Subjects receiving a daily vitamin K1 plus multivitamin supplement experienced six per cent less progression of coronary artery calcification (CAC), or hardening of the arteries that leads to atherosclerosis and cardiovascular disease, people receiving only the multivitamin.
Researchers led by Sarah Booth from the USDA Human Nutrition Research Center on Aging at Tufts University write in the new issue of the American Journal of Clinical Nutrition that such benefits were independent of changes in levels of a protein called matrix Gla protein (MGP).
MGP 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 protein.
Speaking to NutraIngredients.com at the recent Vitafoods show in Geneva, vitamin K expert Professor Cees Vermeer from VitaK at the University of Maastricht explained that matrix Gla protein (MGP) in the vessel walls is a hot topic.
“It is the most powerful inhibitor of soft tissue calcification presently known, and it definitely needs the vitamin K to be active in that way. So, vessel walls have only MGP to defend themselves against calcification,” he said.
According to the new findings, however, supplementation with phylloquinone (500 micrograms per day) slowed CAC in older men and women independently of MGP.
There are two main forms of vitamin K: phylloquinone (vitamin K1) and menaquinones (vitamins K2). 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; while K2 makes up about 10 per cent of Western vitamin K consumption.
Menaquinones (MK-n: with the n determined by the number of prenyl side chains) can also be found in the diet; 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.
Booth and her co-workers recruited 388 healthy with evidence of CAC. The subjects were randomly assigned to receive vitamin K1 plus multivitamins or only multivitamins for three years. The supplements were manufactured by Munich-based Hermes Arzeneimittel GmbH.
Overall, no significant differences in the groups were observed. However, in people with pre-existing CAC who took at least 85 per cent of the assigned supplements experienced a retardation of CAC progression of 6 per cent, compared to the control group. Such decreases occurred independently of changes in serum MGP, said Booth and her co-workers.
“Vitamin K supplementation reduced the progression of existing CAC in asymptomatic older men and women when taken with recommended amounts of calcium and vitamin D. The mechanisms by which vitamin K conferred a protective role are still uncertain,” wrote the researchers.
“Larger studies in other populations are needed to confirm these findings, and to assess the risks and benefits of vitamin K supplementation on clinical CVD,” they concluded.
The study was supported financially by the US Department of Agriculture, Agricultural Research Service (USDA ARS), the National Institutes of Health (NIH), and the American Heart Association.
The other researchers were affiliated with Tufts University, the National Heart, Lung, and Blood Institute's Framingham Heart Study, Massachusetts General Hospital, and the University of California, San Diego.
Source: American Journal of Clinical Nutrition June 2009, Volume 89, Pages 1799-1807, doi:10.3945/ajcn.2008.27338 "Vitamin K supplementation and progression of coronary artery calcium in older men and women” Authors: M.K. Shea, C.J. O'Donnell, U. Hoffmann, G.E. Dallal, B. Dawson-Hughes, J.M. Ordovas, P.A. Price, M.K. Williamson, S.L. Booth