Older adults with low levels of vitamin K had a higher risk of death over a 13-year period than those with adequate levels, a new multi-ethnic study has found. The findings suggest that vitamin K may have a protective effect on the health of older adults, the researchers said. Vitamin K is a nutrient found in green leafy vegetables and vegetable oils.
The meta-analysis involved nearly 4,000 Americans between the ages of 54 and 76, a third of whom were not white. The study, published monthly in the American Journal of Clinical Nutrition, was led by Jean Mayer of the USDA human Nutrition Aging Research Center and tufts Medical Center at Tufts University.
The team grouped participants according to their blood levels of vitamin K. They then compared the risk of heart disease and death for each group over a 13-year follow-up period.
The results showed no significant association between vitamin K levels and heart disease risk. However, those with the lowest levels of vitamin K had a 19 per cent higher risk of death than those with adequate vitamin K intake. Vitamin K is an important nutrient for vascular health. It is found in leafy greens such as lettuce, kale and spinach, and in certain vegetable oils such as soybean and rapeseed oil.
Lead author Keira Shay said: ‘We know that vitamin K is needed for proteins in vascular tissue to function and the idea that vitamin K may be associated with heart disease and mortality is based on this knowledge. Proteins in the blood help stop calcium buildup in the artery walls. If you don’t get enough vitamin K, these proteins won’t function properly.”
Shea is part of the Vitamin K team at the Human Nutrition Aging Research Center. The team is leading research on vitamin K to prevent chronic diseases. Study co-author Sara Booth, director of the Human Nutrition Aging Research Center, developed a way to measure vitamin K levels in the blood. Her team measured the subjects’ vitamin K levels and will continue to generate data on vitamin K in population and clinical studies.
“Just like a rubber band loses elasticity as it ages, when veins and arteries calcify, they pump less efficiently, leading to multiple complications,” said Co-author Daniel Weiner, a kidney specialist at Tufts Medical Center That’s why measuring the risk of death in studies like this can better determine what conditions are associated with deteriorating vascular health.”
Although this study adds to the existing evidence that vitamin K may have a protective effect, it cannot establish a causal relationship between low levels of vitamin K and the risk of death because the study is observational. Additional research is needed to clarify why blood levels of vitamin K are associated with a risk of death rather than heart disease.
The study is a meta-analysis, combining data from three ongoing studies, the report said. The three studies are the Health, Aging and Body Composition Study, the Multiracial Atherosclerosis Study and the Framingham Heart Study. Participants in all three studies measured vitamin K levels after fasting and in the same lab, the Vitamin K Lab at the Human Nutrition Aging Research Center, to minimize laboratory-based differences. The test showed the amount of vitamin K1 in the blood.
Participants using the blood thinner Warfarin were excluded because vitamin K reacted with the anticoagulant effects of warfarin. None of the participants had heart disease at the start of the study, and vitamin K levels were measured during only one physical exam, as part of the routine for each study.
The statistical analysis adjusted for age, sex, race, race, body mass index, triglycerides, cholesterol levels, smoking status and medication for diabetes or hypertension.
The study had some limitations, including the fact that blood vitamin K1 levels were measured from a single blood draw, rather than multiple blood tests. High levels of vitamin K1 may reflect better diet and lifestyle habits overall. Finally, fewer of the participants had heart disease compared to total deaths, which may have limited the researchers’ ability to identify statistically significant heart disease risks.