Ruminants can recycle nitrogen (N) and phosphorus (P), which are essential for vital body processes. Reduced N- and P-intake in ruminants is desirable for economic and ecologic reasons. Simultaneous modulation of mineral homoeostasis and bone metabolism occurs in young goats. This study aimed to investigate potential effects of dietary N- and/or P-restriction on molecular changes in bone metabolism. The twenty-eight young male goats were fed a control diet, an N-reduced diet, a P-reduced diet or a combined N- and P-reduced diet for 6–8 weeks. The N-restricted goats had lower plasma Ca concentration and higher plasma osteocalcin (OC) and CrossLaps concentrations. The P-restricted goats had reduced plasma inorganic phosphate (Pi) concentrations and increased plasma Ca concentrations. Due to the initiation of a signalling pathway that inhibits the fibroblast growth factor 23 (FGF23) expression, this was lower with P-restriction. Consequently, lower Pi concentrations were the main factor influencing the reduction in FGF23. The changes in mineral homoeostasis associated with P-restriction led to a reduction in OC, bone mineral content and mineral density. Simultaneously, bone resorption potentially increased with P-restriction as indicated by an increased receptor activator of NF-κB ligand/osteoprotegerin (OPG) ratio and an increase in OPG mRNA expression. Additionally, the increased mRNA expression of the calcitonin receptor during P-restriction points to a higher number of osteoclasts. This study demonstrates an impairment of bone remodelling processes in young goats by N- or P-restriction. With P-restriction, bone mineralisation rate was potentially reduced and bone quality impaired, while with N-restriction, bone remodelling increased.

Vitamin D is a vital indicator of musculoskeletal health, as it plays an important role through the regulation of bone and mineral metabolism. This meta-analysis was performed to investigate the effects of vitamin D supplementation/fortification on bone turnover markers in women. All human randomised clinical trials reported changes in bone resorption markers (serum C-terminal telopeptide of type-I collagen (sCTX) and urinary type I collagen cross-linked N-telopeptide (uNTX)) or bone formation factors (osteocalcin (OC), bone alkaline phosphatase (BALP) and procollagen type-1 intact N-terminal propeptide (P1NP)) following vitamin D administration in women (aged ≥ 18 years) were considered. Mean differences (MD) and their respective 95 % CI were calculated based on fixed or random effects models according to the heterogeneity status. Subgroup analyses, meta-regression models, sensitivity analysis, risk of bias, publication bias and the quality of the included studies were also evaluated. We found that vitamin D supplementation had considerable effect on sCTX (MD: −0·038, n 22) and OC (MD: −0·610, n 24) with high heterogeneity and uNTX (MD: −8·188, n 6) without heterogeneity. Our results showed that age, sample size, dose, duration, baseline vitamin D level, study region and quality of studies might be sources of heterogeneity in this meta-analysis. Subgroup analysis also revealed significant reductions in P1NP level in dose less than 600 μg/d and larger study sample size (>100 participants). Moreover, no significant change was found in BALP level. Vitamin D supplementation/fortification significantly reduced bone resorption markers in women. However, results were inconsistent for bone formation markers.

The hypovitaminosis D kyphotic pig provides a model to study maternal vitamin D (D) carryover on gross and molecular characteristics of bone abnormalities in offspring. Excess maternal D is proposed to protect offspring under nutritional challenges from developing bone abnormalities. Relationships between D sufficiency parameters and bone abnormalities were characterised. Sows (n 37) were fed diets with 0 (−D), 8·125 (+D) or 43·750 (++D) µg D3/kg throughout gestation and lactation. At weaning (3 weeks) pigs were fed diets with 0 (−D) or 7·0 (+D) µg D3/kg, each with 75 and 95 % (LCaP) or 150 and 120 % (HCaP) of the Ca and P requirements. Pigs were euthanised before colostrum consumption at birth (n 27), 3 weeks (n 27) or after the nursery period (7 weeks, n 71) for tissue analysis. At 7 weeks, differences due to maternal D were detected (P≤0·05) in pig growth, serum parameters and mRNA expression regardless of nursery diet. Prevalence of kyphosis in pigs at 13 weeks was affected by maternal D, but not prevented by only HCaP or +D nursery diets. Increased (P≤0·05) serum 25-OH-D3 concentrations in sows fed +D or ++D diets were not reflected by similar magnitudes of 25-OH-D3 in colostrum, 18-d milk, or serum and tissue concentrations in pigs. The mode of action by which maternal dietary D influences development of skeletal abnormalities warrants further investigation.

The bone regeneration and healing effect of formononetin was evaluated in a cortical bone defect model that predominantly heals by intramembranous ossification. For this study, female Balb/c mice were ovariectomised (OVx) and a drill-hole injury was generated in the midfemoral bones of all animals. Treatment with formononetin commenced the day after and continued for 21 d. Parathyroid hormone (PTH1–34) was used as a reference standard. Animals were killed at days 10 and 21. Femur bones were collected at the injury site for histomorphometry studies using microcomputed tomography (μCT) and confocal microscopy. RNA and protein were harvested from the region surrounding the drill-hole injury. For immunohistochemistry, 5 µm sections of decalcified femur bone adjoining the drill-hole site were cut. μCT analysis showed that formononetin promoted bone healing at days 10 and 21 and the healing effect observed was significantly better than in Ovx mice and equal to PTH treatment in many aspects. Formononetin also significantly enhanced bone regeneration as assessed by calcein-labelling studies. In addition, formononetin enhanced the expression of osteogenic markers at the injury site in a manner similar to PTH. Formononetin treatment also led to predominant runt-related transcription factor 2 and osteocalcin localisation at the injury site. These results support the potential of formononetin to be a bone-healing agent and are suggestive of its promising role in the fracture-repair process.

Balance between adipocyte and osteoblast differentiation is the key link of disease progression in obesity and osteoporosis. We have previously reported that formononetin (FNT), an isoflavone extracted from Butea monosperma, stimulates osteoblast formation and protects against postmenopausal bone loss. The inverse relationship between osteoblasts and adipocytes prompted us to analyse the effect of FNT on adipogenesis and in vivo bone loss, triggered by high-fat diet (HFD)-induced obesity. The anti-obesity effect and mechanism of action of FNT was determined in 3T3-L1 cells and HFD-induced obese male mice. Our findings show that FNT suppresses the adipogenic differentiation of 3T3-L1 fibroblasts, through down-regulation of key adipogenic markers such as PPARγ, CCAAT/enhancer-binding protein alpha (C/EBPα) and sterol regulatory element-binding protein (SREBP) and inhibits intracellular TAG accumulation. Increased intracellular reactive oxygen species levels and AMP-activated protein kinase (AMPK) activation accompanied by stabilisation of β-catenin were attributed to the anti-adipogenic action of FNT. In vivo, 12 weeks of FNT treatment inhibited the development of obesity in mice by attenuating HFD-induced body weight gain and visceral fat accumulation. The anti-obesity effect of FNT results from increased energy expenditure. FNT also protects against HFD-induced dyslipidaemia and rescues deterioration of trabecular bone volume by increasing bone formation and decreasing bone resorbtion caused by HFD. FNT’s rescuing action against obesity-induced osteoporosis commenced at the level of progenitors, as bone marrow progenitor cells, obtained from the HFD mice group supplemented with FNT, showed increased osteogenic and decreased adipogenic potentials. Our findings suggest that FNT inhibits adipogenesis through AMPK/β-catenin signal transduction pathways and protects against HFD-induced obesity and bone loss.

Vitamin K is considered to be involved in the pathological mechanisms of coronary artery calcification (CAC). Correlation between CAC and plasma vitamin K levels was studied. A total of 103 patients, with at least one coronary risk factor, were studied. CAC was measured using 64-slice multislice computed tomography (MSCT) and divided into three groups: none (CAC score = 0; n 25), mild to moderate (0 < CAC score < 400; n 52) and severe (CAC score > 400; n 26). Phylloquinone (PK) and menaquinone (MK)-4 and MK-7 were measured by HPLC-tandem MS. Mean age of patients was 64 (sd 13) years, of which 57 % were male. Median CAC score was 57·2. Median levels of PK, MK-4 and MK-7 were 1·33, 0 and 6·99 ng/ml, showing that MK-7 was the dominant vitamin K in this population. MK-7 showed a significant inverse correlation with uncarboxylated osteocalcin (ucOC, P = 0·014), protein induced by vitamin K absence of antagonist-2 (PIVKA-2, P = 0·013), intact parathyroid hormone (P = 0·007) and bone-specific alkaline phosphatase (P = 0·018). CAC showed an inverse correlation with total circulating uncarboxylated matrix Gla protein (t-ucMGP, P = 0·018) and Hb (P = 0·05), and a positive correlation with age (P < 0·001), creatinine, collagen type 1 cross-linked N-terminal telopeptide (NTX, P = 0·03), pulse wave velocity (P < 0·001) and osteoprotegerin (P < 0·001). However, CAC did not have a significant correlation with plasma levels of PK, MK-4 or MK-7. In conclusion, plasma MK-7, MK-4 or PK level did not show significant correlation with CAC despite the association between plasma vitamin K levels and vitamin K-dependent proteins such as ucOC or PIVKA-2.

Maternal dietary vitamin D carry-over effects were assessed in young pigs to characterise skeletal abnormalities in a diet-induced model of kyphosis. Bone abnormalities were previously induced and bone mineral density (BMD) reduced in offspring from sows fed diets with inadequate vitamin D3. In a nested design, pigs from sows (n 23) fed diets with 0 (−D), 8·125 (+D) or 43·750 (++D) µg D3/kg from breeding through lactation were weaned and, within litter, fed nursery diets arranged as a 2×2 factorial design with 0 (−D) or 7·0 (+D) µg D3/kg, each with 95 % (95P) or 120 % (120P) of P requirements. Selected pigs were euthanised before colostrum consumption at birth (0 weeks, n 23), weaning (3 weeks, n 22) and after a growth period (8 weeks, n 185) for BMD, bone mechanical tests and tissue mRNA analysis. Pigs produced by +D or ++D sows had increased gain at 3 weeks (P<0·05), and at 8 weeks had increased BMD and improved femur mechanical properties. However, responses to nursery diets depended on maternal diets (P<0·05). Relative mRNA expressions of genes revealed a maternal dietary influence at birth in bone osteocalcin and at weaning in kidney 24-hydroxylase (P<0·05). Nursery treatments affected mRNA expressions at 8 weeks. Detection of a maternal and nursery diet interaction (P<0·05) provided insights into the long-term effects of maternal nutritional inputs. Characterising early stages of bone abnormalities provided inferences for humans and animals about maternal dietary influence on offspring skeletal health.

The aim of the present study was to determine whether the type of protein ingested influences the efficiency of catch-up (CU) growth and bone quality in fast-growing male rats. Young male Sprague–Dawley rats were either fed ad libitum (controls) or subjected to 36 d of 40 % food restriction followed by 24 or 40 d of re-feeding with either standard rat chow or iso-energetic, iso-protein diets containing milk proteins – casein or whey. In terms of body weight, CU growth was incomplete in all study groups. Despite their similar food consumption, casein-re-fed rats had a significantly higher body weight and longer humerus than whey-re-fed rats in the long term. The height of the epiphyseal growth plate (EGP) in both casein and whey groups was greater than that of rats re-fed normal chow. Microcomputed tomography yielded significant differences in bone microstructure between the casein and whey groups, with the casein-re-fed animals having greater cortical thickness in both the short and long term in addition to a higher trabecular bone fraction in the short term, although this difference disappeared in the long term. Mechanical testing confirmed the greater bone strength in rats re-fed casein. Bone quality during CU growth significantly depends on the type of protein ingested. The higher EGP in the casein- and whey-re-fed rats suggests a better growth potential with milk-based diets. These results suggest that whey may lead to slower bone growth with reduced weight gain and, as such, may serve to circumvent long-term complications of CU growth.

Bone metabolism fluctuates throughout the reproductive cycle of sows to enable foetal growth and milk production. Although increased bone mineralisation is conceivable in sows during reproduction, a study of mineralisation in function of parity has not been performed. This study evaluated the fluctuations of markers for bone metabolism in primiparous and multiparous sows throughout a reproductive cycle. The experiment included ten multiparous and five primiparous commercial hybrid sows from one herd. The sows were monitored for one reproductive cycle and fed according to commercial dietary standards. Blood samples were taken in the morning before feeding at fixed time intervals before (day -5) and during gestation (insemination (day 0), 21, 42, 63, 84), around parturition (day 108, 112, parturition (115), 118), and during lactation (day 122, 129, 143). Serum osteocalcin (OC) concentration increased in early and mid-gestation (P=0.002) and decreased at the end of gestation (P=0.001), whereas crosslaps (CTX) concentration decreased during early and mid-gestation (P=0.002) and increased towards the end of gestation (P=0.001). Towards the end of lactation serum levels of both markers increased (P=0.007 and 0.013, respectively). For hydroxyproline (HYP) no significant fluctuation in function of the reproductive cycle was detected. Matrix metalloproteinase 2 (MMP2) concentration increased towards parturition for both primiparous and multiparous sows (P=0.001), whereas during lactation no significant fluctuations in function of the reproductive cycle were found. A parity effect was found for OC and CTX (P<0.010), but not for the other markers. These results demonstrate that bone metabolism differed between primiparous and multiparous sows, although in both groups a similar fluctuation throughout the reproductive cycle was observed.

Population-based studies have shown an inverse association between dietary menaquinones (MK-n, vitamin K2) intake, coronary calcification and CHD risk, suggesting a potential role of vitamin K in vascular health. To date, the effects of increased menaquinone intake on (markers of) vascular health have been investigated using predominantly food supplements. Dairy products contain many essential nutrients and can serve as a good matrix for food fortification in order to support health. We were therefore interested to study the effects of a menaquinone-fortified yogurt drink (menaquinone as menaquinone-7 (MK-7); 28 µg MK-7/yogurt drink) on vitamin K status and markers of vascular health. The yogurt drink was also fortified with n-3 PUFA, vitamin D, vitamin C, Ca and Mg to support vascular and/or general health. Healthy men (n 32) and postmenopausal women (n 28) with a mean age of 56 (sd 5) years received either basic or fortified yogurt drink twice per d for 12 weeks. MK-7 was efficiently absorbed from the fortified yogurt drink. Levels of circulating MK-7 were significantly increased from 0·28 to 1·94 ng/ml. In accordance, intake of the fortified yogurt drink improved vitamin K status, as measured by significant decreases in uncarboxylated osteocalcin and desphospho-uncarboxylated matrix Gla-protein. No effects were, however, seen on markers of inflammation, endothelial dysfunction and lipid metabolism. In summary, consumption of a yogurt drink fortified with low doses of among others MK-7 for 3 months significantly improved vitamin K status in a healthy population.

Children's vitamin D intake and status can be optimised to meet recommendations. We investigated if nutritionally balanced school meals with weekly fish servings affected serum 25-hydroxyvitamin D (25(OH)D) and markers related to bone in 8- to 11-year-old Danish children. We conducted an explorative secondary outcome analysis on data from 784 children from the OPUS School Meal Study, a cluster-randomised cross-over trial where children received school meals for 3 months and habitual lunch for 3 months. At baseline, and at the end of each dietary period, 25(OH)D, parathyroid hormone (PTH), osteocalcin (OC), insulin-like growth factor-1 (IGF-1), bone mineral content (BMC), bone area (BA), bone mineral density (BMD), dietary intake and physical activity were assessed. School meals increased vitamin D intake by 0·9 (95 % CI 0·7, 1·1) μg/d. No consistent effects were found on 25(OH)D, BMC, BA, BMD, IGF-1 or OC. However, season-modified effects were observed with 25(OH)D, i.e. children completing the school meal period in January/February had higher 25(OH)D status (5·5 (95 % CI 1·8, 9·2) nmol/l; P = 0·004) than children completing the control period in these months. A similar tendency was indicated in November/December (4·1 (95 % CI –0·12, 8·3) nmol/l; P = 0·057). However, the effect was opposite in March/April (–4·0 (95 % CI –7·0, –0·9) nmol/l; P = 0·010), and no difference was found in May/June (P = 0·214). Unexpectedly, the school meals slightly increased PTH (0·18 (95 % CI 0·07, 0·29) pmol/l) compared with habitual lunch. Small increases in dietary vitamin D might hold potential to mitigate the winter nadir in Danish children's 25(OH)D status while higher increases appear necessary to affect status throughout the year. More trials on effects of vitamin D intake from natural foods are needed.

For decades, it has been debated whether high protein intake compromises bone mineralisation, but no long-term randomised trial has investigated this in children. In the family-based, randomised controlled trial DiOGenes (Diet, Obesity and Genes), we examined the effects of dietary protein and glycaemic index (GI) on biomarkers of bone turnover and height in children aged 5–18 years. In two study centres, families with overweight parents were randomly assigned to one of five ad libitum-energy, low-fat (25–30 % energy (E%)) diets for 6 months: low protein/low GI; low protein/high GI; high protein/low GI; high protein/high GI; control. They received dietary instructions and were provided all foods for free. Children, who were eligible and willing to participate, were included in the study. In the present analyses, we included children with data on plasma osteocalcin or urinary N-terminal telopeptide of collagen type I (U-NTx) from baseline and at least one later visit (month 1 or month 6) (n 191 in total, n 67 with data on osteocalcin and n 180 with data on U-NTx). The level of osteocalcin was lower (29·1 ng/ml) in the high-protein/high-GI dietary group than in the low-protein/high-GI dietary group after 6 months of intervention (95 % CI 2·2, 56·1 ng/ml, P= 0·034). The dietary intervention did not affect U-NTx (P= 0·96) or height (P= 0·80). Baseline levels of U-NTx and osteocalcin correlated with changes in height at month 6 across the dietary groups (P< 0·001 and P= 0·001, respectively). The present study does not show any effect of increased protein intake on height or bone resorption in children. However, the difference in the change in the level of osteocalcin between the high-protein/high-GI group and the low-protein/high-GI group warrants further investigation and should be confirmed in other studies.

Dermal bone is an important component of the teleost fins, and its ability to regenerate after fin amputation appears to be unlimited. The organic bone matrix contain type I collagen fibers, proteoglycans enriched in chondroitin sulfate, and noncollagenous matrix protein such as osteocalcin, osteopontin, and osteonectin. These molecules are synthesized by fin osteoblasts. Inorganic components chiefly consist of calcium and phosphate that form crystals of hydroxyapatite. Fin rays are described as models to study ossification. Due to this, the identification of the components involved in the synthesis of the organic and inorganic components of lepidotrichial bone are of great interest for the analysis of skeletal disorders in fish ossification. The present study investigates expression of alkaline phosphatase, osteopontin, osteocalcin, and chondroitin sulfate during pectoral fin regeneration in Carassius auratus gibelio. Alkaline phosphatase reaction has been found in the epidermis covering the wound, proximal blastema, near the cells that surround newly-formed lepidotrichia matrix and the tips of regenerating fin rays. Osteopontin has been observed throughout the regeneration blastema but excluded from the scleroblasts lining the inner side of the lepidotrichia. Osteocalcin and chondroitin sulfate expression coincides with the onset of mineralization of lepidotrichial matrix, suggesting its involvement in bone mineralization.

Vitamin K is required for the carboxylation of Gla-proteins in the liver (coagulation factors) and extra-hepatic tissues, such as bone (osteocalcin, OC), and arterial wall (matrix Gla-protein, MGP). Although the coagulation factors are essentially fully carboxylated under normal conditions, 10–40 % of OC and MGP remains undercarboxylated. We were therefore interested to study the dose–response effects of extra intake of menaquinones on the carboxylation of the extra-hepatic Gla-proteins. A total of forty-two healthy Dutch men and women aged between 18 and 45 years were randomised into seven groups to receive: placebo capsules or menaquinone-7 (MK-7) capsules at a daily dose of 10, 20, 45, 90, 180 or 360 μg. Circulating uncarboxylated OC (ucOC), carboxylated OC (cOC) and desphospho-uncarboxylated MGP were measured by ELISA. The ucOC:cOC ratio was calculated from circulating ucOC and cOC values. Endogenous thrombin potential and peak height were determined by calibrated automated thrombography. To increase the statistical power, we collapsed the treatment groups into three dosage groups: placebo, low-dose supplementation (doses below RDA, Commission Directive 2008/100/EC), and high-dose supplementation (doses around RDA, Commission Directive 2008/100/EC). MK-7 supplementation at doses in the order of the RDA (Commission Directive 2008/100/EC) increased the carboxylation of circulating OC and MGP. No adverse effects on thrombin generation were observed. Extra MK-7 intake at nutritional doses around the RDA (Commission Directive 2008/100/EC) improved the carboxylation of the extra-hepatic vitamin K-dependent proteins. Whether this improvement contributes to public health, i.e. increasing the protection against age-related diseases needs further investigation in specifically designed intervention trials.

Osteocalcin (OC) is a vitamin K-dependent protein found in bone and in circulation. High serum γ-carboxylated OC reflects a high, and high uncarboxylated OC (ucOC) reflects a low vitamin K status. A revolutionary hypothesis is that ucOC acts as a hormone improving glucose handling and reducing fat mass. The objective was to test the logical extrapolation of the ucOC hormone hypothesis to humans that elevated ucOC is associated with higher body weight, BMI and fat mass. In a cross-sectional analysis, the associations of vitamin K status with circulating adiponectin and body composition were investigated in 244 postmenopausal women (study I). The effects of vitamin K treatment on adiponectin, body weight and BMI were investigated in archived samples from forty-two young men and women who received varying doses of menaquinone-7 during 12 weeks (study II) and from a cohort of 164 postmenopausal women who participated in a 3-year placebo-controlled trial on 45 mg menaquinone-4 (MK-4) (study III). No association was found between vitamin K status and circulating adiponectin before or after vitamin K supplementation. A higher carboxylation of OC was significantly correlated with lower body weight, BMI and fat mass of the trunk. Women taking MK-4 maintained their baseline body weight and BMI, whereas women taking placebo showed significant increases in both indices. These findings demonstrate that a high vitamin K status of bone has no effect on circulating adiponectin in healthy people and long-term vitamin K supplementation does not increase weight in healthy postmenopausal women.

Menaquinone-7 (MK-7), a member of the vitamin K2 family, performs several functions, all related to its recognised effect on post-translational carboxylation of certain protein-bound glutamate residues. Due to its lipophilic structure MK-7 is soluble in olive oil, so the aim of the present study was to test whether extra-virgin (EV) olive oil enriched with MK-7 significantly increases MK-7 plasma levels and has an effect on osteocalcin and its carboxylation status. Healthy young volunteers (n 12) were administered 20 ml EV olive oil per d for 2 weeks, followed by 2 weeks of the same amount of olive oil enriched with 45 μg and then 90 μg MK-7, with an appropriate washout time in between. Blood was collected and plasma separated in each phase of the study. We found that integration of the diet with EV olive oil alone did not produce any significant variation of MK-7 plasma levels compared with baseline. Supplementation with MK-7-enriched olive oil resulted in a significant and dose-dependent increase in plasma levels. The high dose also significantly increased carboxylated osteocalcin (cOC) and decreased undercarboxylated osteocalcin (ucOC) plasma levels, resulting in a significant increase in the cOC:ucOC ratio. A significant correlation was also found between percentage variation of plasma cOCA:ucOC ratio and increase in plasma MK-7 levels. We conclude that regular consumption of MK-7-enriched olive oil may constitute a valid approach in order to preserve some key biochemical mechanisms controlling bone mineralisation.

Vitamin K contributes to bone health, probably through its role as cofactor in the carboxylation of osteocalcin. Intervention studies in adults have demonstrated that markedly higher osteocalcin carboxylation is obtained by intakes of vitamin K well above the current recommended dietary intake. However, the relationship between increased vitamin K2 intake and enhanced osteocalcin carboxylation has never been shown in healthy children. The objective was to study the effect of 45 μg menaquinone-7 (MK-7; one of the vitamin K2 species) on the circulating levels of undercarboxylated osteocalcin (ucOC) and carboxylated osteocalcin (cOC) in healthy prepubertal children. We hypothesised that MK-7 supplementation will reduce the ucOC:cOC ratio (UCR), indicating an improved vitamin K status. The present study is a double-blind randomised placebo-controlled trial examining the effect of 8 weeks MK-7 supplementation on the carboxylation of osteocalcin in healthy children (n 55). Serum levels of ucOC, cOC and MK-7 were measured at baseline and after 8 weeks, together with bone markers and coagulation parameters. The UCR was used as an indicator of vitamin K status. In the MK-7-supplemented group (n 28), the circulating concentration of inactive ucOC reduced and the UCR improved whereas the concentration of MK-7 increased. Within the placebo group, ucOC, cOC, UCR and MK-7 did not significantly change over time. In both groups, bone markers and coagulation parameters remained constant over time. These findings demonstrate that in healthy, prepubertal children, modest supplementation with MK-7 increases circulating concentrations of MK-7 and increases osteocalcin carboxylation.

In adult bone, vitamin K contributes to bone health, probably through its role as co-factor in the carboxylation of osteocalcin. In children, the significance of vitamin K in bone-mass acquisition is less well known. The objective of this longitudinal study was to determine whether biochemical indicators of vitamin K status are related to (gains in) bone mineral content (BMC) and markers of bone metabolism in peripubertal children. In 307 healthy children (mean age 11·2 years), BMC of the total body, lumbar spine and femoral neck was determined at baseline and 2 years later. Vitamin K status (ratio of undercarboxylated (ucOC) to carboxylated (cOC) fractions of osteocalcin; UCR) was also measured at both time points. Markers of bone metabolism, sex steroids, vitamin D status and growth hormones were measured at baseline only. Large variations in the levels of the UCR were found at both time-points, indicating a substantial interindividual difference in vitamin K status. Improvement of vitamin K status over 2 years (n 281 children) was associated with a marked increase in total body BMC (r − 49·1, P < 0·001). The UCR was associated with pubertal stage, markers of bone metabolism, sex hormones and vitamin D status. A better vitamin K status was associated with more pronounced increase in bone mass in healthy peripubertal children. In order to determine the significance of these findings for childhood bone health, additional paediatric studies are needed.

Skeletal injuries in the equine athlete are a tremendous concern with both economic and animal welfare implications. As a result, much research has focused on improving bone quality through nutritional and exercise interventions. With the recent utilization of biochemical markers, changes in bone metabolism can be monitored. This study examined and compared the response of bone markers and estimates of bone mineral content, in studies with nutritional interventions, with those utilizing exercise interventions. The post hoc analyses suggest that nutritional interventions result in less change to bone markers and bone mineral content than exercise treatments. Of the bone markers examined, osteocalcin correlates most strongly to estimates of bone quality while keratin sulphate, an indicator of cartilage turnover, showed the least correlation. Comparing the results of this study with other published studies, similar findings were observed, suggesting that small alterations in exercise play a greater role in affecting measurable changes in bone metabolism and quality of the equine athlete than do small changes in nutrition.