A high daily intake of vitamin K1, found in green leafy vegetables, could reduce the risk of fatal coronary heart disease by 19 per cent, says a new study.
But despite the impressive reductions for fatal CHD, the links with non-fatal heart attacks, strokes, and coronary heart disease in general were more indicative of a healthy dietary and lifestyle pattern rather than an independent risk reduction, said the researchers from Tufts University, Harvard School of Public Health, and the University of Kuopio in Finland.
"This finding is particularly important because the presence of phylloquinone is limited to a relatively narrow range of foods," wrote lead author Arja Erkkilä in the journal Nutrition, Metabolism and Cardiovascular Disease (doi: 10.1016/j.numecd.2006.03.008).
"Because there is an association between phylloquinone [vitamin K1] intake and both a healthy diet and lifestyle, in large population groups phylloquinone intakes may provide a more robust assessment of overall CHD risk status than assessing multiple individual diet and lifestyle habits."
Vitamin K is traditionally less well known than vitamins A to E, but this increasing body of research, as well as increased marketing and advertising from supplement makers, is raising public awareness of vitamin K.
There are two main forms of vitamin K: phylloquinone (vitamin K1) which is found in vegetables such as lettuce, broccoli and spinach, and makes up about 90 per cent of the vitamin K in a typical Western diet; and menaquinones (vitamins K2), which make up about 10 per cent of Western vitamin K consumption and can be synthesised in the gut by microflora.
For the most part, previous research has focussed on the role of vitamin K in boosting bone health. However, in a recent article, published in the journal Nutrition (Vol. 22, pp. 845-852), Masao Kaneki from Harvard Medical School, reviewed the evidence concerning atherosclerosis and cancer of the liver, and concluded that, based on current literature, it appears possible that vitamin K deficiency is associated with atherosclerosis and hepatocarcinoma.
The new study, published, used data from the Health Professionals' Follow-up Study that followed over 40,000 men. Dietary intake was assessed using a semi-quantitative food frequency questionnaire (FFQ). During the period 1986 to 2000, 1857 CHD events and 617 strokes were recorded.
The average intake of phylloquinone was 165 micrograms per day, and the highest intake group was consuming about 312 micrograms per day.
After adjusting for lifestyle factors, as well as dietary factors known to be associated with CHD risk, like saturated, polyunsaturated, and trans fat, and cereal fibre and folate intake, the researchers found that people in the highest intake group of vitamin K1 had an associated reduction in the risk of fatal CHD of 19 per cent.
The same adjustments for total CHD, and non-fatal heart attack resulted in associated reductions of nine and five per cent, respectively. However, this result was not considered significant by the researchers.
"Consistent with previous work, a high phylloquinone intake was associated with a dietary pattern and lifestyle recommended for cardiovascular disease prevention in men," wrote Erkkilä.
"There was a significant trend towards a lower risk of total CHD events in men who reported higher intakes of phylloquinone compared to those with lower intake."
No mention of the mechanism is reported by the researchers, but some evidence has reported that the potential cardiovascular role is be due to the presence of a vitamin K-dependent protein, MGP, in atherosclerotic plaque. Gene disruption of MGP is said to result in extensive calcification of the aorta.
Heart disease causes almost 50 per cent of deaths in Europe, and is reported to cost the EU economy an estimated €169 billion (£116 billion) per year.