Dietary sources of vitamin K include kale, spinach, broccoli, and other leafy greens. Some dairy foods also contain vitamin K.
The investigators who carried out the study say that their findings “suggest vitamin K may be involved in the disablement process in older age.”
They describe their work in a paper that features in a recent issue of The Journals of Gerontology: Series A.
Previous studies have established links between vitamin K and long-term conditions that can raise the risk of mobility disability. These conditions include cardiovascular disease and osteoarthritis.
However, none of those earlier investigations had examined the relationship between vitamin K and mobility disability directly.
M. Kyla Shea is the new study’s first and corresponding author. She researches Vitamin K at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University in Boston, MA.
Shea explains that: “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.”
She and her colleagues believe that they are the first to evaluate the relationship between “vitamin K status and incident mobility disability” in older adults.
The new evidence builds on earlier studies that have associated low levels of circulating vitamin K with “slower gait speed and a higher risk of osteoarthritis,” Shea explains.
Mobility is fundamental to healthy aging
Researchers typically define mobility as the “ability to move independently” from one place to another.
Physical independence is integral to healthy aging and older adults’ quality of life. From being able to get out of bed to walking and climbing stairs, much of daily activity involves mobility.
A 2018 study that reviewed the available evidence suggested that around 30% of older adults have limited mobility.
The most common causes of mobility disability in older people are the onset of lung problems, arthritis, and other long-term conditions.
A common measure of mobility is the ability to walk and climb stairs.
Mobility and vitamin K status
Vitamin K is a group of fat-soluble compounds that have a similar chemical structure and are present in some foods. Phylloquinone is the main dietary form of vitamin K and is present mainly in leafy greens.
To assess vitamin K status, Shea and her colleagues measured two blood biomarkers: phylloquinone and uncarboxylated matrix Gla protein (ucMGP), a protein that requires vitamin K. They note that ucMGP in the blood “increases when vitamin K status is low.”
The data that they analyzed came from 688 women and 635 men in the Health, Aging, and Body Composition (Health ABC) Study. Around 40% of the participants were black, and their ages ranged from 70 to 79 years.
The Health ABC study assessed mobility every 6 months for a period of between 6 and 10 years. The participants attended clinics and also completed interviews on the phone.
The researchers defined mobility limitation as two consecutive 6-monthly reports of experiencing “any amount of difficulty either with walking a quarter of a mile or climbing 10 steps without resting.”
They defined mobility disability as two consecutive 6-monthly reports of experiencing “a lot of difficulty or inability” to complete the same walking and climbing challenge.
The analysis showed that the older people who were most likely to develop mobility limitation and disability were the ones with low blood levels of phylloquinone.
In particular, the researchers found that developing mobility limitation was almost 1.5 times more likely in those with low blood levels of phylloquinone compared with those who had sufficient levels.
In addition, the chance of developing mobility disability for those low in phylloquinone was almost double that of those with sufficient levels.
There was no clear relationship between either mobility limitation or disability with blood levels of ucMGP.
The results for men and women were largely similar.
The researchers call for further studies to confirm their findings and clarify the mechanisms that might link vitamin K to mobility.
“Because of our growing population of older people, it’s important for us to understand the variety of risk factors for mobility disability.”
M. Kyla Shea