The overall goal of this pilot randomized trial is to obtain necessary prerequisite data to conduct a randomized controlled intervention to test the effect of vitamin K supplementation on knee osteoarthritis progression and related functional decline. To address critical parameters required to design this larger RCT, we will conduct a double-blind, 2-armed, parallel-group intervention study, with a placebo run-in, in which 50 adults with mild to moderate knee OA and low baseline vitamin K status will be randomly assigned to 1 mg phylloquinone/day or matching placebo, and treated for 6 months. Specifically, we will: (1) compare the effects of 1 mg/day phylloquinone vs. placebo on the non-functional circulating form of MGP; (2) estimate rates of recruitment and retention, follow-up rates and reasons for loss to follow-up, response rates to questionnaires, adherence/compliance rates, and potential for site differences; and (3) determine the responsiveness of the Osteoarthritis Research Society International (OARSI)-recommended performance-based tests of physical function in adults with low vitamin K status and mild to moderate knee osteoarthritis. We will also obtain preliminary data on the distribution of MGP genotype at two clinical sites for effect size generation.

As of February 2025, based on attrition rate below what was initially expected, we revised our planned enrollment from 50 to 35, to achieve the original goal of 30 completers. This was approved by the study sponsor.

Inclusion Criteria:

• Age ≥ 50 years
• Male or post-menopausal female (no menses in the last year)
• Plasma phylloquinone <1.0 nmol/L
• Chronic knee discomfort based on affirmative response to the question "During the past 12 months, have you had pain, aching, or stiffness in or around your knee(s) on most days for at least one month?"
• Kellgren-Lawrence (KL) grade 2-3 in at least one knee
• Ability to understand study procedures and to comply with them for the entire length of the study
• Ability to answer questions by phone
• Ability to swallow capsules

Exclusion Criteria:

• KL grade 4 in at least one knee
• Inability to walk
• Cognitive impairment (based on a Montreal Cognitive Assessment Test score ≤ 17)
• Widespread pain
• Malabsorption disorders (e.g. advance liver disease, stage 4 or 5 chronic renal disease, Crohn's disease, celiac sprue)
• Serious medical conditions or impairments that, in the view of the investigator, would obstruct study participation
• Plan to permanently relocate from the greater Boston, MA or Chapel Hill NC areas during the trial period
• Planned knee or hip arthroplasty during the study period
• Undergoing cancer treatment
• < 50 years old
• Circulating phylloquinone ≥ 1.0 nmol/L
• Warfarin (Jantoven) use
• Use of other investigational drugs
• Use of herbal, botanical or vitamin K supplements
• Use of assistive walking devices