Vitamin K is a fat-soluble vitamin that comes in two forms.
The main type is called phylloquinone, found in green leafy vegetables like collard greens, kale, and spinach. The other type, menaquinones, is found in some animal foods and fermented foods.
The human body requires vitamin K for post-synthesis modification of certain proteins that are required for blood coagulation or for controlling the binding of calcium in bones and other tissues.
Recent studies have found that vitamin K is very important for health in older people.
In a study from Edith Cowan University, scientists found that people who eat a diet rich in vitamin K have up to a 34% lower risk of atherosclerosis-related heart disease (conditions affecting the heart or blood vessels).
They examined data from more than 50,000 people taking part in the Danish Diet, Cancer, and Health study over a 23-year period.
The team tested whether people who ate more foods containing vitamin K had a lower risk of heart disease related to atherosclerosis.
Atherosclerosis is the thickening or hardening of the arteries caused by a build-up of plaque in the inner lining of an artery.
The team found that people with the highest intakes of vitamin K1 were 21% less likely to be hospitalized with heart disease related to atherosclerosis.
For vitamin K2, the risk of being hospitalized was 14% lower. This lower risk was seen for all types of heart disease related to atherosclerosis, particularly for peripheral artery disease at 34%.
These findings suggest that consuming more vitamin K may be important for protection against atherosclerosis and subsequent heart disease.
The team says that the role of vitamin K in heart health and particularly in vascular calcification is an area of research offering promising hope for the future.
While databases on the vitamin K1 content of foods are very comprehensive, there is currently much less data on the vitamin K2 content of foods.
Furthermore, there are 10 forms of vitamin K2 found in the human diet and each of these may be absorbed and act differently within the body
The research was published in the Journal of the American Heart Association and conducted by Dr. Nicola Bondonno et al.
In another study from Université de Montréal, researchers found that food rich in vitamin K may benefit people who have blood clots and take the anticoagulant drug warfarin.
They found that patients on warfarin benefit from increasing their vitamin K intake, as long as they keep their intake levels consistent.
Warfarin is widely used to prevent dangerous blood clots that cause heart attacks and strokes.
The drug’s dosage must be carefully calibrated to balance the risk of clots against the risk of uncontrolled bleeding.
Because warfarin counteracts the activity of vitamin K in the blood, large swings in vitamin K intake can disrupt this balance.
Many patients using warfarin are told to limit foods rich in vitamin K, such as green vegetables.
In this study, researchers found that patients would be better advised to increase the amount of vitamin K in their diet. They tested 46 patients who took warfarin to prevent blood clots.
Half attended dietary counseling sessions and cooking lessons that provided general nutrition information, while half attended counseling sessions and cooking lessons focused on increasing the intake of green vegetables and vitamin-K-rich oils and herbs.
After six months, 50% of those counseled to increase their vitamin K intake were maintaining stable anticoagulation levels, compared with just 20% of those who received general nutritional counseling.
The researchers that patients taking warfarin would benefit from consuming foods that provide a minimum of 90 micrograms of vitamin K per day for women and 120 micrograms per day for men.
They say that given the direct interaction between dietary vitamin K and the action of the drug, it is important to have a higher daily vitamin K intake as consistent as possible.
The study was presented at the American Society for Nutrition annual meeting and conducted by Guylaine Ferland et al.
In another study from Tufts University, researchers found older people with low vitamin K levels were more likely to die within 13 years compared to those whose vitamin K levels were adequate.
The finding suggests vitamin K, a nutrient found in leafy greens and vegetable oils, may have protective health benefits as we age.
In the study, the team reviewed published research that tested nearly 4,000 Americans aged 54-76. The team categorized participants according to their vitamin K blood levels.
The team then compared the risk of heart disease and risk of death across the categories over approximately 13 years of follow-up.
They showed no strong associations between vitamin K levels and heart disease.
However, the people with the lowest vitamin K levels had a 19% higher risk of death, compared to those with vitamin K levels that reflected adequate vitamin K intake.
The team says that when a rubber band dries out and loses its elasticity when veins and arteries are calcified, blood pumps less efficiently, causing a variety of complications.
The possibility that vitamin K is linked to heart disease and mortality is based on the knowledge about proteins in vascular tissue that require vitamin K to function.
These proteins help prevent calcium from building up in artery walls, and without enough vitamin K, they are less functional.
The study was published in The American Journal of Clinical Nutrition and conducted by Kyla Shea et al.
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