Vitamin K deficiency: an emerging player in the pathogenesis of vascular calcification and an iatrogenic consequence of therapies in advanced renal disease.

Vascular calcification is a known complication of chronic kidney disease (CKD). The prevalence of vascular calcification in patients with non-dialysis-dependent CKD stages 3-5 has been shown to be as high as 79% (20). Vascular calcification has been associated with increased risk for mortality, hospital admissions, and cardiovascular disease (6, 20, 50, 55). Alterations in mineral and bone metabolism play a pivotal role in the pathogenesis of vascular calcification in CKD. As CKD progresses, levels of fibroblast growth factor-23, parathyroid hormone, and serum phosphorus increase and levels of 1,25-(OH)2 vitamin D decrease. These imbalances have been linked to the development of vascular calcification. More recently, additional factors have been found to play a role in vascular calcification. Matrix G1a protein (MGP) in its carboxylated form (cMGP) is a potent inhibitor of vascular calcification. Importantly, carboxylation of MGP is dependent on the cofactor vitamin K. In patients with CKD, vitamin K deficiency is prevalent and is exacerbated by warfarin, which is frequently used for anticoagulation. Insufficient bioavailability of vitamin K reduces the amount of cMGP available, and, therefore, it may lead to increased risk of vascular calcification. In vitro studies have shown that in the setting of a high-phosphate environment and vitamin K antagonism, human aortic valve interstitial cells become calcified. In this article, we discuss the pathophysiological consequence of vitamin K deficiency in the setting of altered mineral and bone metabolism, its prevalence, and clinical implications in patients with CKD.

α-Tocopherol Intake Decreases Phylloquinone Concentration in Bone but Does Not Affect Bone Metabolism in Rats.

Previous studies have shown that α-tocopherol intake lowers phylloquinone (PK) concentration in some extrahepatic tissues in rats. The study's aim was to clarify the effect of α-tocopherol intake on vitamin K concentration in bone, as well as the physiological action of vitamin K. Male Wistar rats were divided into 4 groups. Over a 3-mo period, the K-free group was fed a vitamin K-free diet with 50 mg RRR-α-tocopherol/kg, the E-free group was fed a diet containing 0.75 mg PK/kg without vitamin E, the control group was fed a diet containing 0.75 mg PK/kg with 50 mg RRR-α-tocopherol/kg, and the E-excess group was fed a diet containing 0.75 mg PK/kg with 500 mg RRR-α-tocopherol/kg. PK concentration in the liver was higher in E-excess rats than in E-free rats, was lower in the tibias of control rats than in those of E-free rats, and was lower in E-excess rats than in control rats. Menaquinone-4 (MK-4) concentration in the liver was higher in E-excess rats than in E-free and control rats. However, MK-4 concentrations in the tibias of E-free, control, and E-excess rats were almost the same. Blood coagulation activity was lower in K-free rats than in the other rats but was not affected by the level of α-tocopherol intake. Additionally, dietary intake of PK and α-tocopherol did not affect uncarboxylated-osteocalcin concentration in the serum, femur density, or expression of the genes related to bone resorption and formation in the femur. These results suggest that α-tocopherol intake decreases PK concentration in bone but does not affect bone metabolism in rats.

Vitamin K: from coagulation to calcification.

Vitamin K is not only essential for the synthesis of coagulation factors in the liver, but it also strengthens the bones and prevents calcification of the arteries. These effects are mediated through the same mechanism, i.e. carboxylation of Gla target proteins. The discovery of novel Gla proteins that are not associated with blood coagulation or calcium metabolism indicates that vitamin K has additional effects in the pancreas and the central nervous system, for example. As dietary supplements, vitamin K1 of plant origin and vitamins K2 of bacterial origin may exert different effects.

Vitamin K and musculoskeletal health in postmenopausal women.

Aside from its important role in blood clotting, vitamin K is an important dietary factor in regulating bone and cartilage mineralization. The vitamin K requirements to maintain musculoskeletal health may be more than the current recommendations and subclinical vitamin K deficiency may be involved in the pathogenesis of osteoporosis and osteoarthritis. Observational studies suggest that diets low in vitamin K are associated with increased risk of fractures and osteoarthritis in older adults. However, so far randomized controlled trials of vitamin K supplementation in Caucasian populations have not shown clinically significant improvements in bone mineral density at major skeletal sites. Supplementation with vitamin K may reduce the risk of fractures, but this conclusion comes from clinical trials with methodological limitations. At this time, only one randomized controlled trial has examined the effect of vitamin K supplementation on radiographic hand osteoarthritis and found no overall effect. Large well-designed randomized controlled trials are needed to compare the efficacies of vitamin K1 and K2 on fractures and osteoarthritis among older adults. In summary, currently there is not enough evidence to recommend the use of vitamin K supplements for the prevention of bone loss, fractures, or osteoarthritis in postmenopausal women.

Cardiovascular effects of cholecalciferol treatment in dialysis patients--a randomized controlled trial.

BACKGROUND: Patients on chronic dialysis are at increased risk of vitamin D deficiency. In observational studies plasma 25-hydroxyvitamin D (p-25(OH) D) levels are inversely correlated with plasma BNP and adverse cardiovascular outcomes. Whether a causal relation exists has yet to be established. The aim of this study was to test the hypothesis that cholecalciferol supplementation improves cardiac function and reduces blood pressure (BP) and pulse wave velocity (PWV) in patients on chronic dialysis. METHODS: In a randomized, placebo-controlled, double-blind study, we investigated the effect of 75 µg (3000 IU) cholecalciferol daily for 6 months, in patients on chronic dialysis. We performed two-dimensional echocardiography, with doppler and tissue-doppler imaging, 24-h ambulatory BP (24-h BP), PWV, augmentation index (AIx), central BP (cBP) and brain natriuretic peptide (BNP) measurements at baseline and after 6 months. RESULTS: Sixty-four patients were allocated to the study. Fifty dialysis patients with a mean age of 68 years (range: 46-88) and baseline p-25(OH) D of 28 (20;53) nmol/l completed the trial. Cholecalciferol increased left ventricular (LV) volume, but had no impact on other parameters regarding LV structure or left atrial structure. LV systolic function, LV diastolic function, PWV, cBP, AIx and BNP were not changed in placebo or cholecalciferol group at follow-up. 24-h BP decreased significantly in placebo group and tended to decrease in cholecalciferol group without any difference between treatments. CONCLUSION: Six months of cholecalciferol treatment in patients on chronic dialysis did not improve 24-h BP, arterial stiffness or cardiac function. TRIAL REGISTRATION: NCT01312714, Registration Date: March 9, 2011.

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.

Osteoporosis in chronic liver disease.

Osteoporosis is a common skeletal complication seen in patients with chronic liver disease. Osteoporosis is usually asymptomatic and, if untreated, can result in fractures and impaired quality of life. For this review, we performed a systematic search of the PubMed database, and all recent peer-reviewed articles regarding the prevalence, pathophysiology, diagnosis, and management of osteoporosis in chronic liver disease were included. The prevalence of osteoporosis varies between 11% and 58% in patients with chronic liver disease and in transplant recipients. The etiology of osteoporosis is multifactorial and only partially understood. Various factors linked to the pathogenesis of bone loss are vitamin D, calcium, insulin growth factor-1, receptor activation of nuclear factor-κB ligand (RANKL), bilirubin, fibronectin, leptin, proinflammatory cytokines, and genetic polymorphisms. Management of osteoporosis involves early diagnosis, identifying and minimizing risk factors, general supportive care, nutrition therapy, and pharmacotherapy. Osteoporosis is diagnosed based on the bone mineral density (BMD) assessment using dual-energy X-ray absorptiometry scan. Measurement of BMD should be considered in all patients with advanced liver disease and in transplant recipients. Vitamin D and calcium supplementation is recommended for all patients with osteoporosis. Specific agents used for treatment of osteoporosis include bisphosphonates, calcitonin, hormonal therapy, and raloxifene. Bisphosphonates have become the mainstay of therapy for osteoporosis prevention and treatment. Prolonged suppression of bone remodeling resulting in atypical fractures has emerged as a significant complication with long-term use of bisphosphonates. Newer treatment agents and better fracture prevention strategies are necessary to prevent and treat osteoporosis.

Bleeding tendency in an adolescent with chronic small bowel obstruction.

We report a case of fat-soluble vitamin deficiency in a 14-year old boy who had chronic duodenal obstruction. He presented with periodic unexplained bleeding tendency. The laboratory results showed positive fat globules in stool and prolonged prothrombin time. His further investigation revealed low plasma vitamin A and undetectable plasma vitamin E. After parenteral vitamin K and oral vitamin A and E supplement, these abnormalities resolved although he still had absent knee jerk. We propose that fat malabsorption and fat-soluble vitamin deficiency can occur after prolonged duodenal obstruction that induce bacterial overgrowth following by bile acid deconjugation. Despite very few case reports, screening for fat malabsorption and fat-soluble vitamin deficiency might be warranted in patients with chronic small bowel obstruction.

Association of vitamin K status with adiponectin and body composition in healthy subjects: uncarboxylated osteocalcin is not associated with fat mass and body weight.

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.

Risk factors of acquired prothrombin complex deficiency syndrome: a case-control study.

BACKGROUND: Idiopathic vitamin K deficiency in infancy or acquired prothrombin complex deficiency (APCD) is a serious bleeding disorders in infants. It leads to a high mortality rate and permanent neurological sequele among the survivors. A low vitamin K intake by infants is suggested to have a major role in the pathogenesis. To reduce the incidence of this syndrome, its risk factors have to be identified. OBJECTIVE: To determine the risk factors of the acquired prothrombin complex deficiency syndrome in the early infantile period. MATERIAL AND METHOD: A case-control study was conducted in 20 cases and 60 age- and sex-matched controls who were admitted to the Queen Sirikit National Institute of Child Health in Bangkok during August 1991 to August 1993. Feeding type, maternal history of herb-liquor extracts (herbal medicine) use and no history of vitamin K1 prophylactics at birth were identified to be risk factors of the syndrome. All subjects were fed by breast milk with or without formula milk. None of the subjects fed by formula milk were in the case group (Chi-square for trend = 14.77, p = 0.001). RESULTS: The rate of a maternal history of herb-liquor extracts use in the case group was significantly higher than that of the control group (p = 0.03). Vitamin K2MK4 level in breast milk obtained from the mothers of the infants with maternal history of herb-liquor extracts use was lower than that obtained from the mothers of the infants without maternal history of herb-liquor extracts use (p = 0.03). No infant with history of intramuscular K1 prophylactics was in the case group. Three out of eight infants with history of oral vitamin K1 regimen were cases. Although vitamin K1 and K2MK4 level in breast milk obtained from the cases' mothers were significantly lower than that obtained from the controls' mothers (p = 0.015 and p = 0.003 respectively), there was an overlapping of vitamin K levels among these two groups. CONCLUSION: This study demonstrated that vitamin K in breast milk has a main role in the pathogenesis of this disease. Herb-liquor extracts may be a cause of the APCD syndrome. Intramuscular vitamin K1 prophylactics should be routinely given to all newborn babies who will receive breast feeding. Effectiveness of oral vitamin K1 prophylactics regimen must be studied urgently.

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.

Vitamin K status may be an important determinant of childhood bone health.

There has been relatively little research emphasis on the effect of vitamin K on bone health during childhood. Recent interesting data from an observational study of healthy young girls (aged 3-16 years) in the United States suggests that better vitamin K status is associated with lower levels of markers of bone resorption and bone formation, suggesting a lower rate of bone turnover. However, in that study, vitamin K status was not consistently associated with bone mineral content or gain in bone mineral content over 4 years. There is a need for randomized phylloquinone supplementation trials to better understand the role of vitamin K on bone acquisition in growing children.

Viability and plasma vitamin K levels in the common bile duct-ligated rats.

The common bile duct-ligated (CBDL) rat, which is widely used as a model of human cirrhosis, rapidly develops secondary biliary cirrhosis (SBC) within 4 weeks. The CBDL rat shows poor viability, however, a detailed examination of the causes of its death has not been made. In this study, we investigated the outcome of bile duct ligation in detail and attempted to extend the life span of this model by feeding the animals a diet supplemented with nutrients. Survival rate, blood chemistry, blood cell counts, plasma levels of K vitamins and liver histology were compared among CBDL rats fed a standard diet and an enriched diet. Sham-operated rats were used as a control. Six out of 18 CBDL rats fed the standard diet died within 32 days of operation. The cause of death was massive internal hemorrhage in various organs or body cavities. All CBDL rats fed the enriched diet survived more than 31 days, but the viability of CBDL rats was not significant between those fed the standard diet and the enriched diet. The degree of anemia correlated significantly with the prolongation of prothrombin time. Plasma vitamin K1 levels in CBDL rats were significantly lower than those in sham-operated rats, but vitamin K2 levels were similar. We suggest that massive hemorrhage, which was the direct cause of death, is caused by the impairment of hemostasis resulting from vitamin K deficiency. The enriched diet with vitamin K nutritional supplements seemed to contribute to the prolongation of the life span of CBDL rats.

Vitamin K requirement in Danish anticoagulant-resistant Norway rats (Rattus norvegicus).

Resistance to warfarin has been connected to an increase in dietary requirement for vitamin K in British strains of the Norway rat, Rattus norvegicus (Berk). This study examines vitamin K requirement of Danish anticoagulant-resistant Norway rats using a vitamin K deficient feeding test. Wild bromadiolone-resistant rats sampled from different localities in Denmark and rats from bromadiolone-resistant and susceptible laboratory strains were fed on a vitamin K deficient diet over a maximum period of 15 days. Development of vitamin K deficiency, measured as reduced blood-clotting capacity, took place in 43% of the Danish resistant rats and was independent of sex, treatment with supplementary vitamin K3 and sampling locality. Development of deficiency was slower for resistant rats that were supplemented with vitamin K3 prior to the feeding test, suggesting storage of the vitamin K in a vitamin body pool. Intraperitoneal administration of vitamin K1 revealed that 80 microg vitamin K1 kg(-1) bodyweight was sufficient to restore normal blood clotting activity in deficient rats, while 60 microg vitamin K1 kg(-1) bodyweight was insufficient. We conclude that vitamin K requirement is moderately increased in Danish homozygous resistant rats whereas heterozygous resistant rats only have a minor increase in vitamin K requirement compared with susceptible rats. We found no indication of different resistance types being present in our test material since vitamin K requirement was not different between rats from separate sampling localities.

Dietary vitamin K intakes are associated with hip fracture but not with bone mineral density in elderly men and women.

BACKGROUND: Vitamin K has been associated with bone mineral density (BMD) and risk of hip fracture. The apolipoprotein (apo) E4 allele (APOE*E4) has been associated with bone fracture through a putative effect on vitamin K transport in blood. OBJECTIVE: The objective was to determine the associations between vitamin K intake, apo E genotype, BMD, and hip fracture in a population-based cohort of elderly men and women. DESIGN: Dietary vitamin K intake was assessed with a food-frequency questionnaire in 335 men and 553 women (average age: 75.2 y) participating in the Framingham Heart Study in 1988-1989. Incidence of hip fractures was recorded from 1988 to 1995. BMD at the hip, spine, and arm was assessed on 2 separate occasions (1988-1989 and 1992-1993). Comparisons between apo E genotype and BMD were made relative to E4 allele status (at least 1 epsilon4 allele compared with no epsilon4 allele). RESULTS: Individuals in the highest quartile of vitamin K intake (median: 254 microg/d) had a significantly lower fully adjusted relative risk (0.35; 95% CI: 0. 13, 0.94) of hip fracture than did those in the lowest quartile of intake (median: 56 microg/d). There were no associations between vitamin K intake and BMD in either men or women. No association was found between the E4 allele and BMD, and there were no significant interactions between the E4 allele and phylloquinone intake and BMD or hip fracture. CONCLUSIONS: Low vitamin K intakes were associated with an increased incidence of hip fractures in this cohort of elderly men and women. Neither low vitamin K intake nor E4 allele status was associated with low BMD.

Diet- or warfarin-induced vitamin K insufficiency elevates circulating undercarboxylated osteocalcin without altering skeletal status in growing female rats.

To further characterize the skeletal role of vitamin K (K), markers of bone turnover, density, and strength were evaluated in rats with diet- or warfarin (W)-induced K insufficiency. One hundred two, 7-week-old, female rats were randomly assigned to low K (phylloquinone [K1], 20 microg/kg diet), control K (K1, 1300 microg/kg diet), low-dose W (W, 1.5 mg/kg control diet), or high-dose W plus K (W/K1, 10/100 mg/kg diet). Femur bone mineral content (BMC) and bone mineral density (BMD), plasma prothrombin time (PT) and prothrombin concentration (PC), and serum total alkaline phosphatase (ALP) and skeletal alkaline phosphatase (sALP) were measured at baseline and days 20, 40, 60, and 80. Serum total osteocalcin (OC) and undercarboxylated osteocalcin (ucOC) and femur length (FL) were measured at baseline and day 80. Left femur OC was measured and biomechanical testing of the right femur and third lumbar vertebral body was performed at day 80. Low dietary K elevated circulating ucOC (17% higher than control; p < 0.0001) at day 80. Furthermore, in both W groups, essentially all circulating OC was undercarboxylated and femur OC was lower than control (p < 0.0001). However, there was no change in femur percent ucOC, suggesting deposition of less newly synthesized OC. No between group differences were observed in PT, ALP, sALP, FL, BMC, BMD, or bone strength. In conclusion, skeletal K insufficiency can be induced by W or diet manipulation. This does not hinder peak bone mass attainment in female rats; however, W causes less newly synthesized OC to be deposited in bone.

Prevention of vitamin K deficiency bleeding: efficacy of different multiple oral dose schedules of vitamin K.

UNLABELLED: There is consensus that late vitamin K deficiency bleeding (VKDB) should be prevented by vitamin K prophylaxis. One single dose of 1 mg vitamin K1 is effective if given i.m. or s.c., but not if given orally. Repeated oral doses might be as effective as the parenteral dose but the optimal dose regimen remains to be established. Different oral dose schedules are presently used in different countries. In Australia, Germany, The Netherlands and Switzerland active surveillance data on late VKDB were collected in a similar manner and failure rates compared. Identical case definitions were used. There were three basic strategies for oral and one for parenteral vitamin K prophylaxis for healthy newborns in the four countries: (1) daily supplementation of low dose vitamin K (25 micrograms) for breast-fed infants (The Netherlands); (2) 3 x 1 mg orally [Australia (January 1993-March 1994) and Germany (December 1992-December 1994)]; (3) 1 mg vitamin K i.m. (Australia since March 1994); and (4) 2 x 2 mg vitamin K (new mixed micellar preparation) (Switzerland). The respective failure rates per 100,000 live births (including cases given all recommended doses and those given incomplete prophylaxis) were for strategy: (1) 0.2 (0-1.3) in The Netherlands; (2) 2.3 (95% CI 1.6-3.4) in Germany and 2.5 (1.1-4.8) in Australia (oral prophylaxis); (3) Australia (i.m. prophylaxis) 0 (0-0.9); and (4) 3.6 (0.7-10.6) in Switzerland. The failure rates for complete prophylaxis only were: strategy (1) 0 (0-0.7) in The Netherlands; (2) 1.8 (1.1-2.8) in Germany and 1.5 (0.5-3.6) in Australia; (3) Australia (i.m.) 0 (0-0.9); and (4) 1.2 (0-6.5) in Switzerland. CONCLUSIONS: The Australian data confirm that three oral doses of 1 mg vitamin K are less effective than i.m. vitamin K prophylaxis. A daily low oral dose of 25 micrograms vitamin K1 following an initial oral dose of 1 mg after birth for exclusively breast-fed infants may be as effective as parenteral vitamin K prophylaxis. The effectiveness of the "mixed-micellar" preparation of vitamin K1 needs further study.

Nutritional aspects of hip fractures.

Prevalence of malnutrition, particularly undernutrition, increases with advancing age, and patients with hip fracture are often particularly malnourished and/or undernourished. Deficiency in both micronutrients and macronutrients appears to be strongly implicated in the pathogenesis and the consequences of hip fracture in osteoporotic elderly. Such deficiencies can accelerate age-dependent bone loss, increase the propensity to fall by impairing movement coordination, and affect protective mechanisms that reduce the impact of falling. With respect to micronutrients, the most documented information concerns calcium and vitamin D. Studies conducted in the elderly have shown that administration of calcium and vitamin D can reduce femoral bone loss and, in institutionalized patients, lower the incidence of hip fracture. Besides hypovitaminosis D, deficiency in vitamin K has been suggested to contribute to bone fragility in patients sustaining hip fracture. As far as macronutrients are concerned, low protein intake appears to play a distinct detrimental role in the causes and complications of hip fracture. In a recent survey in hospitalized elderly patients, reduced protein intake was associated with lower femoral neck bone mineral density (BMD) and poor physical performance. This observation is in keeping with several studies in which a state of energy-protein malnutrition was documented in elderly patients with hip fracture. In these patients, in whom we detected very low femoral neck bone mineral density at the level of the proximal femur, the self-selected intake of protein and energy was insufficient during their hospital stay. Interestingly, the clinical outcome after hip fracture was significantly improved by daily oral nutritional supplement normalizing the protein intake, documented as a reduction in both complication rate and median duration of hospital stay. Further studies showed that normalization of the protein intake, independently of that of energy, calcium, and vitamin D, was responsible for this more favorable outcome. Preliminary data suggest that protein supplementation may also reduce further bone loss in elderly patients having sustained hip fracture. Increasing the protein intake from low to normal could act through an increase in the plasma level of IGF-I, a growth factor that exerts a positive effect on bone mass and that has been found to decrease with aging.

Observations on vitamin K deficiency in the fetus and newborn: has nature made a mistake?

The microsomal mixed function oxidase system metabolizes xenobiotics (Phase I) to products that, if not activated and conjugated for excretion (Phase II), are capable of forming conjugates with cellular macromolecules, including DNA, resulting in toxic, mutagenic, or carcinogenic events. Benzo(a)pyrene (BP), a polycyclic aromatic hydrocarbon, is a model carcinogen for this system. Vitamin K1 (phylloquinone) is a regulator of BP metabolism. These studies demonstrate that K1 is capable of increasing Phase I metabolism and decreasing glutathione transferase activity (Phase II) in chick embryo liver; that deprivation of K1 reduces BP/DNA adducts in mouse liver and reduces tumor formation in mice given intraperitoneal BP; and that K1 supplementation increases BP induced tumor formation in mice. However, epidemiologic studies indicate that children of mothers who smoke during pregnancy may not be at increased risk of cancer. It is known that the placentas from these pregnancies exhibit markedly increased levels of arylhydrocarbon hydroxylase induced by the polycyclic aromatic hydrocarbons in tobacco smoke, but there is no corresponding increase in this enzyme activity in the fetus in such pregnancies. We suggest that the low vitamin K level is a secondary protective mechanism for xenobiotics, such as BP, that may escape the primary placental screen. The recently described role of vitamin K-dependent Gla protein as ligands for receptor tyrosine kinases, also establishes K as a link in cell growth and transformation. It is proposed that the small total body pool of K1 in the adult, which is sufficient only to meet continuing needs, and the even smaller pool in the fetus are protective. This protective effect of low K1 levels is particularly important in the presence of the high mitotic rates and rapid cell turnover in the avian embryo and mammalian fetus.