Vitamin K, a nutrient found in leafy greens and vegetable oils, may have protective health benefits as we age and directly affect longevity in older adults, a new multi-ethnic study has found.
Published in The American Journal of Clinical Nutrition, the study reports that older adults with low vitamin K levels had a higher risk of death over a 13-year period compared to those with adequate levels. The research was conducted by involving nearly 4,000 Americans aged 54-76, one-third of whom were non-white, and was led by a team at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University (USDA HNRCA) and Tufts Medical Center.
For the study, researchers categorised participants according to their vitamin K blood levels and then compared risk of heart disease and death across the categories over a period of 13 years.
Although the results showed no significant association between vitamin K levels and heart disease, people with the lowest vitamin K levels had a 19% higher risk of death, compared to those with levels that reflected adequate vitamin K intake. The results were adjusted for age, gender, race, ethnicity, body mass index, triglycerides, cholesterol levels, smoking status and the use of medications for high blood pressure or diabetes.
The meta-analysis for this research combined data from three ongoing studies, namely, ‘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 minimising 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.
Vitamin K is a nutrient that is important for maintaining healthy blood vessels, blood clotting, bone metabolism and regulating blood calcium levels. It is found in leafy greens, such as lettuce, kale, spinach, broccoli, cabbage, cauliflower, as well as parsley, among others, and in some vegetable oils, especially soybean and canola.
"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 Dr Kyla Shea, one of the lead scientists on the HNRCA team.
Dr Sarah Booth, a co-author on the study and director of the USDA HNRCA, developed the methodology for measuring vitamin K in blood. Her research team measured the vitamin K levels in the study participants and continues to generate data about vitamin K status in population and clinic-based studies.
"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 Dr Daniel Weiner, nephrologist at Tufts Medical Center, whose research includes vascular disease in people with impaired kidney function.
While this study adds to existing evidence that vitamin K may have protective health benefits, being a purely observational study, it does not establish a causal relationship between low vitamin K levels and risk of death. Additional research is required to clarify why circulating vitamin K was associated with risk for death but not heart disease.
