The meta-analysis involved close to 4,000 Americans between the ages of 54-76 who were categorized according to their vitamin K blood levels, then compared for risk of heart disease and death risk across the categories over a 13 year follow up.
Findings showed no significant associations between vitamin K levels and heart disease, but those with the lowest levels were found to have had a 19% higher risk of death compared to those with adequate levels. Findings were adjusted for age, gender, race, ethnicity, BMI, triglycerides, cholesterol levels, smoking status, and the use of medications for high blood pressure or diabetes.
Vitamin K is found within leafy green vegetables such as spinach, lettuce, Swiss chard, kale, collards, broccoli, cabbage, Brussels sprouts, cauliflower, as well as parsley among others, and the nutrient is important for maintaining healthy blood vessels, blood clotting, bone metabolism, and regulating blood calcium levels.
“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.
“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,” said last author Daniel Weiner, M.D., nephrologist at Tufts Medical Center, whose research includes vascular disease in people with impaired kidney function.
This study adds to evidence that vitamin K may have protective health benefits but is not able to establish a causal relationship between low levels and death due to the observational nature of the study; additional research is required to clarify the associations.
The meta-analysis combined data from three ongoing studies: The Health, Aging, and Body Composition Study, the Multi-Ethnic Study of Atherosclerosis, and the Framingham Heart Study (Offspring Cohort). Vitamin K levels were measured in participants in all of the studies after fasting with the same test, and were processed at the same lab minimizing the potential for variations. Participants were free from heart disease at baseline, and those on warfarin blood thinners were excluded as vitamin K counteracts the effects of the drug.
Limitations included circulating phylloquinone being measured from a single blood draw rather than repeated tests over time; higher levels could reflect an overall healthier diet and lifestyle; and there were fewer heart disease events compared to total deaths which may limit the ability to detect statistically significant risk of heart disease.
