Vitamin K, a nutrient found in leafy greens and vegetable oils, might have protective health benefits as we age, researchers say in a new study.


Vitamin K is important for maintaining healthy blood vessels. It is found in leafy greens, such as lettuce, kale and spinach, and in some vegetable oils, especially soybean and canola.


The study, led by scientists at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University and at Tufts Medical Center, looked at 4,000 people ages 54-76, a third of whom were not white.


Researchers categorized participants according to their blood levels of vitamin K, then compared the categories for 13 years to determine the risk of heart disease and risk of death.


They combined data from participants in three ongoing studies: the Health, Aging, and Body Composition Study; the Multi-Ethnic Study of Atherosclerosis; and the Framingham Heart Study (Offspring Cohort).


For all three studies, vitamin K levels were measured after fasting and processed at the same laboratory, minimizing the potential for laboratory-based variation.


Although the results showed no significant associations between vitamin K levels and heart disease, Science Daily wrote, the people with the lowest vitamin K levels had a 19% higher risk of death compared to the those with vitamin K levels that reflected adequate vitamin K intake.


"The possibility that vitamin K is linked to heart disease and mortality is based on our 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," said first author Kyla Shea, a scientist on the HNRCA's vitamin K team.


Study co-author Daniel Weiner, a nephrologist (kidney doctor) at Tufts Medical Center, compared arteries to rubber bands.


"Similar to 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. That is why measuring risk of death, in a study such as this, may better capture the spectrum of events associated with worsening vascular health."


Although the study adds to existing evidence that vitamin K may have protective health benefits, "it can't establish a causal relationship between low vitamin K levels and risk of death because it is observational," Science Daily wrote.


More studies are needed to clarify why circulating vitamin K was associated with risk for death but not heart disease, the researchers said.


The same team found last year that "low levels of circulating vitamin K are linked to increased risk of mobility limitation and disability in older adults."


According to Shea last year: "Low vitamin K status has been associated with the onset of chronic diseases that lead to disability, but the work to understand this connection is in its infancy. Here, we're building on previous studies that found that low levels of circulating vitamin K are associated with slower gait speed and a higher risk of osteoarthritis."