Study findings support an association between low blood levels of vitamin K and an increased prevalence of hand and knee osteoarthritis - the most common form of arthritis, occurring mainly at older ages, in which the cartilage cushioning the joints breaks down over time, leading to pain, stiffness and, often, limited mobility.

“We are not yet sure if vitamin K is in fact the cause of osteoarthritis,” lead author Tuhina Neogi, from Boston University, told Reuters Health. “But what we did see is that the lower the levels of vitamin K in the blood, the higher the prevalence of osteoarthritis.”

The primary form of vitamin K in the diet is “phylloquinone,” which is found mostly in green leafy vegetables, but also in cheese, liver, coffee, and green tea, for example. Insufficient intakes of vitamin K are not uncommon in the US and have already been shown to cause problems of blood coagulation in humans, according to Neogi.

“It’s a new hypothesis that vitamin K might be linked to osteoarthritis,” said Neogi. “In animals models, there are some bone and cartilage proteins known to be vitamin K dependent. When those proteins don’t work properly, the animals get a lot of bone and cartilage abnormalities, which resemble osteoarthritis.”

Working with over 650 participants, the researchers set out to determine whether vitamin K deficiency is associated with features of osteoarthritis on x-ray examinations.

Results, published in the journal Arthritis and Rheumatism, showed that patients with the lowest phylloquinone plasma levels were also the ones whose x-rays most often revealed the presence of large osteophytes, or “bone spurs” - small outgrowths of the bone common in arthritis.

“If there is a causal relationship between the two, the levels required for adequate functioning of vitamin K-dependent bone and cartilage proteins are not yet known,” Neogi said.

SOURCE: Arthritis and Rheumatism April 2006.