Assessment of Health-Related Quality of Life and Biomarkers in Long COVID: A 12-Month Longitudinal Feasibility Cohort

<b>Background/Objectives</b>: Long COVID (LC) causes persistent symptoms, including fatigue, musculoskeletal (MSK) pain, and a lower quality of life. It is hypothesised that chronic low-grade inflammation in LC could impact bone, joints, and muscle microcirculation, but evidence is limited. Our aim is to assess health-related quality of life (HRQoL) and circulating inflammation, bone turnover markers (BTM), and vitamin D in LC individuals to explore their potential association with MSK function. <b>Methods</b>: Prospective longitudinal cohort; LC <i>n</i> = 45, well-recovered (WR) <i>n</i> = 40; 12 ± 2 months follow-up. Baseline and follow-up assessments included evaluations of HRQoL and pain-rating questionnaires, and blood analysis of inflammatory and bone turnover markers (BTM). <b>Results</b>: More females were in the LC group. LC reported significantly lower HRQoL compared to WR, with no change over 12 months. LC had higher vitamin D levels at baseline, median 29.46 ng/mL (23.75; 35.06) compared to WR 20.36 ng/mL (15.995; 27.65) (<i>p</i> = 0.0021). Both groups experienced significant increases in vitamin D after 12 months: WR median from 21.4 ng/mL (16.34; 27.89) to 29.58 ng/mL (25.33; 41.74), (<i>p</i> =< 0.001) and LC median from 32.695 ng/mL (23.665; 35.1) to 35.89 ng/mL (30.1; 41.2), (<i>p</i> = 0.0023). Pain rating showed LC also experienced more hand pain at baseline median 1 (0; 5), (<i>p</i> = 0.003). There were no differences between groups in BTM or cytokines over time. <b>Conclusions</b>: This feasibility cohort showed that LC is associated with a reduction in HRQoL and joint symptoms; however, no significant changes were observed in the inflammatory markers, indicating the need for ongoing monitoring. Future studies should explore MSK, muscle function via imaging, and ways to enhance musculoskeletal health and well-being.