Overall, D(3) is slightly, but significantly, more effective than D(2) to increase serum 25(OH)D. One year of D(2) or D(3) dosing (1,600 IU daily or 50,000 IU monthly) does not produce toxicity, and 25(OH)D levels of less than 30 ng/ml persist in approximately 20% of individuals. Substantial between-individual response to administered vitamin D(2) or D(3) is observed.
Background: Subclinical vitamin K insufficiency, manifested by under-␥-carboxylation of the bone matrix protein osteocalcin, may be common. Objective: Our objective was to delineate the prevalence of submaximal ␥-carboxylation as assessed by response to phylloquinone supplementation and to evaluate the effect of this intervention on skeletal turnover in healthy North American adults. Design: Healthy subjects (n = 219), approximately equally distributed by sex and age (18-30 y and ≥ 65 y), received daily phylloquinone (1000 g) or placebo for 2 wk. Serum undercarboxylated osteocalcin (ucOC) and total osteocalcin, N-telopeptides of type I collagen (NTx), bone-specific alkaline phosphatase (BSAP), and phylloquinone concentrations were measured at baseline and after weeks 1 and 2. Results: At baseline, the mean serum phylloquinone concentration was lower in the young than in the old group; there was no effect of sex. Concomitantly, baseline %ucOC was highest in the young and lowest in the old men (P < 0.0001) but did not differ significantly by age in women. After supplementation, serum phylloquinone concentration increased Ϸ10-fold (P < 0.0001) at week 1 (from 0.93 ± 0.08 to 8.86 ± 0.70 nmol/L, x -± SEM); this was sustained through week 2. Among all supplemented groups, mean %ucOC decreased from 7.6% to 3.4% without significant differences by age or sex; 102 of 112 subjects had a > 1% decrease.
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