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Circulating species of matrix Gla protein and the risk of vascular calcification in healthy women
International Journal of Cardiology 168 (2013) e168–e170
Contents lists available at ScienceDirect
International Journal of Cardiology journal homepage: www.elsevier.com/locate/ijcard
Letter to the Editor
Circulating species of matrix Gla protein and the risk of vascular calcification in healthy women Geertje W. Dalmeijer a,⁎,1, Yvonne T. van der Schouw a,1, Elke J. Magdeleyns b,1, Cees Vermeer b,1, Sjoerd G. Elias a, Birgitta K. Velthuis c,1, Pim A. de Jong c,1, Joline W.J. Beulens a,1 a b c
Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, The Netherlands VitaK, Maastricht University, The Netherlands Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
a r t i c l e
i n f o
Article history: Received 25 July 2013 Accepted 19 August 2013 Available online 27 August 2013 Keywords: Matrix Gla protein Vascular calcification. CAC MGP CVD
Observational studies showed that high vitamin K intake is associated with reduced coronary artery calcification (CAC) and cardiovascular disease (CVD) risk [1,2]. These effects are thought to be mediated by increased activation of the vitamin K-dependent protein matrix-Gla protein (MGP) [3]. However, only few studies investigated the relation of different MGP species with CAC and none of these studies were performed in the general population [4]. The aim of this prospective study is to investigate the association between circulating MGP species and vascular calcification among healthy women. This study was performed in a prospective cohort of 571 women aged 57.3 (±5.2) years, described in detail elsewhere [5,6]. Baseline plasma MGP levels were measured by ELISA techniques [7]. Calcification was measured in the coronary arteries, aortic valve, mitral valve, and aortic arch by multi-detector computed tomography after 8.5 (±1.3) years of follow-up and graded as present or absent. CAC was present if Agatston score was ≥10. The calcification score was calculated as the sum of the calcified areas. Modified Poisson regression was used to estimate relative risks (RR) for the association between MGP and CAC. Multinomial logistic regression was used to estimate odds ratios (OR) for the association between MGP or vitamin K with calcified areas, since this is an ordinal outcome. ⁎ Corresponding author at: Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, STR 6.131, PO Box 85500, 3508 GA Utrecht, The Netherlands. Tel.: +31 88 7568050; fax: +31 88 7568099. E-mail address: [email protected] (G.W. Dalmeijer). 1 This author takes responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation. 0167-5273/$ – see front matter © 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijcard.2013.08.062
In this population, 43% had CAC, 22% aortic valve calcification, 11% mitral valve calcification and 62% aortic calcification. High desphosphouncarboxylated MGP (dp-ucMGP) concentrations, reflecting poor vitamin K status, were borderline significantly (p = 0.08) associated with more CAC (RRSD: 1.07; 95%CI: 0.99–1.15) and calcified areas with an ORSD of 1.49 (95%CI: 0.95–2.35, p = 0.09) for 4 calcified areas versus no calcified areas adjusted for age, follow-up time, smoking, BMI, blood pressure and HDL-cholesterol (Table 1). High total-uncarboxylated MGP (t-ucMGP) concentrations were borderline significantly associated with fewer calcified areas (ORSD(4 vs 0 areas) 0.63; 95%CI: 0.36–1.10, p = 0.10). However, circulating t-ucMGP was not associated with the presence of CAC (RRSD: 1.06; 95%CI: 0.98–1.16, p = 0.17). This was due to the presence of a nonlinear relation as indicated by a significant quadratic term (p = 0.03). Spline regression showed evidence of a U-shaped relation (p = 0.13) between t-ucMGP and coronary calcification with lower presence of CAC up to 3.2 nM, but increasing RRs at higher levels (Fig. 1). Circulating desphosho-carboxylated MGP (dp-cMGP) was not associated with calcification. After adjustment, high phylloquinone intake was not associated with the number of calcified areas ORSD(4 vs 0 areas) 1.14 (95%CI: 0.72–1.81, p = 0.57). However, high menaquinone intake was significantly associated with decreased odds of having four calcified areas. Per SD increase in menaquinone, the odds of having four calcified areas was 61% lower (OR 0.39; 95%CI: 0.21–0.74, p = 0.004; Table 1). Both high phylloquinone (βSD:−0.043; 95%CI: −0.070; −0.016) and menaquinone (βSD: −0.032; 95%CI: −0.059; −0.009) intake were associated with lower dp-ucMGP concentrations adjusted for age, BMI and smoking. This prospective study shows that high dp-ucMGP concentrations may be associated with higher risk of CAC and more calcified areas. High t-ucMGP concentrations seem to be associated with fewer calcified areas. Furthermore, high menaquinone intake was associated with fewer calcified areas and lower dp-ucMGP concentrations. A previous study in this study population showed that high menaquinone intake, but not phylloquinone, was associated with reduced CAC [1]. We now show that high menaquinone intake is also associated with fewer calcified areas. Phylloquinone intake, however, was not associated with calcification. These results are in line with previous observational studies on vitamin K intake in relation to CAC and coronary heart disease [1,2,8]
G.W. Dalmeijer et al. / International Journal of Cardiology 168 (2013) e168–e170
e169
Table 1 Relative risks (95%-CI) of circulating levels of MGP species with coronary calcification and odds ratios (95%-CI) of MGP species, menaquinone and phylloquinone with calcification among 571 post-menopausal womena. CAC
calcified areas 0
N = 249
dp-ucMGP Model 1c Model 2d t-ucMGP Model 1c Model 2d dp-cMGP Model 1c Model 2d phylloquinone Model 1c Model 2d menaquinone Model 1c Model 2d
N = 138
RRb
95%CI
1.06 1.07
0.99–1.13 0.99–1.15
1.08 1.06 1.01 1.01
1
2
N = 179
3
N = 165
4
N = 55
N = 22
ORb
95%CI
ORb
95%CI
ORb
95%CI
ORb
95%CI
1 1
1.33 1.28
1.00–1.76 0.95–1.72
1.33 1.25
0.99–1.79 0.91–1.71
1.50 1.47
1.06–2.13 1.02–2.12
1.49 1.49
0.98–2.26 0.95–2.35
0.99–1.18 0.98–1.16
1 1
0.89 0.84
0.70–1.13 0.65–1.09
1.20 1.08
0.94–1.55 0.83–1.41
1.14 1.02
0.81–1.59 0.72–1.46
0.75 0.63
0.44–1.27 0.36–1.10
0.93–1.10 0.92–1.11
1 1
1.27 1.22
0.99–1.64 0.94–1.59
1.43 1.33
1.09–1.86 1.00–1.76
1.13 1.05
0.78–1.63 0.71–1.56
1.09 1.07
0.65–1.83 0.61–1.86
1 1
0.83 0.83
0.66–1.04 0.66–1.06
0.95 0.94
0.75–1.21 0.73–1.21
0.84 0.83
0.60–1.19 0.59–1.18
1.17 1.14
0.75–1.82 0.72–1.81
1 1
0.86 0.88
0.69–1.08 0.69–1.11
0.90 0.93
0.71–1.14 0.72–1.20
0.93 0.94
0.67–1.29 0.67–1.32
0.35 0.39
0.20–0.64 0.21–0.74
MGP, Matrix Gla protein; dp-ucMGP, desphospho-uncarboxylated MGP; dp-cMGP, desphospho carboxylated MGP; t-ucMGP, total uncarboxylated MGP. a Modified Poisson regression model was used to estimate relative risks (RR) for the association between MGP species and presence of CAC. Multinomial logistic regression was used to estimate odds ratios (OR) for the association between MGP species or vitamin K intake with calcified areas. The group with one to four calcified areas was compared with the group without calcification in any area. b All RRs and ORs are expressed per SD of the mean. c Adjusted for age, follow up time. d Adjusted for age, follow up time, smoke habits, BMI, blood pressure and HDL-cholesterol.
We observed borderline significant associations between high dpucMGP concentrations and CAC and more calcified areas. This is in line with the results of our cross-sectional study showing a borderline
Fig. 1. Association between t-ucMGP circulating levels and relative risk of CAC modelled continuously using splines; RR(—) with 95%CI in grey.
significant association between high dp-ucMGP and high CAC [6]. Similarly, previous studies reported higher dp-ucMGP concentrations among patients with diseases characterized by vascular calcification [4]. However, in another cross-sectional study among healthy adults, no association between dp-ucMGP and CAC was found [8]. Because this form of MGP has very low affinity for deposited calcium salts, the influence of vitamin K intake is directly observed in the circulation. Previous studies have shown that dp-ucMGP could be a sensitive marker of vitamin K intake and status with low concentrations reflecting a high vitamin K status or intake [3]. In line with these studies [4] we found that low dp-ucMGP concentrations were associated with high phylloquinone and menaquinone intake. Altogether, these results suggest that low dp-ucMGP concentrations could explain the reduced risk of CAC with high vitamin K intake. Similar to high-risk populations [4], we found that low t-ucMGP levels were associated with more calcified areas. Due to the presence of a U-shaped relation between t-ucMGP and CAC we did not find an association using linear regression. However, similar to the association with number of calcified areas, spline regression also showed slightly lower RRs for CAC up to 3.2 nM t-ucMGP, which increased at higher concentrations. We assume that t-ucMGP mainly consists of phosphorylated ucMGP species. The phosphoserines equip the molecule with strong calcium-binding groups irrespective of its Gla content and this fraction has a strong affinity to bind to vascular calcifications, resulting in a decrease in the circulating levels of t-ucMGP. This explains the lower t-ucMGP concentrations at higher CAC [9]. Therefore, t-ucMGP may act differently in persons with or without calcification. A limitation of our study is that the dp-ucMGP and dp-cMGP levels were low compared to a healthy reference population [7]. This could be due to the possible degradation of MGP in our samples, because the samples were stored for a long time. However, we compared the levels with those measured previously [6] and found reasonable correlation coefficients of 0.67 for dp-ucMGP and 0.51 for t-ucMGP. We therefore assume that degradation of MGP did not substantially affect the ranking of individuals and did not systematically bias the associations we found. Taken together, high dp-ucMGP concentrations, reflecting a poor vitamin K status, may be associated with more calcification, which
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could explain the reduced CAC risk with high vitamin K intake. High t-ucMGP concentrations seem to be associated with fewer calcified areas. Acknowledgements This research was supported by a personal Dr. Dekker postdoctoral grant (2008 T062) from the Netherlands Heart Foundation (JW Beulens). The data collection of this study was financially supported by grant 2100.0078 from the Netherlands Organization of Health Research and Development. The authors declare to have no conflict of interest. Cees Vermeer is CEO of VitaK B.V., The Netherlands. There was no commercial funding involved. References [1] Beulens JW, Bots ML, Atsma F, et al. High dietary menaquinone intake is associated with reduced coronary calcification. Atherosclerosis 2009;203:489–93.
[2] Geleijnse JM, Vermeer C, Grobbee DE, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr 2004;134:3100–5. [3] Schurgers LJ, Cranenburg EC, Vermeer C. Matrix Gla-protein: the calcification inhibitor in need of vitamin K. Thromb Haemost 2008;100:593–603. [4] Theuwissen E, Smit E, Vermeer C. The role of vitamin K in soft-tissue calcification. Adv Nutr 2012;3:166–73. [5] Atsma F, Bartelink ML, Grobbee DE, et al. Reproductive factors, metabolic factors, and coronary artery calcification in older women. Menopause 2008;15:899–904. [6] Dalmeijer GW, van der Schouw YT, Vermeer C, Magdeleyns EJ, Schurgers LJ, Beulens JW. Circulating matrix Gla protein is associated with coronary artery calcification and vitamin K status in healthy women. J Nutr Biochem 2013;24:624–8. [7] Shea MK, O'Donnell CJ, Vermeer C, et al. Circulating uncarboxylated matrix gla protein is associated with vitamin K nutritional status, but not coronary artery calcium, in older adults. J Nutr 2011;141:1529–34. [8] Cranenburg EC, Brandenburg VM, Vermeer C, et al. Uncarboxylated matrix Gla protein (ucMGP) is associated with coronary artery calcification in haemodialysis patients. Thromb Haemost 2009;101:359–66. [9] Cranenburg EC, Koos R, Schurgers LJ, et al. Characterisation and potential diagnostic value of circulating matrix Gla protein (MGP) species. Thromb Haemost 2010;104:811–22.
Contents lists available at ScienceDirect
International Journal of Cardiology journal homepage: www.elsevier.com/locate/ijcard
Letter to the Editor
Circulating species of matrix Gla protein and the risk of vascular calcification in healthy women Geertje W. Dalmeijer a,⁎,1, Yvonne T. van der Schouw a,1, Elke J. Magdeleyns b,1, Cees Vermeer b,1, Sjoerd G. Elias a, Birgitta K. Velthuis c,1, Pim A. de Jong c,1, Joline W.J. Beulens a,1 a b c
Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, The Netherlands VitaK, Maastricht University, The Netherlands Department of Radiology, University Medical Center Utrecht, Utrecht, The Netherlands
a r t i c l e
i n f o
Article history: Received 25 July 2013 Accepted 19 August 2013 Available online 27 August 2013 Keywords: Matrix Gla protein Vascular calcification. CAC MGP CVD
Observational studies showed that high vitamin K intake is associated with reduced coronary artery calcification (CAC) and cardiovascular disease (CVD) risk [1,2]. These effects are thought to be mediated by increased activation of the vitamin K-dependent protein matrix-Gla protein (MGP) [3]. However, only few studies investigated the relation of different MGP species with CAC and none of these studies were performed in the general population [4]. The aim of this prospective study is to investigate the association between circulating MGP species and vascular calcification among healthy women. This study was performed in a prospective cohort of 571 women aged 57.3 (±5.2) years, described in detail elsewhere [5,6]. Baseline plasma MGP levels were measured by ELISA techniques [7]. Calcification was measured in the coronary arteries, aortic valve, mitral valve, and aortic arch by multi-detector computed tomography after 8.5 (±1.3) years of follow-up and graded as present or absent. CAC was present if Agatston score was ≥10. The calcification score was calculated as the sum of the calcified areas. Modified Poisson regression was used to estimate relative risks (RR) for the association between MGP and CAC. Multinomial logistic regression was used to estimate odds ratios (OR) for the association between MGP or vitamin K with calcified areas, since this is an ordinal outcome. ⁎ Corresponding author at: Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, STR 6.131, PO Box 85500, 3508 GA Utrecht, The Netherlands. Tel.: +31 88 7568050; fax: +31 88 7568099. E-mail address: [email protected] (G.W. Dalmeijer). 1 This author takes responsibility for all aspects of the reliability and freedom from bias of the data presented and their discussed interpretation. 0167-5273/$ – see front matter © 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijcard.2013.08.062
In this population, 43% had CAC, 22% aortic valve calcification, 11% mitral valve calcification and 62% aortic calcification. High desphosphouncarboxylated MGP (dp-ucMGP) concentrations, reflecting poor vitamin K status, were borderline significantly (p = 0.08) associated with more CAC (RRSD: 1.07; 95%CI: 0.99–1.15) and calcified areas with an ORSD of 1.49 (95%CI: 0.95–2.35, p = 0.09) for 4 calcified areas versus no calcified areas adjusted for age, follow-up time, smoking, BMI, blood pressure and HDL-cholesterol (Table 1). High total-uncarboxylated MGP (t-ucMGP) concentrations were borderline significantly associated with fewer calcified areas (ORSD(4 vs 0 areas) 0.63; 95%CI: 0.36–1.10, p = 0.10). However, circulating t-ucMGP was not associated with the presence of CAC (RRSD: 1.06; 95%CI: 0.98–1.16, p = 0.17). This was due to the presence of a nonlinear relation as indicated by a significant quadratic term (p = 0.03). Spline regression showed evidence of a U-shaped relation (p = 0.13) between t-ucMGP and coronary calcification with lower presence of CAC up to 3.2 nM, but increasing RRs at higher levels (Fig. 1). Circulating desphosho-carboxylated MGP (dp-cMGP) was not associated with calcification. After adjustment, high phylloquinone intake was not associated with the number of calcified areas ORSD(4 vs 0 areas) 1.14 (95%CI: 0.72–1.81, p = 0.57). However, high menaquinone intake was significantly associated with decreased odds of having four calcified areas. Per SD increase in menaquinone, the odds of having four calcified areas was 61% lower (OR 0.39; 95%CI: 0.21–0.74, p = 0.004; Table 1). Both high phylloquinone (βSD:−0.043; 95%CI: −0.070; −0.016) and menaquinone (βSD: −0.032; 95%CI: −0.059; −0.009) intake were associated with lower dp-ucMGP concentrations adjusted for age, BMI and smoking. This prospective study shows that high dp-ucMGP concentrations may be associated with higher risk of CAC and more calcified areas. High t-ucMGP concentrations seem to be associated with fewer calcified areas. Furthermore, high menaquinone intake was associated with fewer calcified areas and lower dp-ucMGP concentrations. A previous study in this study population showed that high menaquinone intake, but not phylloquinone, was associated with reduced CAC [1]. We now show that high menaquinone intake is also associated with fewer calcified areas. Phylloquinone intake, however, was not associated with calcification. These results are in line with previous observational studies on vitamin K intake in relation to CAC and coronary heart disease [1,2,8]
G.W. Dalmeijer et al. / International Journal of Cardiology 168 (2013) e168–e170
e169
Table 1 Relative risks (95%-CI) of circulating levels of MGP species with coronary calcification and odds ratios (95%-CI) of MGP species, menaquinone and phylloquinone with calcification among 571 post-menopausal womena. CAC
calcified areas 0
N = 249
dp-ucMGP Model 1c Model 2d t-ucMGP Model 1c Model 2d dp-cMGP Model 1c Model 2d phylloquinone Model 1c Model 2d menaquinone Model 1c Model 2d
N = 138
RRb
95%CI
1.06 1.07
0.99–1.13 0.99–1.15
1.08 1.06 1.01 1.01
1
2
N = 179
3
N = 165
4
N = 55
N = 22
ORb
95%CI
ORb
95%CI
ORb
95%CI
ORb
95%CI
1 1
1.33 1.28
1.00–1.76 0.95–1.72
1.33 1.25
0.99–1.79 0.91–1.71
1.50 1.47
1.06–2.13 1.02–2.12
1.49 1.49
0.98–2.26 0.95–2.35
0.99–1.18 0.98–1.16
1 1
0.89 0.84
0.70–1.13 0.65–1.09
1.20 1.08
0.94–1.55 0.83–1.41
1.14 1.02
0.81–1.59 0.72–1.46
0.75 0.63
0.44–1.27 0.36–1.10
0.93–1.10 0.92–1.11
1 1
1.27 1.22
0.99–1.64 0.94–1.59
1.43 1.33
1.09–1.86 1.00–1.76
1.13 1.05
0.78–1.63 0.71–1.56
1.09 1.07
0.65–1.83 0.61–1.86
1 1
0.83 0.83
0.66–1.04 0.66–1.06
0.95 0.94
0.75–1.21 0.73–1.21
0.84 0.83
0.60–1.19 0.59–1.18
1.17 1.14
0.75–1.82 0.72–1.81
1 1
0.86 0.88
0.69–1.08 0.69–1.11
0.90 0.93
0.71–1.14 0.72–1.20
0.93 0.94
0.67–1.29 0.67–1.32
0.35 0.39
0.20–0.64 0.21–0.74
MGP, Matrix Gla protein; dp-ucMGP, desphospho-uncarboxylated MGP; dp-cMGP, desphospho carboxylated MGP; t-ucMGP, total uncarboxylated MGP. a Modified Poisson regression model was used to estimate relative risks (RR) for the association between MGP species and presence of CAC. Multinomial logistic regression was used to estimate odds ratios (OR) for the association between MGP species or vitamin K intake with calcified areas. The group with one to four calcified areas was compared with the group without calcification in any area. b All RRs and ORs are expressed per SD of the mean. c Adjusted for age, follow up time. d Adjusted for age, follow up time, smoke habits, BMI, blood pressure and HDL-cholesterol.
We observed borderline significant associations between high dpucMGP concentrations and CAC and more calcified areas. This is in line with the results of our cross-sectional study showing a borderline
Fig. 1. Association between t-ucMGP circulating levels and relative risk of CAC modelled continuously using splines; RR(—) with 95%CI in grey.
significant association between high dp-ucMGP and high CAC [6]. Similarly, previous studies reported higher dp-ucMGP concentrations among patients with diseases characterized by vascular calcification [4]. However, in another cross-sectional study among healthy adults, no association between dp-ucMGP and CAC was found [8]. Because this form of MGP has very low affinity for deposited calcium salts, the influence of vitamin K intake is directly observed in the circulation. Previous studies have shown that dp-ucMGP could be a sensitive marker of vitamin K intake and status with low concentrations reflecting a high vitamin K status or intake [3]. In line with these studies [4] we found that low dp-ucMGP concentrations were associated with high phylloquinone and menaquinone intake. Altogether, these results suggest that low dp-ucMGP concentrations could explain the reduced risk of CAC with high vitamin K intake. Similar to high-risk populations [4], we found that low t-ucMGP levels were associated with more calcified areas. Due to the presence of a U-shaped relation between t-ucMGP and CAC we did not find an association using linear regression. However, similar to the association with number of calcified areas, spline regression also showed slightly lower RRs for CAC up to 3.2 nM t-ucMGP, which increased at higher concentrations. We assume that t-ucMGP mainly consists of phosphorylated ucMGP species. The phosphoserines equip the molecule with strong calcium-binding groups irrespective of its Gla content and this fraction has a strong affinity to bind to vascular calcifications, resulting in a decrease in the circulating levels of t-ucMGP. This explains the lower t-ucMGP concentrations at higher CAC [9]. Therefore, t-ucMGP may act differently in persons with or without calcification. A limitation of our study is that the dp-ucMGP and dp-cMGP levels were low compared to a healthy reference population [7]. This could be due to the possible degradation of MGP in our samples, because the samples were stored for a long time. However, we compared the levels with those measured previously [6] and found reasonable correlation coefficients of 0.67 for dp-ucMGP and 0.51 for t-ucMGP. We therefore assume that degradation of MGP did not substantially affect the ranking of individuals and did not systematically bias the associations we found. Taken together, high dp-ucMGP concentrations, reflecting a poor vitamin K status, may be associated with more calcification, which
e170
G.W. Dalmeijer et al. / International Journal of Cardiology 168 (2013) e168–e170
could explain the reduced CAC risk with high vitamin K intake. High t-ucMGP concentrations seem to be associated with fewer calcified areas. Acknowledgements This research was supported by a personal Dr. Dekker postdoctoral grant (2008 T062) from the Netherlands Heart Foundation (JW Beulens). The data collection of this study was financially supported by grant 2100.0078 from the Netherlands Organization of Health Research and Development. The authors declare to have no conflict of interest. Cees Vermeer is CEO of VitaK B.V., The Netherlands. There was no commercial funding involved. References [1] Beulens JW, Bots ML, Atsma F, et al. High dietary menaquinone intake is associated with reduced coronary calcification. Atherosclerosis 2009;203:489–93.
[2] Geleijnse JM, Vermeer C, Grobbee DE, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr 2004;134:3100–5. [3] Schurgers LJ, Cranenburg EC, Vermeer C. Matrix Gla-protein: the calcification inhibitor in need of vitamin K. Thromb Haemost 2008;100:593–603. [4] Theuwissen E, Smit E, Vermeer C. The role of vitamin K in soft-tissue calcification. Adv Nutr 2012;3:166–73. [5] Atsma F, Bartelink ML, Grobbee DE, et al. Reproductive factors, metabolic factors, and coronary artery calcification in older women. Menopause 2008;15:899–904. [6] Dalmeijer GW, van der Schouw YT, Vermeer C, Magdeleyns EJ, Schurgers LJ, Beulens JW. Circulating matrix Gla protein is associated with coronary artery calcification and vitamin K status in healthy women. J Nutr Biochem 2013;24:624–8. [7] Shea MK, O'Donnell CJ, Vermeer C, et al. Circulating uncarboxylated matrix gla protein is associated with vitamin K nutritional status, but not coronary artery calcium, in older adults. J Nutr 2011;141:1529–34. [8] Cranenburg EC, Brandenburg VM, Vermeer C, et al. Uncarboxylated matrix Gla protein (ucMGP) is associated with coronary artery calcification in haemodialysis patients. Thromb Haemost 2009;101:359–66. [9] Cranenburg EC, Koos R, Schurgers LJ, et al. Characterisation and potential diagnostic value of circulating matrix Gla protein (MGP) species. Thromb Haemost 2010;104:811–22.