Vitamin K supplementation reduces serum concentrations of under-gamma-carboxylated osteocalcin in healthy young and elderly adults

Background: Subclinical vitamin K insufficiency, manifested by under-gamma -carboxylation of the bone matrix protein osteocalcin, may be common. Objective: Our objective was to delineate the prevalence of submaximal gamm a -carboxylation as assessed by response to phylloquinone supplementation a nd to evaluate the effect of this intervention on skeletal turnover in heal thy North American adults. Design: Healthy subjects (n = 219), approximately equally distributed by se x and age (18-30 y and greater than or equal to 65 y), received daily phyll oquinone (1000 mug) or placebo for 2 wk. Serum undercarboxylated osteocalci n (ucOC) and total osteocalcin, N-telopeptides of type I collagen (NTx), bo ne-specific alkaline phosphatase (BSAP), and phylloquinone concentrations w ere 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. Concomitant ly, 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 supplementa tion, serum phylloquinone concentration increased <approximate to>10-fold ( P < 0.0001) at week 1 (from 0.93 +/- 0.08 to 8.86 +/- 0.70 nmol/L, <(x)over bar> +/- SEM); this was sustained through week 2. Among all supplemented g roups, mean %ucOC decreased from 7.6% to 3.4% without significant differenc es by age or sex; 102 of 112 subjects had a > 1% decrease. Phylloquinone su pplementation reduced serum osteocalcin but did not alter NTx or BSAP conce ntration. Conclusions: Usual dietary practices in this population did not provide ade quate vitamin K for maximal osteocalcin carboxylation. Phylloquinone supple mentation reduced serum osteocalcin concentration but did not alter other m arkers of serum bone turnover.