173 +/- 30 in C (A and C, P = 0.0061) after 5 days. Systolic blood pressure at 6 a.m. fell by 17 +/- 4 mmHg A, 24 +/- 3 in B, and 4 +/- 2 in C. Highly biologically available AAACa effectively suppressed nocturnal rise of PTH and bone resorption markers in 5 days.