Be like Popeye. Eat your spinach. And kale. And lettuce. That’s the takeaway from a recent multi-ethnic meta-analysis by researchers at Tufts University.
While the study didn’t prove cause and effect, it did show that the risk of death was nearly 20% higher for older adults with low vitamin K levels compared to those whose levels were adequate. The results suggest vitamin K, a nutrient found in leafy greens and vegetable oils, may have protective health benefits as we age, according to the researchers.
The meta-analysis involved nearly 4,000 Americans between the ages of 54 and 76. One-third of the participants were non-white. Researchers at the Jean Mayer USDA Human Nutrition Research Center on Aging (USDA HNRCA) and Tufts Medical Center categorized participants according to their vitamin K blood levels. They then compared the risk of heart disease and risk of death across the categories over approximately 13 years of follow-up.
The results showed no significant 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.
Vitamin K is important for maintaining healthy blood vessels. In addition to leafy greens, it’s also found in some soybean and canola oils.
The possibility that vitamin K is linked to heart disease and mortality is based on existing knowledge about proteins in vascular tissue that require vitamin K to function. These proteins help prevent calcium from building up in artery walls. Without enough vitamin K, they are less functional, according to first author Kyla Shea, a scientist on the HNRCA’s vitamin K team, which studies the role of vitamin K in the prevention of chronic disease.
“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 co-author Daniel Weiner, M.D., a nephrologist at Tufts Medical Center.
The meta-analysis, published in the May 2 issue of The American Journal of Clinical Nutrition, 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. Vitamin K levels for participants in all three studies were measured after fasting using the same test and processed at the same laboratory, which minimized the potential for laboratory-based variation. The test showed levels of circulating phylloquinone, the compound known as vitamin K1.
Participants taking the blood thinner warfarin were excluded because vitamin K counteracts the anti-clotting effects of warfarin. All participants were free of heart disease at baseline and had vitamin K levels measured during a single medical exam that was part of each study’s regular protocol.
The statistical analysis did adjust for age, gender, race, ethnicity, BMI, triglycerides, cholesterol levels, smoking status and use of medications for diabetes or high blood pressure.
Researchers note some limitations to the study, including that circulating phylloquinone was measured from a single blood draw, rather than from repeated blood tests over time. Higher circulating phylloquinone may reflect an overall healthier diet and lifestyle. Lastly, there were fewer heart disease events compared to total deaths, which may have limited researchers’ ability to detect statistically significant risk of heart disease.
Journalists may want to look at issues related to adequate nutrition in older adults. For example:
- High-quality produce can be scarce and expensive for people living in “food deserts.”
- During the pandemic, many older adults have been hesitant to venture out to supermarkets. They may be relying on food banks or volunteer services to deliver meals, which may not provide adequate levels of vitamins, minerals and other nutrients.
- Medications can also interfere with the absorption of key nutrients. What can be done to counteract this effect? Are supplements a good idea?