Association of Vitamin K Status Combined With Vitamin D Status and Lower-Extremity Function: A Prospective Analysis of Two Knee Osteoarthritis Cohorts

Shea MK, Loeser RF, McAlindon TE, Houston DK, Kritchevsky SB, Booth SL · Arthritis Care & Research (Hoboken)

Runs the two vitamins together rather than separately, on the argument that vitamin-K-dependent proteins in joint tissue need both. In Health ABC, people sufficient in both plasma vitamin K (≥ 1.0 nmol/L) and 25(OH)D (≥ 50 nmol/L) had better Short Physical Performance Battery scores and faster gait over follow-up (p ≤ 0.002). In the OAI the same combined sufficiency, measured as dietary intake rather than blood, tracked with faster gait and quicker chair stands (p ≤ 0.029). The authors call for co-supplementation trials.

Population

Health ABC knee OA substudy (60% female, mean age 75, circulating vitamin K and 25(OH)D) with replication in the Osteoarthritis Initiative (58% female, mean age 61, intake by food-frequency questionnaire), followed 4-5 years

Intervention

Sufficient vitamin K status or intake combined with sufficient vitamin D

Comparator

Insufficiency in either or both

Limitations

Observational in both cohorts, with function rather than structure or pain as the outcome, and the two cohorts measure the exposure differently — circulating concentration in one, questionnaire intake in the other. Combined-sufficiency categories are defined post hoc from continuous measures.