Overnight suppression of parathyroid hormone and bone resorption markers by active absorbable algae calcium. A double-blind crossover study

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.