Diet lacking vitamin K1 makes knee joint susceptible to arthritis
If you don't consume much vitamin K1 [structural formula below] you are much more likely to develop arthritic knees than if you eat spinach, broccoli or other sources of vitamin K1 regularly. American nutritionists have written about it in the Journal of Medicine.

The researchers studied almost 1200 men and women aged between 50 and 79 who had osteoarthritis in their knee. They assessed the state of the participants' knee joints using MRI and radiography, and measured the concentration of vitamin K1 in their blood. According to current guidelines, if the vitamin K1 concentration is lower than 0.5 nanomoles there is a deficiency.Results
The MRI scans showed that participants whose vitamin K1 concentration was lower than 0.5 nanomoles had a higher incidence of damaged cartilage in their knee joint. A deficiency of vitamin K1 doubled the likelihood of damage.

The MRI scans also showed that the participants with too little vitamin K in their blood were more likely to have osteophytes – or growths – in their knee joints. But this relationship was not statistically significant.
A shortage of vitamin K1 increased the likelihood of osteoarthritis in the joint, and this was visible on the X-rays. Here there was also a doubling of the chance of osteoarthritis developing.

"There is a plausible rationale for the association of vitamin K with osteoarthritis", the researchers wrote.

"Vitamin K acts as an essential co-factor for the process of gammacarboxylation of Gla proteins, thereby conferring functionality to vitamin K-dependent Gla proteins. The bone and cartilage Gla proteins, such as MGP, osteocalcin, and Gas-6, play an important role in regulation of mineralization in these tissues, and the absence of functional forms of these proteins results in changes that are similar to those that occur in osteoarthritis."

The researchers refer to animal studies in which mice that produce no MGP die at a few months because their tissues calcify. [Nature. 1997 Mar 6;386(6620):78-81.] In in-vitro studies cartilage cells calcify less quickly if MGP is present in large quantities. [J Cell Biol. 2001 Aug 6;154(3):659-66.]
Vitamin K1 is found mainly in green vegetables, of which we consume less and less. The table below, taken from a 2012 review article [Food Nutr Res. 2012;56.], shows the best nutritional sources of vitamin K1. Top of the list is collards.

Of course there are also vitamin K supplements available. Many of these contain forms of the vitamin – the vitamin K2 variants – that have a higher bioavailability than vitamin K1. Before you start using these though, check out the side effects. Vitamin K plays a role in blood coagulation.

Am J Med. 2013 Mar;126(3):243-8.