Dietary intake and adequacy of vitamin K

Measurement of plasma vitamin K1 (phylloquinone) and K2 (menaquinones-4 and -7) using HPLC-tandem mass spectrometry

BACKGROUND

Given the growing interest in the health benefits of vitamin K, there is great need for development of new high-throughput methods for quantitative determination of vitamin K in plasma. We describe a simple and rapid method for measurement of plasma vitamin K1 (phylloquinone [PK]) and K2 (menaquinones [MK]-4 and -7). Furthermore, we investigated the association of fasting plasma vitamin K with functional vitamin K insufficiency in renal transplant recipients (RTR).

METHODS

We used HPLC-tandem mass spectrometry with atmospheric pressure chemical ionization for measurement of plasma PK, MK-4, and MK-7. Solid-phase extraction was used for sample clean-up. Mass spectrometric detection was performed in multiple reaction monitoring mode. Functional vitamin K insufficiency was defined as plasma desphospho-uncarboxylated matrix Gla protein (dp-ucMGP) >500 pmol/L.

RESULTS

Lower limits of quantitation were 0.14 nmol/L for PK and MK-4 and 4.40 nmol/L for MK-7. Linearity up to 15 nmol/L was excellent. Mean recoveries were >92%. Fasting plasma PK concentration was associated with recent PK intake (ρ=0.41, p=0.002) and with plasma MK-4 (ρ=0.49, p<0.001). Plasma PK (ρ=0.38, p=0.003) and MK-4 (ρ=0.46, p<0.001) were strongly correlated with plasma triglyceride concentrations. Furthermore, we found that MK-4-triglyceride ratio, but not PK-triglyceride ratio, was significantly associated with functional vitamin K insufficiency (OR 0.22 [0.07-0.70], p=0.01) in RTR.

CONCLUSIONS

The developed rapid and easy-to-use LC-MS/MS method for quantitative determination of PK, MK-4, and MK-7 in human plasma may be a good alternative for the labor-intensive and time-consuming LC-MS/MS methods and enables a higher sample throughput.

Transporters for the Intestinal Absorption of Cholesterol, Vitamin E, and Vitamin K

Humans cannot synthesize fat-soluble vitamins such as vitamin E and vitamin K. For this reason, they must be obtained from the diet via intestinal absorption. As the deficiency or excess of these vitamins has been reported to cause several types of diseases and disorders in humans, the intestinal absorption of these nutrients must be properly regulated to ensure good health. However, the mechanism of their intestinal absorption remains poorly understood. Recent studies on cholesterol using genome-edited mice, genome-wide association approaches, gene mutation analyses, and the development of cholesterol absorption inhibitors have revealed that several membrane proteins play crucial roles in the intestinal absorption of cholesterol. Surprisingly, detailed analyses of these cholesterol transporters have revealed that they can also transport vitamin E and vitamin K, providing clues to uncover the molecular mechanisms underlying the intestinal absorption of these fat-soluble vitamins. In this review, we focus on the membrane proteins (Niemann-Pick C1 like 1, scavenger receptor class B type I, cluster of differentiation 36, and ATP-binding cassette transporter A1) that are (potentially) involved in the intestinal absorption of cholesterol, vitamin E, and vitamin K and discuss their physiological and pharmacological importance. We also discuss the related uncertainties that need to be explored in future studies.

Bone Health and Osteoporosis: The Role of Vitamin K and Potential Antagonism by Anticoagulants

BACKGROUND

Vitamin K's effects extend beyond blood clotting to include a role in bone metabolism and potential protection against osteoporosis. Vitamin K is required for the gamma-carboxylation of osteocalcin. Likewise, this gamma-carboxylation also occurs in the liver for several coagulation proteins. This mechanism is interrupted by coumarin-based anticoagulants in both the liver and bone.

METHODS

A thorough review of the literature on vitamin K, osteocalcin and their role in bone metabolism and osteoporosis, as well as the potential bone effects of anticoagulant therapy was conducted.

CONCLUSIONS

Epidemiological studies and clinical trials consistently indicate that vitamin K has a positive effect on bone mineral density and decreases fracture risk. Typical dietary intakes of vitamin K are below the levels associated with better BMD and reduced fracture risk; thus issues of increasing dietary intakes, supplementation, and/or fortification arise. To effectively address these issues, large-scale, intervention trials of vitamin K are needed. The effects of coumarin-based anticoagulants on bone health are more ambiguous, with retrospective studies suggesting that long-term therapy adversely affects vertebral BMD and fracture risk. Anticoagulants that do not affect vitamin K metabolism are now available and make clinical trials feasible to answer the question of whether coumarins adversely affect bone. The research suggests that at a minimum, clinicians should carefully assess anticoagulated patients for osteoporosis risk, monitor BMD, and refer them to dietitians for dietary and supplement advice on bone health. Further research is needed to make more efficacious decisions about vitamin K intake, anticoagulant therapy, and bone health.

Observations on Possible Effects of Daily Vitamin K Replacement, Especially Upon Warfarin Therapy

Daily parenteral vitamin K supplement is now recommended by the U.S. Food and Drug Administration (FDA) for patients receiving IV hyperalimentation. This is considered as preferable to the previous recommendations of weekly parenteral or oral supplement, or as in some cases no supplement at all. Supplemental vitamin K1 will ensure adequate supplies for hepatic saturation and thus the production of clotting factors II, VII, IX, and X, plus the anticoagulants protein C, protein S, and protein Z. But this is not the entire story. This recommended supplement will affect other physiologic systems that also use vitamin K-dependent gamma-carboxylation. Vitamin K is not 1 molecule but rather 2 natural substances, vitamin K1 and K2, and the synthetic K3's. It is not understood, what, if any, effect may occur because of the saturation or competition from the vitamin K1 upon the functioning of vitamins K2 and the derivatives of K3 in vivo upon bone mineralization, cell growth, and blood vessel health, all known to be influenced by the vitamins K. There are probably other physiologic systems yet to be studied relative to vitamins K and gamma-carboxylation. This review also considers the available research upon warfarin when given to patients receiving hyperalimentation and what effects the vitamin K supplements may have. Because studies to date have not controlled for vitamin K intake, consideration is given to whether one should expect any change in previously reported outcomes when using low-dose warfarin for prophylaxis against central vein thrombosis. Also considered are possible positive or negative effects that chronic warfarin therapy may have upon the other vitamin K-dependent systems under discussion. This review offers a platform for further discussion and derived clinical research provoked by this new FDA recommendation.

Phylloquinone Intakes and Food Sources and Vitamin K Status in a Nationally Representative Sample of Irish Adults

BACKGROUND

Data from a nationally representative sample of 18- to 64-y-old Irish adults conducted in 1999 highlighted low phylloquinone intakes. That survey, however, did not include older adults (aged ≥65 y), a subgroup that is potentially at higher risk of low phylloquinone intakes, or a biomarker of vitamin K status.

OBJECTIVES

The objectives of this work were to measure the phylloquinone intake and its adequacy and the serum percentage of undercarboxylated osteocalcin (%ucOC), a vitamin K status biomarker, in a nationally representative sample of Irish adults aged 18-90 y, and to compare these newer data on dietary phylloquinone in adults aged 18-64 y with those from the previous survey.

METHODS

Data and biobanked serum samples from the National Adult Nutrition Survey, a randomly selected sample of Irish adults aged 18-90 y (N = 1500), were accessed. Phylloquinone intakes were estimated from 4-d food diary data and were compared across age groups (18-35, 36-50, 51-64, and ≥65 y). Serum %ucOC was assessed by immunoassay (n = 692).

RESULTS

The mean ± SD intake of phylloquinone from all sources was 85.2 ± 59.1 μg/d, 99% of which was derived from food. Phylloquinone intakes and serum %ucOC were significantly (P < 0.05) lower (14-25%) and higher (27-39%), respectively, in the 18- to 35-y age group than in the 36- to 50-y, 51- to 64-y, and ≥65-y age groups (no differences between these 3 groups; P > 0.2 in all cases). Mean phylloquinone intakes had increased (P < 0.01) modestly (6 μg/d) in 18-64-y-olds across a decade. Of the total study population, 55% had phylloquinone intakes below the United Kingdom recommended intake of 1 μg ⋅ kg body weight^-1 ⋅ d^-1 CONCLUSION: Our study shows that younger adults (aged 18-35 y) appear to be at higher risk of inadequate vitamin K intake and lower vitamin K status, the health implications of which are unclear and warrant further investigation.

The Role of Vitamin K in Chronic Aging Diseases: Inflammation, Cardiovascular Disease, and Osteoarthritis

Vitamin K is an enzyme cofactor required for the carboxylation of vitamin K dependent proteins, several of which have been implicated in diseases of aging. Inflammation is recognized as a crucial component of many chronic aging diseases and evidence suggests vitamin K has an anti-inflammatory action that is independent of its role as an enzyme co-factor. Vitamin K-dependent proteins and inflammation have been implicated in cardiovascular disease and osteoarthritis, which are leading causes of disability and mortality in older adults. The purpose of this review is to summarize observational studies and randomized trials focused on vitamin K status and inflammation, cardiovascular disease, and osteoarthritis. Although mechanistic evidence suggests a protective role for vitamin K in these age-related conditions, the benefit of vitamin K supplementation is controversial because observational data are equivocal and the number of randomized trials is few.

Beneficial role of vitamin K supplementation on insulin sensitivity, glucose metabolism, and the reduced risk of type 2 diabetes: A review

Micronutrients are gaining acceptance as an important nutritional therapy for the prevention and/or management of diabetes and its associated health risks. Although a very small quantity of micronutrients are required for specific functions in our bodies, moderate deficiencies can lead to serious health issues. Impaired insulin sensitivity and glucose intolerance play a major role in the development of diabetic pathophysiology. Vitamin K is well known for its function in blood coagulation. Moreover, several human studies reported the beneficial role of vitamin K supplementation in improving insulin sensitivity and glucose tolerance, preventing insulin resistance, and reducing the risk of type 2 diabetes (T2 D). Both animal and human studies have suggested that vitamin K-dependent protein (osteocalcin [OC]), regulation of adipokine levels, antiinflammatory properties, and lipid-lowering effects may mediate the beneficial function of vitamin K in insulin sensitivity and glucose tolerance. This review for the first time provides an overview of the currently available preclinical and clinical evidences on the effect of vitamin K supplementation in the management of insulin sensitivity and glucose tolerance. The outcome of this review will increase understanding for the development of a novel adjuvant therapy to achieve better control of glycemia and improve the lives of diabetic patients.

NPC1L1 is a key regulator of intestinal vitamin K absorption and a modulator of warfarin therapy

Vitamin K (VK) is a micronutrient that facilitates blood coagulation. VK antagonists, such as warfarin, are used in the clinic to prevent thromboembolism. Because VK is not synthesized in the body, its intestinal absorption is crucial for maintaining whole-body VK levels. However, the molecular mechanism of this absorption is unclear. We demonstrate that Niemann-Pick C1-like 1 (NPC1L1) protein, a cholesterol transporter, plays a central role in intestinal VK uptake and modulates the anticoagulant effect of warfarin. In vitro studies using NPC1L1-overexpressing intestinal cells and in vivo studies with Npc1l1-knockout mice revealed that intestinal VK absorption is NPC1L1-dependent and inhibited by ezetimibe, an NPC1L1-selective inhibitor clinically used for dyslipidemia. In addition, in vivo pharmacological studies demonstrated that the coadministration of ezetimibe and warfarin caused a reduction in hepatic VK levels and enhanced the pharmacological effect of warfarin. Adverse events caused by the coadministration of ezetimibe and warfarin were rescued by oral VK supplementation, suggesting that the drug-drug interaction effects observed were the consequence of ezetimibe-mediated VK malabsorption. This mechanism was supported by a retrospective evaluation of clinical data showing that, in more than 85% of warfarin-treated patients, the anticoagulant activity was enhanced by cotreatment with ezetimibe. Our findings provide insight into the molecular mechanism of VK absorption. This new drug-drug interaction mechanism between ezetimibe (a cholesterol transport inhibitor) and warfarin (a VK antagonist and anticoagulant) could inform clinical care of patients on these medications, such as by altering the kinetics of essential, fat-soluble vitamins.

Vitamin K Status Is not Associated with Cognitive Decline in Middle Aged Adults

OBJECTIVES

The aim of this study was to examine the association between dephospho-uncarboxylated matrix Gla protein (dp-ucMGP), an indicator of vitamin K status, and cognitive decline, and the modifying role of 25(OH)D.

DESIGN

Longitudinal study with six years follow-up.

SETTING

Community based.

PARTICIPANTS

599 participants of the Longitudinal Aging Study Amsterdam (aged 55-65 years).

MEASUREMENTS

Information processing speed and a composite Z-score by combining three domains of cognition reflecting general cognitive functioning.

RESULTS

Generalized estimating equations (GEE) showed no significant associations between dp-ucMGP and decline in general cognitive functioning. Vitamin D modified the association between dp-ucMGP and speed of information processing (p<0.05). In the group with a 25(OH)D concentration > 50 nmol/l, the highest tertile of dp-ucMGP (>406 pmol/l), which corresponds to lower vitamin K levels, was associated with 1.5 higher score on information processing speed (p=0.023) as compared to the lowest tertile of dp-ucMGP.

CONCLUSION

In contrast to our hypothesis, a suboptimal vitamin K was not associated with cognitive decline in middle-aged adults.

Dietary intake of vitamin K in relation to bone mineral density in Korea adults: The Korea National Health and Nutrition Examination Survey (2010-2011)

Low vitamin K nutritional status has been associated with increased risk of fracture, however inconsistent results exist to support the role of vitamin K on bone mineral density depending on ethnic difference and gender. Our objective was to determine vitamin K intake in Korean adults, examine correlation between vitamin K intake and bone mineral density. This study analyzed raw data from the fifth Korea National Health and Nutrition Examination Survey for adults (2,785 men, 4,307 women) aged over 19 years. Cross-sectional analyses showed only positive association between vitamin K intake and femur bone mineral density in men after adjusting bone-related factors. However, women in high tertiles of vitamin K intake had a significantly higher bone mineral density both in femur and lumber as compared to women in lowest tertiles (p<0.05). The risk for osteoporosis was decreased as vitamin K intake increased in women, but this effect was not persisted after adjusting factors. The findings of this study indicate that low dietary vitamin K intake was associated with low bone mineral density in subjects. From these results we may suggest an increase in dietary vitamin K intakes for maintaining bone mineral density. (2010-02CON-21-C, 2011-02CON-06-C).

The health benefits of vitamin K

Vitamin K has important functions within the body, some of which are still being discovered. Research has shown that vitamin K is an anticalcification, anticancer, bone-forming and insulin-sensitising molecule. Recent data indicate that subclinical vitamin K deficiency is not uncommon. Additionally, vitamin K antagonists such as warfarin may cause detrimental side effects, which may partly be blunted through vitamin K supplementation.

Dietary Vitamin K Intake Is Associated with Cognition and Behaviour among Geriatric Patients: The CLIP Study

Our objective was to determine whether dietary vitamin K intake was associated with cognition and behavior among older adults. 192 consecutive participants ≥65 years, recruited in the cross-sectional CLIP (Cognition and LIPophilic vitamins) study, were separated into two groups according to the tertiles of dietary phylloquinone intake (i.e., lowest third below 207 µg/day versus the other two thirds combined). Daily dietary phylloquinone intake was estimated from 50-item interviewer-administered food frequency questionnaire. Cognition was assessed with Mini-Mental State Examination (MMSE); behaviour with Frontotemporal Behavioral Rating Scale (FBRS). Age, gender, social problems, education, body mass index (BMI), comorbidities, history of stroke, use vitamin K antagonists, inadequate fatty fish intake, serum thyroid-stimulating hormone (TSH), vitamin B12, albumin, and estimated glomerular filtration rate were used as confounders. Compared to participants in the lowest third of dietary phylloquinone intake (n = 64), those with higher intake had higher (i.e., better) mean MMSE score (22.0 ± 5.7 versus 19.9 ± 6.2, p = 0.024) and lower (i.e., better) FBRS score (1.5 ± 1.2 versus 1.9 ± 1.3, p = 0.042). In multivariate linear regressions, log dietary phylloquinone intake was positively associated with MMSE score (adjusted β = 1.66, p = 0.013) and inversely associated with FBRS score (adjusted β = −0.33, p = 0.037). Specifically, log dietary phylloquinone intake correlated negatively with FBRS subscore of physical neglect (r = −0.24, p = 0.001). Higher dietary phylloquinone intake was associated with better cognition and behavior among older adults.

A Dedicated Type II NADPH Dehydrogenase Performs the Penultimate Step in the Biosynthesis of Vitamin K1 in Synechocystis and Arabidopsis

Mutation of Arabidopsis thaliana NAD(P)H DEHYDROGENASE C1 (NDC1; At5g08740) results in the accumulation of demethylphylloquinone, a late biosynthetic intermediate of vitamin K1. Gene coexpression and phylogenomics analyses showed that conserved functional associations occur between vitamin K biosynthesis and NDC1 homologs throughout the prokaryotic and eukaryotic lineages. Deletion of Synechocystis ndbB, which encodes for one such homolog, resulted in the same defects as those observed in the cyanobacterial demethylnaphthoquinone methyltransferase knockout. Chemical modeling and assay of purified demethylnaphthoquinone methyltransferase demonstrated that, by virtue of the strong electrophilic nature of S-adenosyl-l-methionine, the transmethylation of the demethylated precursor of vitamin K is strictly dependent on the reduced form of its naphthoquinone ring. NDC1 was shown to catalyze such a prerequisite reduction by using NADPH and demethylphylloquinone as substrates and flavine adenine dinucleotide as a cofactor. NDC1 displayed Michaelis-Menten kinetics and was markedly inhibited by dicumarol, a competitive inhibitor of naphthoquinone oxidoreductases. These data demonstrate that the reduction of the demethylnaphthoquinone ring represents an authentic step in the biosynthetic pathway of vitamin K, that this reaction is enzymatically driven, and that a selection pressure is operating to retain type II NAD(P)H dehydrogenases in this process.

α-Tocopherol disappearance rates from plasma depend on lipid concentrations: studies using deuterium-labeled collard greens in younger and older adults

BACKGROUND

Little is known about α-tocopherol's bioavailability as a constituent of food or its dependence on a subject's age.

OBJECTIVE

To evaluate the α-tocopherol bioavailability from food, we used collard greens grown in deuterated water ((2)H collard greens) as a source of deuterium-labeled ((2)H) α-tocopherol consumed by younger and older adults in a post hoc analysis of a vitamin K study.

DESIGN

Younger (mean ± SD age: 32 ± 7 y; n = 12 women and 9 men) and older (aged 67 ± 8 y; n = 8 women and 12 men) adults consumed a test breakfast that included 120 g (2)H collard greens (1.2 ± 0.1 mg (2)H-α-tocopherol). Plasma unlabeled α-tocopherol and (2)H-α-tocopherol were measured by using liquid chromatography-mass spectrometry from fasting (>12 h) blood samples drawn before breakfast (0 h) and at 24, 48, and 72 h and from postprandial samples collected at 4, 5, 6, 7, 9, 12, and 16 h.

RESULTS

Times (12.6 ± 2.5 h) of maximum plasma (2)H-α-tocopherol concentrations (0.82% ± 0.59% total α-tocopherol), fractional disappearance rates (0.63 ± 0.26 pools/d), half-lives (30 ± 11 h), and the minimum estimated (2)H-α-tocopherol absorbed (24% ± 16%) did not vary between age groups or sexes (n = 41). Unlabeled α-tocopherol concentrations were higher in older adults (26.4 ± 8.6 μmol/L) than in younger adults (19.3 ± 4.2 μmol/L; P = 0.0019) and correlated with serum lipids (r = 0.4938, P = 0.0012). In addition, (2)H-α-tocopherol half-lives were correlated with lipids (r = 0.4361, P = 0.0044).

CONCLUSIONS

Paradoxically, α-tocopherol remained in circulation longer in participants with higher serum lipids, but the (2)H-α-tocopherol absorbed was not dependent on the plasma lipid status. Neither variable was dependent on age. These data suggest that plasma α-tocopherol concentrations are more dependent on mechanisms that control circulating lipids rather than those related to its absorption and initial incorporation into plasma. This trial was registered at clinicaltrials.gov as NCT0036232.

A four-season molecule: osteocalcin. Updates in its physiological roles

Osteocalcin (OC) is the main non-collagenous hydroxyapatite-binding protein synthesized by osteoblasts, odontoblasts, and hypertrophic chondrocytes. It has a regulatory role in mineralization and it is considered a marker of bone cell metabolism. Recent findings evidenced new extra-skeletal roles for OC, depicting it as a real hormone. OC shares many functional features with the common hormones, such as tissue-specific expression, circadian rhythm, and synthesis as a pre-pro-molecule. However, it has some peculiar features making it a unique molecule: OC exists in different forms based on the degree of carboxylation. Indeed, OC has three glutamic acid residues, in position 17, 21, and 24, which are subject to γ-carboxylation, through the action of a vitamin K-dependent γ-glutamyl carboxytransferase. The degree of carboxylation, and thus the negative charge density, determines the affinity for the calcium ions deposited in the extracellular matrix of the bone. The modulation of the carboxylation could, thus, represent the mechanism by which the body controls the circulating levels, and hence the hormonal function, of OC. There are evidences linking OC, and the bone metabolism, with a series of endocrine (glucose metabolism, energy metabolism, fertility) physiological (muscle activity) and pathological functions (ectopic calcification). Aim of this review is to give a full overview of the physiological roles of OC by collecting the newest experimental findings on this intriguing molecule.

Vitamin K: an old vitamin in a new perspective

The topic of "Vitamin K" is currently booming on the health products market. Vitamin K is known to be important for blood coagulation. Current research increasingly indicates that the antihaemorrhagic vitamin has a considerable benefit in the prevention and treatment of bone and vascular disease. Vitamin K1 (phylloquinone) is more abundant in foods but less bioactive than the vitamin K2 menaquinones (especially MK-7, menaquinone-7). Vitamin K compounds undergo oxidation-reduction cycling within the endoplasmic reticulum membrane, donating electrons to activate specific proteins via enzymatic gamma-carboxylation of glutamate groups before being enzymatically reduced. Along with coagulation factors (II, VII, IX, X, and prothrombin), protein C and protein S, osteocalcin (OC), matrix Gla protein (MGP), periostin, Gas6, and other vitamin K-dependent (VKD) proteins support calcium homeostasis, inhibit vessel wall calcification, support endothelial integrity, facilitate bone mineralization, are involved in tissue renewal and cell growth control, and have numerous other effects. The following review describes the history of vitamin K, the physiological significance of the K vitamers, updates skeletal and cardiovascular benefits and important interactions with drugs.

Canola and hydrogenated soybean oils accelerate ectopic bone formation induced by implantation of bone morphogenetic protein in mice

Canola oil (Can) and hydrogenated soybean oil (H2-Soy) are commonly used edible oils. However, in contrast to soybean oil (Soy), they shorten the survival of stroke-prone spontaneously hypertensive (SHRSP) rats. It has been proposed that the adverse effects of these oils on the kidney and testis are caused at least in part by dihydro-vitamin K (VK) 1 in H2-Soy and unidentified component(s) in Can. Increased intake of dihydro-VK1 is associated with decreased tissue VK2 levels and bone mineral density in rats and humans, respectively. The aim of the present study was to determine the effects of these oils on bone morphogenetic protein (BMP)-induced ectopic bone formation, which is promoted by VK2 deficiency, in relation to the role of VK in the γ-carboxylation of osteocalcin and matrix Gla protein. A crude extract of BMPs was implanted into a gap in the fascia of the femoral muscle in 5-week-old mice maintained on a Soy, Can, or H2-Soy diet. Newly formed bone volume, assessed by three-dimensional X-ray micro-computed tomography and three-dimensional reconstruction imaging for bone, was 4-fold greater in the Can and H2-Soy groups than in the Soy group. The plasma carboxylated osteocalcin (Gla-OC) and total OC (Gla-OC plus undercarboxylated osteocalcin [Glu-OC]) levels were significantly lower in the Can group than in the Soy group (p < 0.05). However, these levels did not significantly differ between the H2-Soy and Soy groups. The plasma Gla-OC/Glu-OC ratio in the Can and H2-Soy groups was significantly lower (in Can; p = 0.044) or was almost significantly lower (in H2-Soy; p = 0.053) than that in the Soy group. In conclusion, Can and H2-Soy accelerated BMP-induced bone formation in mice to a greater extent than Soy. Further research is required to evaluate whether the difference in accelerated ectopic bone formation is associated with altered levels of VK2 and VK-dependent protein(s) among the three dietary groups.

Assessment of potential biomarkers of subclinical vitamin K deficiency in patients with end-stage kidney disease

BACKGROUND

A significant proportion of hemodialysis patients have functional, but modifiable, vitamin K deficiency.

OBJECTIVE

To determine the correlates of poor vitamin K status in hemodialysis patients.

DESIGN

Cross-sectional study.

SETTING

Hemodialysis units at Kingston General Hospital and its satellite centres, Ontario, Canada.

PATIENTS

Patients undergoing outpatient hemodialysis for end-stage kidney disease.

MEASUREMENTS

Serum concentrations of phylloquinone, undercarboxylated prothrombin, also known as protein induced by vitamin K absence or antagonism - factor II (PIVKA-II), and the percentage of undercarboxylated osteocalcin (%ucOC).

METHODS

Vitamin K status was determined in fasting blood samples of hemodialysis patients. Bivariate relationships were examined using parametric and non-parametric statistics as appropriate. Multivariable linear regression models were applied to identify predictors of vitamin K status.

RESULTS

Among 44 HD patients, criteria for subclinical vitamin K deficiency were met in 13.6% (phylloquinone < 0.4 nmol/L), 51% (%ucOC > 20%) and 90.9% (PIVKA-II > 2.0 nmol/L) of subjects. Phylloquinone levels were positively associated with total cholesterol, triglyceride levels and non-smoking status. Higher %ucOC was associated with increased calcium-phosphate product. Increased PIVKA-II levels were observed with advancing age, reduced dialysis adequacy, lower HDL and a history of coronary artery disease. There were no associations found among the individual biomarkers of vitamin K status. In a multi-variable model, triglycerides were the only significant predictor of phylloquinone levels, while increasing phosphate and decreasing PTH were independent predictors of %ucOC. PIVKA-II levels increased by 0.54 nmol/L for every 10-year increase in age.

LIMITATIONS

Observational study; small sample size.

CONCLUSIONS

A significant proportion of HD patients met criteria for subclinical vitamin K deficiency. Of the biomarkers measured, PIVKA-II may be superior given its independence of renal function or dyslipidemia, both of which may confound the other vitamin K biomarkers. Studies in patients with ESKD linking biomarkers of vitamin K status to important patient outcomes, including cardiovascular disease, nutritional status and mortality, are required in order to determine the optimal biomarker for evaluating vitamin K status in this particular population.

Phylloquinone concentrations and the risk of vascular calcification in healthy women

OBJECTIVE

To investigate the association of plasma phylloquinone concentrations with coronary artery calcification (CAC) and vascular calcification.

APPROACH AND RESULTS

In a prospective cohort of 508 postmenopausal women, plasma phylloquinone concentrations were measured by high-pressure liquid chromatography. Calcification was measured in the coronary arteries, aortic valve, mitral valve, and thoracic aorta by multidetector computed tomography. To combine these calcification scores, we dichotomized each of the 4 areas into present or absent. Because of the continuous measurement of CAC, we categorized this as calcification present if Agatston score was >0, and calcification score was calculated as the sum of the calcified areas. Multivariate-adjusted prevalence ratios and odds ratios were estimated using Poisson regression and multinomial logistic regression. After 8.5 years of follow-up, 22% of the women had no calcification, whereas 5% had calcification in all measured areas. Detectable phylloquinone concentrations were associated with increased CAC compared with nondetectable phylloquinone concentrations with a prevalence ratio of 1.34 (95% confidence interval, 1.01-1.77). When dividing women with detectable phylloquinone concentrations into low detectable (>0-0.70 nmol/L) and moderate to high detectable (>0.70 nmol/L) phylloquinone concentrations versus nondetectable phylloquinone concentrations, both were associated with increased CAC with a prevalence ratio of 1.32 (95% confidence interval, 0.99-1.76) and 1.36 (95% confidence interval, 1.02-1.81), respectively. Detectable phylloquinone concentrations were not associated with the number of calcified areas with an odds ratio(no versus ≥ 3 areas calcifications) of 1.60 (95% confidence interval, 0.65-3.99; P=0.31).

CONCLUSIONS

Detectable phylloquinone concentrations are not associated with reduced vascular calcification but seemed to be associated with an increased prevalence of CAC.

Circulating uncarboxylated matrix Gla protein, a marker of vitamin K status, as a risk factor of cardiovascular disease

OBJECTIVES

Vitamin K plays a pivotal role in the synthesis of Matrix Gla protein (MGP), a calcification inhibitor in vascular tissue. Vascular calcification has become an important predictor of cardiovascular disease. The aim of the current study was to examine the potential association of circulating desphospho-carboxylated and -uncarboxylated MGP (dp-cMGP and dp-ucMGP), reflecting vitamin K status, with the incidence of cardiovascular events and disease (CVD) in older individuals.

STUDY DESIGN

The study was conducted in 577 community-dwelling older men and women of the Longitudinal Aging Study Amsterdam (LASA), aged >55 year, who were free of cardiovascular disease at baseline. Multivariate Cox proportional hazards models were used to analyze the data.

MAIN OUTCOME MEASURES

Incidence of CVD.

RESULTS

After a mean follow-up of 5.6±1.2 year, we identified 40 incident cases of CVD. After adjustment for classical confounders and vitamin D status, we observed a more than 2-fold significantly higher risk of CVD for the highest tertile of dp-ucMGP with a HR of 2.69 (95% CI, 1.09-6.62) as compared with the lowest tertile. Plasma dp-cMGP was not associated with the risk of CVD.

CONCLUSIONS

Vitamin K insufficiency, as assessed by high plasma dp-ucMGP concentrations is associated with an increased risk for cardiovascular disease independent of classical risk factors and vitamin D status. Larger epidemiological studies on dp-ucMGP and CVD incidence are needed followed by clinical trials to test whether vitamin K-rich diets will lead to a decreased risk for cardiovascular events.

Vitamin K and bone health in older adults

Vitamin K is one of several nutrients that have been linked with bone health. In particular, there is an emerging literature regarding the questionable efficacy of vitamin K supplementation in reducing age-related bone loss. This review aims to summarize the role of vitamin K in bone health in older adults and discuss the clinical implications from a select few human studies. The evidence for vitamin K supplementation in older adults is mixed. Although the observational studies have shown linkages between vitamin K intake and lower risk of fractures in this population, the current evidence from randomized controlled trials is not strongly supportive of vitamin K supplementation in older adults for the intent of improving bone health.

Estimation of vitamin K intake in Koreans and determination of the primary vitamin K-containing food sources based on the fifth Korean National Health and Nutrition Examination Survey (2010-2011)

There is little information on dietary vitamin K intake and nutritional status of daily requirements of vitamin K in Korea. The objective of this study was to investigate the vitamin K intake and major food sources of Vitamin K in Koreans. The survey data from the 2010-2011 Korean National Health and Nutrition Examination Survey of 7,792 subjects (aged 19-64 years) were examined. Total vitamin K intake was calculated from 24-hour dietary recall using a vitamin K food database, Computer Aided Nutritional analysis Program and the United States Department of Agriculture database. The geometric mean of vitamin K was estimated as 322.40 ± 6.33 ug/day for men and 271.20 ± 4.92 ug/day for women. Daily vitamin K intake increased significantly with age (p for trend < 0.001). The main food source of vitamin K was vegetables (72.84%), including cabbage kimchi (19.26%), spinach (17.38%), sesame leaves (7.11%), radish leaves (6.65%), spring onions (6.28%), and laver (4.82%), followed by seaweed, seasonings, and fat and oils. We observed that the vitamin K intake of Koreans was relatively higher than that reported by other studies in Western countries and differed depending on age.

Cytochrome P450-dependent catabolism of vitamin K: ω-hydroxylation catalyzed by human CYP4F2 and CYP4F11

Vitamin K plays an essential role in many biological processes including blood clotting, maintenance of bone health, and inhibition of arterial calcification. A menaquinone form of vitamin K, MK4, is increasingly recognized for its key roles in mitochondrial electron transport, as a ligand for the nuclear receptor SXR, which controls the expression of genes involved in transport and metabolism of endo- and xenobiotics, and as a pharmacotherapeutic in the treatment of osteoporosis. Although cytochrome P450 (CYP) 4F2 activity is recognized as an important determinant of phylloquinone (K1) metabolism, the enzymes involved in menaquinone catabolism have not been studied previously. CYP4F2 and CYP4F11 were expressed and purified and found to be equally efficient as in vitro catalysts of MK4 ω-hydroxylation. CYP4F2, but not CYP4F11, catalyzed sequential metabolism of MK4 to the ω-acid without apparent release of the intermediate aldehyde. The ω-alcohol could also be metabolized to the acid by microsomal NAD(+)-dependent alcohol and aldehyde dehydrogenases. LC-MS/MS analysis of trypsinized human liver microsomes (using a surrogate peptide approach) revealed the mean concentrations of CYP4F2 and CYP4F11 to be 14.3 and 8.4 pmol/mg protein, respectively. Microsomal MK4 ω-hydroxylation activities correlated with the CYP4F2 V433M genotype but not the CYP4F11 D446N genotype. Collectively, these data expand the lexicon of vitamin K ω-hydroxylases to include the 'orphan' P450 CYP4F11 and identify a common variant, CYP4F2 (rs2108622), as a major pharmacogenetic variable influencing MK4 catabolism.

Vitamin K and bone health

Vitamin K has been purported to play an important role in bone health. It is required for the gamma-carboxylation of osteocalcin (the most abundant noncollagenous protein in bone), making osteocalcin functional. There are 2 main forms (vitamin K1 and vitamin K2), and they come from different sources and have different biological activities. Epidemiologic studies suggest a diet high in vitamin K is associated with a lower risk of hip fractures in aging men and women. However, randomized controlled trials of vitamin K1 or K2 supplementation in white populations did not increase bone mineral density at major skeletal sites. Supplementation with vitamin K1 and K2 may reduce the risk of fractures, but the trials that examined fractures as an outcome have methodological limitations. Large well-designed trials are needed to compare the efficacies of vitamin K1 and K2 on fractures. We conclude that currently there is not enough evidence to recommend the routine use of vitamin K supplements for the prevention of osteoporosis and fractures in postmenopausal women.

Association between circulating vitamin K1 and coronary calcium progression in community-dwelling adults: the Multi-Ethnic Study of Atherosclerosis

BACKGROUND

Animal studies have shown that vitamin K treatment reduced vascular calcification, but human data are limited.

OBJECTIVE

We determined the association between vitamin K status and coronary artery calcium (CAC) progression in the Multi-Ethnic Study of Atherosclerosis by using a case-cohort design.

DESIGN

Serum phylloquinone (vitamin K1) was measured in 296 participants with extreme CAC progression and 561 randomly selected participants without extreme CAC progression; all subjects had baseline and follow-up CAC measures (mean follow-up: 2.5 y). A serum vitamin K1 concentration was considered low at <1.0 nmol/L (the distribution median). Outcomes were replicated by using post hoc per-protocol analyses of a vitamin K1 supplementation trial.

RESULTS

The OR (95% CI) for extreme CAC progression for subjects with low serum vitamin K1 compared with subjects without extreme CAC progression was 1.34 (0.94, 1.90; NS) when adjusted for demographics and confounders. A significant interaction between low vitamin K1 and antihypertension medication use was detected (P = 0.016). Hypertension medication users with low serum vitamin K1 were more likely to have extreme CAC progression than were medication users without extreme CAC progression [OR (95% CI): 2.37 (1.38, 4.09)]. In replication, baseline antihypertensive medication users in the supplementation group had less CAC progression than did those in the control group [adjusted mean ± SEM of the 3-y CAC change was +5 ± 20 Agatston units (AU) in the vitamin K1 group (n = 40) and +44 ± 13 AU in the placebo group (n = 49); P < 0.01].

CONCLUSIONS

Although the point estimate of our primary analysis suggests low serum vitamin K1 is associated with greater CAC progression, the difference was NS. Low serum vitamin K1 was significantly associated with CAC progression in antihypertension medication users, which, to our knowledge, is a novel finding conditionally replicated by using an independent sample. Intervention trials are needed to determine whether improving serum vitamin K1 reduces CAC progression, especially in hypertensive individuals. This trial was registered at clinicaltrials.gov as NCT00183001.

The role of menaquinones (vitamin K₂) in human health

Recent reports have attributed the potential health benefits of vitamin K beyond its function to activate hepatic coagulation factors. Moreover, several studies have suggested that menaquinones, also known as vitamin K2, may be more effective in activating extra-hepatic vitamin K-dependent proteins than phylloquinone, also known as vitamin K1. Nevertheless, present dietary reference values (DRV) for vitamin K are exclusively based on phylloquinone, and its function in coagulation. The present review describes the current knowledge on menaquinones based on the following criteria for setting DRV: optimal dietary intake; nutrient amount required to prevent deficiency, maintain optimal body stores and/or prevent chronic disease; factors influencing requirements such as absorption, metabolism, age and sex. Dietary intake of menaquinones accounts for up to 25% of total vitamin K intake and contributes to the biological functions of vitamin K. However, menaquinones are different from phylloquinone with respect to their chemical structure and pharmacokinetics, which affects bioavailability, metabolism and perhaps impact on health outcomes. There are significant gaps in the current knowledge on menaquinones based on the criteria for setting DRV. Therefore, we conclude that further investigations are needed to establish how differences among the vitamin K forms may influence tissue specificities and their role in human health. However, there is merit for considering both menaquinones and phylloquinone when developing future recommendations for vitamin K intake.

Vitamin K: novel molecular mechanisms of action and its roles in osteoporosis

Vitamin K is a fat-soluble vitamin, which is involved in blood coagulation mediated by maintaining the activity of coagulation factors in the liver. Vitamin K also has extrahepatic actions and has been shown to prevent bone fractures in clinical studies. In addition, epidemiological studies suggest that a lack of vitamin K is associated with several geriatric diseases, including osteoporosis, osteoarthritis, dementia and arteriosclerosis. It has also been shown that vitamin K contributes to the prevention and treatment of some kinds of malignancies. Recently, we discovered a novel role for vitamin K as a ligand of the nuclear receptor, steroid and xenobiotic receptor (SXR), and its murine ortholog, pregnane X receptor (PXR). In addition to its established roles as a cofactor of γ-glutamyl carboxylase (GGCX) in mediating post-transcriptional modifications, vitamin K has a different mode of action mediated by transcriptional regulation of SXR/PXR target genes. Analysis of bone tissue from PXR-deficient mice showed that the bone protective effects of vitamin K are partially mediated by SXR/PXR-dependent signaling. The discoveries of a novel mode of vitamin K action have opened up new possibilities that vitamin K might be useful for prevention or treatment of a variety of diseases that affect the geriatric population.

Vitamin K deficiency is associated with incident knee osteoarthritis

BACKGROUND

Osteoarthritis is the most common form of arthritis, with knee osteoarthritis being the leading cause of lower extremity disability among older adults in the US. There are no treatments available to prevent the structural pathology of osteoarthritis. Because of vitamin K's role in regulating skeletal mineralization, it has potential to be a preventative option for osteoarthritis. We therefore examined the relation of vitamin K to new-onset radiographic knee osteoarthritis and early osteoarthritis changes on magnetic resonance imaging (MRI).

METHODS

Subjects from the Multicenter Osteoarthritis (MOST) Study had knee radiographs and MRI scans obtained at baseline and 30 months later, and plasma phylloquinone (vitamin K) measured at baseline. We examined the relationship of subclinical vitamin K deficiency to incident radiographic knee osteoarthritis and MRI-based cartilage lesions and osteophytes, respectively, using log binomial regression with generalized estimating equations, adjusting for potential confounders.

RESULTS

Among 1180 participants (62% women, mean age 62±8 years, mean body mass index 30.1±5.1 kg/m(2)), subclinical vitamin K deficiency was associated with incident radiographic knee osteoarthritis (risk ratio [RR] 1.56; 95% confidence interval [CI], 1.08-2.25) and cartilage lesions (RR 2.39; 95% CI, 1.05-5.40) compared with no deficiency, but not with osteophytes (RR 2.35; 95% CI, 0.54-10.13). Subclinically vitamin K-deficient subjects were more likely to develop osteoarthritis in one or both knees than neither knee (RR 1.33; 95% CI, 1.01-1.75 and RR 2.12; 95% CI, 1.06-4.24, respectively).

CONCLUSION

In the first such longitudinal study, subclinical vitamin K deficiency was associated with increased risk of developing radiographic knee osteoarthritis and MRI-based cartilage lesions. Further study of vitamin K is warranted given its therapeutic/prophylactic potential for osteoarthritis.

Dietary phylloquinone intake and risk of type 2 diabetes in elderly subjects at high risk of cardiovascular disease

BACKGROUND

Limited evidence from human and animal studies has suggested that vitamin K has a potentially beneficial role in glucose metabolism and insulin resistance.

OBJECTIVE

We analyzed the cross-sectional and longitudinal associations between dietary phylloquinone intake and type 2 diabetes in elderly subjects at high cardiovascular risk.

DESIGN

Cross-sectional associations were tested in 1925 men and women in the Prevention with the Mediterranean Diet trial. A longitudinal analysis was conducted on 1069 individuals free of diabetes at baseline (median follow-up: 5.5 y). Biochemical and anthropometric variables were obtained yearly. Dietary intake was collected during each annual visit by using a food-frequency questionnaire, and phylloquinone intake was estimated by using the USDA database. The occurrence of type 2 diabetes during follow-up was assessed by using American Diabetes Association criteria.

RESULTS

Dietary phylloquinone at baseline was significantly lower in subjects who developed type 2 diabetes during the study. After adjustment for potential confounders, risk of incident diabetes was 17% lower for each additional intake of 100 μg phylloquinone/d. Moreover, subjects who increased their dietary intake of vitamin K during the follow-up had a 51% reduced risk of incident diabetes compared with subjects who decreased or did not change the amount of phylloquinone intake.

CONCLUSION

We conclude that dietary phylloquinone intake is associated with reduced risk of type 2 diabetes. This trial was registered at http://www.controlled-trials.com as ISRCTN35739639.

Nutritional interventions to prevent and treat osteoarthritis. Part II: focus on micronutrients and supportive nutraceuticals

Osteoarthritis (OA) is the most common cause of musculoskeletal disability in the elderly, and it places an enormous economic burden on society, which will remain a major health care challenge with an aging population. Management of OA is primarily focused on palliative relief using agents such as nonsteroidal anti-inflammatory drugs (NSAID) and analgesics. However, such an approach is limited by a narrow therapeutic focus that fails to address the progressive and multimodal nature of OA. Given the favorable safety profile of most nutritional interventions, identifying disease-modifying pharmaconutrients capable of improving symptoms and also preventing, slowing, or even reversing the degenerative process in OA should remain an important paradigm in translational and clinical research. The goals of pharmaconutrition for metabolic optimization are to drive biochemical reactions in a desired direction and to meet health condition-specific metabolic demands. Applying advances in nutritional science to musculoskeletal medicine remains challenging, given the fluid and dynamic nature of the field, along with a rapidly developing regulatory climate over manufacturing and commerce requirements. The purpose of this article is to review the available literature on effectiveness and potential mechanism for OA of micronutrient vitamins; minerals; glycosaminoglycans; avocado-soybean unsaponifiable fractions; methylsulfonylmethane; s-adenosylmethionine; undenatured and hydrolyzed collagen preparations; phytoflavonoid compounds found in fruits, vegetables, spices, teas, and nuts; and other nutrients on the horizon. There also is a discussion on the concept of rational polysupplementation via the strategic integration of multiple nutraceuticals with potential complementary mechanisms for improving outcomes in OA. As applied nutritional science evolves, it will be important to stay on the forefront of proteomics, metabolomics, epigenetics, and nutrigenomics, because they hold enormous potential for developing novel therapeutic and prognostic breakthroughs in many areas of medicine, including OA.

Ingestão habitual de vitamina K em adultos e idosos

OBJETIVO: O principal objetivo deste trabalho é avaliar a ingestão habitual de vitamina K em adultos e idosos. MÉTODOS: Foi realizado um estudo transversal com a participação de 173 indivíduos de ambos os sexos. A ingestão habitual de cada participante foi avaliada pela aplicação de três recordatórios 24h não consecutivos. As variabilidades intra e interpessoal foram avaliadas por meio do software PC-SIDE. RESULTADOS: A média de ingestão de vitamina K na amostra foi de 110,7µg/dia, com uma mediana de 99µg/dia; os idosos foram os que apresentaram maiores valores de ingestão, com uma mediana de 104µg/dia. O consumo de vitamina K entre adultos e idosos foi estatisticamente diferente (p=0,00), e o consumo de hortaliças apresentou forte correlação com o consumo de vitamina K total. CONCLUSÃO: Independentemente da faixa etária e do sexo, a ingestão de vitamina K foi insuficiente em quase metade da amostra, o que pode ocasionar um maior risco de inadequação dietética e acarretar problemas ósseos no futuro e/ou agravar os já presentes quando se trata da população idosa.

Phylloquinone (vitamin K(1) ) biosynthesis in plants: two peroxisomal thioesterases of Lactobacillales origin hydrolyze 1,4-dihydroxy-2-naphthoyl-CoA

It is not known how plants cleave the thioester bond of 1,4-dihydroxy-2-naphthoyl-CoA (DHNA-CoA), a necessary step to form the naphthoquinone ring of phylloquinone (vitamin K(1) ). In fact, only recently has the hydrolysis of DHNA-CoA been demonstrated to be enzyme driven in vivo, and the cognate thioesterase characterized in the cyanobacterium Synechocystis. With a few exceptions in certain prokaryotic (Sorangium and Opitutus) and eukaryotic (Cyanidium, Cyanidioschyzon and Paulinella) organisms, orthologs of DHNA-CoA thioesterase are missing outside of the cyanobacterial lineage. In this study, genomic approaches and functional complementation experiments identified two Arabidopsis genes encoding functional DHNA-CoA thioesterases. The deduced plant proteins display low percentages of identity with cyanobacterial DHNA-CoA thioesterases, and do not even share the same catalytic motif. GFP-fusion experiments demonstrated that the Arabidopsis proteins are targeted to peroxisomes, and subcellular fractionations of Arabidopsis leaves confirmed that DHNA-CoA thioesterase activity occurs in this organelle. In vitro assays with various aromatic and aliphatic acyl-CoA thioester substrates showed that the recombinant Arabidopsis enzymes preferentially hydrolyze DHNA-CoA. Cognate T-DNA knock-down lines display reduced DHNA-CoA thioesterase activity and phylloquinone content, establishing in vivo evidence that the Arabidopsis enzymes are involved in phylloquinone biosynthesis. Extraordinarily, structure-based phylogenies coupled to comparative genomics demonstrate that plant DHNA-CoA thioesterases originate from a horizontal gene transfer with a bacterial species of the Lactobacillales order.

Circulating phylloquinone concentrations of adults in the United States differ according to race and ethnicity

Differences in micronutrient status are reported to contribute to racial and ethnic differences in chronic diseases. Diseases related to vitamin K are reported to differ by race and ethnicity, but it is unclear if circulating vitamin K concentrations similarly differ. We examined racial and ethnic differences in serum phylloquionone (K1) in the Multiethnic Study of Atherosclerosis (MESA) (mean ± SD age = 62 ± 10 y; 52% female; 262 white, 180 African American, 169 Hispanic, 93 Chinese American). Overall, 25% had serum K1 <0.1 nmol/L (the lower limit of detection). The prevalence of low serum K1 was 4% in Chinese Americans compared with 24% of whites, 29% of African Americans, and 33% of Hispanics. Compared with whites, Chinese Americans were significantly less likely to have serum K1 <0.1 nmol/L [OR (95% CI): 0.23 (0.09-0.23), adjusted for serum TG, K1 intake, age, sex, BMI, smoking, total cholesterol, site, season, and lipid-lowering medication use]. African Americans and Hispanics had similar odds to whites for having serum K1 <0.1 nmol/L [OR(95% CI): 1.30 (0.79-2.15) and 1.19 (0.66-2.15), respectively; fully adjusted]. In participants with detectable concentrations (n = 523), (natural log) serum K1 was higher in the Chinese Americans compared with whites, African Americans, and Hispanics (geometric mean ± SEM = 2.2 ± 0.1 nmol/L vs. 1.2 ± 0.1 nmol/L, 1.5 ± 0.1 nmol/L, and 1.1 ± 0.1 nmol/L, respectively, adjusted for serum TG, K1 intake, and additional covariates; all P < 0.001). These findings suggest circulating K1 differs by race and ethnicity in U.S. adults, especially among those of Chinese American descent, which merits consideration in the design and interpretation of future population-based and clinical studies of vitamin K and related diseases.

Effects of vitamin E on bone turnover markers among US postmenopausal women

Increased oxidative stress and inflammation resulting from aging and declining estrogen levels can lead to increased bone loss in postmenopausal women. Alpha-tocopherol and gamma-tocopherol, the two predominant isomers of vitamin E, have antioxidant and anti-inflammatory properties, but their effects on bone metabolism have not been well studied in humans. We examined the associations between dietary and total (diet and supplements) alpha-tocopherol intake, serum alpha-tocopherol and gamma-tocopherol levels and their ratio, and bone turnover markers (BTMs) among postmenopausal women aged ≥45 years. We used cross-sectional data from the National Health and Nutrition Examination Survey 1999–2002. Multiple regression models with adjustments for relevant confounders were used to examine the associations between intake and serum levels of tocopherols, and serum bone-specific alkaline phosphatase (BAP), a biomarker of bone formation, and urinary N-telopeptides/creatinine (uNTx/Cr), a biomarker of bone resorption. The study sample included 497 postmenopausal women who were not taking estrogen, steroids, or osteoporosis medications, were free from kidney and liver disease, cancer, and rheumatoid arthritis, and were fasting >9 hours prior to examination. Participants had a mean age of 65.5 ± 0.6 years and over 45% used vitamin E (alpha-tocopherol) supplements in the past month. Vitamin E supplement users had significantly lower serum gamma-tocopherol, higher serum alpha-tocopherol levels, and higher ratio of serum alpha-tocopherol to gamma-tocopherol than nonusers. High serum gamma-tocopherol levels and low ratio of serum alpha-tocopherol to gamma-tocopherol were associated with increased BAP levels (p < 0.01 for both). There were no associations between any of the vitamin E variables and uNTx/Cr. In conclusion, we hypothesize that gamma-tocopherol may uncouple bone turnover, resulting in more bone formation than resorption. Vitamin E supplements in the form of alpha-tocopherol suppress serum gamma-tocopherol levels and may have negative effects on bone formation. Further research is needed to investigate the potential anabolic effect of gamma-tocopherol from food sources on bone.

Vascular calcification: the price to pay for anticoagulation therapy with vitamin K-antagonists

Vitamin K-antagonists (VKA) are the most widely used anti-thrombotic drugs with substantial efficacy in reducing risk of arterial and venous thrombosis. Several lines of evidence indicate, however, that VKA inhibit not only post-translational activation of vitamin K-dependent coagulation factors but also synthesis of functional extra-hepatic vitamin K-dependent proteins thereby eliciting undesired side-effects. Vascular calcification is one of the recently revealed side-effects of VKA. Vascular calcification is an actively regulated process involving vascular cells and a number of vitamin K-dependent proteins. Mechanistic understanding of vascular calcification is essential to improve VKA-based treatments of both thrombotic disorders and atherosclerosis. This review addresses vitamin K-cycle and vitamin K-dependent processes of vascular calcification that are affected by VKA. We conclude that there is a growing need for better understanding of the effects of anticoagulants on vascular calcification and atherosclerosis.

Vitamin K: food composition and dietary intakes

Vitamin K is present in the diet in the forms of phylloquinone and menaquinones. Phylloquinone, which is the major dietary source, is concentrated in leafy plants and is the vitamin K form best characterized in terms of food composition and dietary intakes. In contrast, menaquinones are the product of bacterial production or conversion from dietary phylloquinone. Food composition databases are limited for menaquinones and their presence in foods varies by region. Dietary intakes of all forms of vitamin K vary widely among age groups and population subgroups. Similarly, the utilization of vitamin K from different forms and food sources appear to vary, although our understanding of vitamin K is still rudimentary in light of new developments regarding the menaquinones.

Vitamin K-dependent carboxylation of osteocalcin: friend or foe?

Osteocalcin originates from osteoblastic synthesis and is deposited into bone or released into circulation, where it correlates with histological measures of bone formation. The presence of 3 vitamin K-dependent γ carboxyglutamic acid residues is critical for osteocalcin's structure, which appears to regulate the maturation of bone mineral. In humans, the percentage of the circulating osteocalcin that is not γ-carboxylated (percent ucOC) is used as a biomarker of vitamin K status. In contrast, when ucOC is not corrected for total osteocalcin, the interpretation of this measure is confounded by osteoblastic activity, independent of vitamin K. Observational studies using percent ucOC have led to the conclusion that vitamin K insufficiency leads to age-related bone loss. However, clinical trials do not provide overall support for the suggestion that vitamin K supplementation of the general population will reduce bone loss or fracture risk. More recently, results from in vitro and in vivo studies using animal models indicate that ucOC is an active hormone with a positive role in glucose metabolism. By inference, vitamin K, which decreases ucOC, would have a detrimental effect. However, in humans this hypothesis is not supported by the limited data available, nor is it supported by what has been established regarding osteocalcin chemistry. In summary, the specific function of osteocalcin in bone and glucose metabolism has yet to be elucidated.

Vitamin K oxygenation, glutamate carboxylation, and processivity: defining the three critical facets of catalysis by the vitamin K-dependent carboxylase

The vitamin K-dependent carboxylase uses vitamin K oxygenation to drive carboxylation of multiple glutamates in vitamin K-dependent proteins, rendering them active in a variety of physiologies. Multiple carboxylations of proteins are required for their activity, and the carboxylase is processive, so that premature dissociation of proteins from the carboxylase does not occur. The carboxylase is unique, with no known homology to other enzyme families, and structural determinations have not been made, rendering an understanding of catalysis elusive. Although a model explaining the relationship of oxygenation to carboxylation had been developed, until recently almost nothing was known of the function of the carboxylase itself in catalysis. In the past decade, discovery and analysis of naturally occurring carboxylase mutants has led to identification of functionally relevant residues and domains. Further, identification of nonmammalian carboxylase orthologs has provided a basis for bioinformatic analysis to identify candidates for critical functional residues. Biochemical analysis of rationally chosen carboxylase mutants has led to breakthroughs in understanding vitamin K oxygenation, glutamate carboxylation, and maintenance of processivity by the carboxylase. Protein carboxylation has also been assessed in vivo, and the intracellular environment strongly affects carboxylase function. The carboxylase is an integral membrane protein, and topological analysis, coupled with biochemical determinations, suggests that interaction of the carboxylase with the membrane is an important facet of function. Carboxylase homologs, likely acquired by horizontal transfer, have been discovered in some bacteria, and functional analysis of these homologs has the potential to lead to the discovery of new roles of vitamin K in biology.

Vitamin K nutrition, metabolism, and requirements: current concepts and future research

In 2001, the US Food and Nutrition Board concluded that there were insufficient data with which to establish a RDA for vitamin K, in large part because of a lack of robust endpoints that reflected adequacy of intake. Knowledge of the relative bioavailability of multiple vitamin K forms was also poor. Since then, stable isotope methodologies have been applied to the assessment of the bioavailability of the major dietary form of vitamin K in its free state and when incorporated into a plant matrix. There is a need for stable isotope studies with enhanced sensitivity to expand knowledge of the bioavailability, absorption, disposition, and metabolism of different molecular forms of vitamin K. Another area for future research stems from evidence that common polymorphisms or haplotypes in certain key genes implicated in vitamin K metabolism might affect nutritional requirements. Thus far, much of this evidence is indirect via effects on warfarin dose requirements. In terms of clinical endpoints, vitamin K deficiency in early infancy continues to be a leading cause of intracranial bleeding even in developed countries and the reasons for its higher prevalence in certain Asian countries has not been solved. There is universal consensus for the need for vitamin K prophylaxis in newborns, but the effectiveness of any vitamin K prophylactic regimen needs to be based on sound nutritional principles. In contrast, there is still a lack of suitable biomarkers or clinical endpoints that can be used to determine vitamin K requirements among adults.

Vitamin K status and vascular calcification: evidence from observational and clinical studies

Vascular calcification occurs when calcium accumulates in the intima (associated with atherosclerosis) and/or media layers of the vessel wall. Coronary artery calcification (CAC) reflects the calcium burden within the intima and media of the coronary arteries. In population-based studies, CAC independently predicts cardiovascular disease (CVD) and mortality. A preventive role for vitamin K in vascular calcification has been proposed based on its role in activating matrix Gla protein (MGP), a calcification inhibitor that is expressed in vascular tissue. Although animal and in vitro data support this role of vitamin K, overall data from human studies are inconsistent. The majority of population-based studies have relied on vitamin K intake to measure status. Phylloquinone is the primary dietary form of vitamin K and available supplementation trials, albeit limited, suggest phylloquinone supplementation is relevant to CAC. Yet observational studies have found higher dietary menaquinone, but not phylloquinone, to be associated with less calcification. Vascular calcification is highly prevalent in certain patient populations, especially in those with chronic kidney disease (CKD), and it is plausible vitamin K may contribute to reducing vascular calcification in patients at higher risk. Subclinical vitamin K deficiency has been reported in CKD patients, but studies linking vitamin K status to calcification outcomes in CKD are needed to clarify whether or not improving vitamin K status is associated with improved vascular health in CKD. This review summarizes the available evidence of vitamin K and vascular calcification in population-based studies and clinic-based studies, with a specific focus on CKD patients.

Vitamin K, an emerging nutrient in brain function

Historically discovered for its role in blood coagulation, there is now convincing evidence that vitamin K has important actions in the nervous system. As a unique cofactor to the γ-glutamyl carboxylase enzyme, vitamin K contributes to the biological activation of proteins Gas6 and protein S, ligands for the receptor tyrosine kinases of the TAM family (Tyro3, Axl, and Mer). Functionally, Gas6 has been involved in a wide range of cellular processes that include cell growth, survival, and apoptosis. In brain, vitamin K also participates in the synthesis of sphingolipids, an important class of lipids present in high concentrations in brain cell membranes. In addition to their structural role, sphingolipids are now known to partake in important cellular events such as proliferation, differentiation, senescence and cell-cell interactions. In recent years, studies have linked alterations in sphingolipid metabolism to age-related cognitive decline and neurodegenerative diseases such as Alzheimer's disease (AD). Emerging data also point to unique actions of the K vitamer menaquinone-4 (MK-4) against oxidative stress and inflammation. Finally, there is now data to suggest that vitamin K has the potential to influence psychomotor behavior and cognition. This review presents an overview of what is known of the role of vitamin K in brain function.

Vitamin K supplementation does not prevent bone loss in ovariectomized Norway rats

Background

Despite plausible biological mechanisms, the differential abilities of phylloquinone (PK) and menaquinones (MKn) to prevent bone loss remain controversial. The objective of the current study was to compare the effects of PK, menaquinone-4 (MK-4) and menaquinone-7 (MK-7) on the rate of bone loss in ovariectomized (OVX) Norway rats. A secondary aim was to compare the effects of vitamin K with those of bisphosphonates (BP) on bone loss.

Methods

Rats (n = 96) were randomized to 6 dosing groups [n = 16/group; Sham; OVX; OVX + BP (100 μg/kg/100 μg/mL saline sc); OVX + PK; OVX + MK-4; and OVX + MK-7] for 6 wk. Equimolar daily doses of 107 mg PK/kg, 147 mg MK-4/kg, and 201 mg MK-7/kg diet were provided.

Results

BP significantly increased bone strength and bone mineral density (BMD) vs. OVX (P < 0.05). However, PK, MK-4 or MK-7 did not change bone strength or BMD compared to the OVX group. Whereas supplementation of PK, MK-4 and MK-7 increased serum and tibia concentrations of each respective form, PK concentrations were consistently higher despite equimolar intakes.

Conclusion

PK, MK-4, and MK-7 do not appear to prevent bone loss in OVX rats when administered concurrent with adequate intake of other nutrients.

Functional properties, nutritional value, and industrial applications of Niger Oilseeds (Guizotia abyssinica Cass.)

Non-conventional seeds are being considered as novel food because their constituents have unique chemical properties and may augment the supply of nutritional and functional products. Niger (Guizotia abyssinica Cass.) seed and its crude oil have been widely used in traditional nutritional and medicinal applications. Consequently, niger seed has been extensively studied for its nutritional value, biological activities, and antioxidative properties. In consideration of their potential utilization, detailed knowledge on the composition of niger oilseeds is of major importance. The diversity of applications to which niger seed can be put gives this oilseed great industrial importance. This review summarizes the nutritional value, functional properties, and industrical applications of niger seeds.

The role of dietary vitamin K in the management of oral vitamin K antagonists

Vitamin K antagonists (VKA) have been the mainstay of oral anticoagulant therapy for over 60years. In this review we critically assess the evidence for the importance of vitamin K nutrition during VKA therapy; the methodologies for measuring dietary intakes; the vitamin K intake data in patients on VKA and healthy people; and the experimental evidence for the influence of vitamin K intakes and biochemical measures of vitamin K status on VKA response. Several studies show that dietary intakes of phylloquinone (vitamin K1) are associated to the sensitivity and stability of anticoagulation during initiation and maintenance dosing with low habitual intakes associated with greater instability of the INR and risk of sub-therapeutic anticoagulation. Preliminary evidence suggests that the stability of anticoagulation therapy may be improved by daily vitamin K supplementation, but further studies are needed to find out whether this, or other dietary interventions, can improve anticoagulant control in routine clinical practice.

Safety and toxicological evaluation of a synthetic vitamin K2, menaquinone-7

Menaquinone-7 (MK-7) is part of a family of vitamin K that are essential co-factors for the enzyme γ-glutamyl carboxylase, which is involved in the activation of γ-carboxy glutamate (Gla) proteins in the body. Gla proteins are important for normal blood coagulation and normality of bones and arteries. The objective of this study was to examine the potential toxicity of synthetic MK-7 in BomTac:NMRI mice and in Sprague-Dawley rats. In an acute oral toxicity test, mice were administered a single oral dose of 2000 mg/kg body weight (limit dose) and no toxicity was observed during the 14-day observation period. In the subchronic oral toxicity test in rats, animals were administered MK-7 for 90 days by gavage at the following doses: 0 (vehicle control, corn oil), 2.5, 5, and 10 mg/kg body weight/day. All generated data, including clinical observations, ophthalmology, clinical pathology, gross necropsy, and histopathology, revealed no compound-related toxicity in rats. Any statistically significant findings in clinical pathology parameters and/or organ weights noted were considered to be within normal biological variability. Therefore, under the conditions of this experiment, the median lethal dose (LD₅₀) of MK-7 after a single oral administration in mice was determined to be greater than the limit dose level of 2000 mg/kg body weight. The no observed adverse effect level (NOAEL) of MK-7, when administered orally to rats for 90 days, was considered to be equal to 10 mg/kg body weight/day, the highest dose tested, based on lack of toxicity during the 90-day study period.

Vitamin K, bone fractures, and vascular calcifications in chronic kidney disease: an important but poorly studied relationship

Vitamin K denotes a group of lipophilic vitamins determining post-translational modification of proteins. There are 2 main forms of vitamin K: vitamin K1 (phylloquinone, found in vegetables); vitamin K2 (menaquinone, produced by bacteria in the intestine and in fermented foods). Vitamin K stores are limited in humans, but it can be recycled. Vitamin K1 is principally transported to the liver, regulating the production of coagulation factors. Vitamin K2, instead, is also transported to extra-hepatic tissues, such as bone and arteries, regulating the activity of matrix Gla-protein (MGP) and osteocalcin [bone Gla-protein (BGP)]. In patients with chronic kidney disease (CKD), cardiovascular mortality is the first cause of death. Some pathogenetic mechanisms of vascular calcification (such as hyperparathyroidism, hyperphosphatemia, hypercalcemia, role of vitamin D) have been widely investigated, but the potential role of vitamin K is still uncertain. Vitamin K could play a key role, as it transforms glutamic acid residues into γ-carboxyglutamic acid, through a carboxylation process, makings both MGP (cMGP) and BGP (cBGP) biologically active. cMGP inhibits vascular calcifications (VC), while cBGP has an important role for a proper mineralization process. Uncarboxylated MGP and BGP (ucMGP and ucBGP) concentrations are indirect markers of vitamin K2 deficiency. The purpose of this review is to analyze the current literature to understand the relationship between vitamin K2 status, fragility fractures and VC in CKD patients. This analysis could be of help in planning investigations of Vitamin K status and its possible supplementation in CKD patients to avert fragility fractures and VC.