A higher intake of K2, but not K1, was associated with a 20 per cent reduction in calcification of the arteries, according to findings published in the journal Atherosclerosis.
“This study shows that high intake of menaquinone [K2], but probably not phylloquinone [K1], is associated with reduced coronary calcification. Adequate intakes of menaquinone could therefore be important for the prevention of cardiovascular disease,” wrote lead author Joline Beulens from the University Medical Center Utrecht.
The study, which examined the dietary habits and cardiovascular health of 564 post-menopausal women, adds to a growing body of science linking the vitamin to improved heart health.
However, as the researchers state, results have been inconsistent, potentially due to “different effects of phylloquinone and menaquinone on coronary calcification”, they said.
Atherosclerosis, known as hardening or furring of the arteries is a key risk factor for cardiovascular disease, the cause of over 50 per cent of deaths in Europe and the US.
Beulens and co-workers assessed the diets of the 564 women (average age 67, average BMI 26.7 kg per sq. m) using a 77-item food frequency questionnaire (FFQ). A technique called multi-detector computed tomography (MDCT) was used to assess levels of arterial calcification.
The researchers report that the average intake of vitamin K1 was 217 micrograms per day, while vitamin K2 intakes averaged 31.6 micrograms per day for the whole study population.
Furthermore, 82 per cent of the K1 came from vegetables, while K2 came predominantly from cheese (54 per cent), milk products (22 per cent), and meat (15 per cent).
Based on the MDCT exam 62 per cent of the women had calcification of the arteries, said the researchers. When the intakes of K1 and K2 were divided into four groups from the lowest to highest, no association was found between K1 intakes and calcification. However, high consumption of K2 (about 45 micrograms per day) was associated with 20 per cent decreased coronary calcification, compared with low consumption of K2 (about 18micrograms per day).
Explaining the differences between vitamin K forms
The metabolism of menaquinone and phylloquinone was cited as the probable reason as to why the different forms of vitamin K showed different results with respect to calcification.
“Phylloquinone is predominantly transported with the triacylglycerol-rich fraction, which is mainly cleared by the liver. Phylloquinone is therefore very effectively cleared from circulation by the liver to function as a cofactor for proteins in blood coagulation,” wrote the researchers.
“Menaquinones, on the other hand, are found in both triacylglycerol-rich lipoprotein and low-density lipoprotein, which are equally transported to extrahepatic tissues,” they said. “Menaquinone could therefore more effectively influence MGP and coronary calcification.”
MGP (matrix Gla protein) is a regulator of calcium crystal formation in the circulatory system. MGP is a vitamin K-dependent protein - meaning vitamin K is required to activate this important protein.
Commenting on the study, vitamin K researcher Leon J Schurgers from VitaK at the Maastricht University in the Netherlands said: “This study confirms once again that natural Vitamin K2, also called the menaquinones, is clearly linked to the prevention of cardiovascular disease.”
“While all K vitamins are important, it seems that especially the natural vitamin K2 intake is essential to cardiovascular health,” added Schurgers, who was not involved in the Utrecht study.
The vitamin K family
Phylloquinone (vitamin K1) is found in green leafy vegetables such as lettuce, broccoli and spinach, and makes up about 90 per cent of the vitamin K in a typical Western diet.
Menaquinones (MK-n: with the n determined by the number of prenyl side chains) make up about 10 per cent of Western vitamin K consumption and can be obtained from different dietary sources. MK-4 can be found in animal meat, MK-7, MK-8, and MK-9 are found in fermented food products like cheese, and natto is a rich source of MK-7.
MK-4 is distinct from other MKs because it is not a major constituent of the spectrum of MKs produced by gut microflora, but can be derived from K1 in vivo.
A synthetic form of vitamin K, known as K3, does exist but is not recommended for human consumption.
Source: AtherosclerosisPublished online ahead of print, doi:10.1016/j.atherosclerosis.2008.07.010“High dietary menaquinone intake is associated with reduced coronary calcification”Authors: J.W.J. Beulens, M.L. Bots, F. Atsma, M.-L.E.L. Bartelink, M. Prokop, J. M. Geleijnse, J.C.M. Witteman, D.E. Grobbee, Y.T. van der Schouw