Introduction: Rheumatoid arthritis (RA) is characterised by episodic flares of disease activity with increased levels of inflammation and functional limitations. Treatments involve corticosteroids which compound the catabolic environment of an RA flare. Essential amino acids (EAAs) can initiate anabolic effects and could be a useful intervention for maintaining muscle health in RA patients experiencing a flare.

Aims: The aims of this investigation were, i) to investigate muscle health changes following an RA flare, and ii), to assess the efficacy of EAA supplementation in mitigating muscle health deterioration in this cohort.

Methods: This randomised controlled trial (NCT06400316), conducted in collaboration with Leeds Teaching Hospital Trust, recruited 16 patients who were randomised to standard care (n=8) or a 4-week intervention (n=8) consuming 2 EAA supplements per day. A thorough assessment of muscle health (mass, quality, strength and function) was conducted at baseline, 2- and 4-weeks. Other data collected included disease activity scores, patient-reported outcome measures, physical activity, and dietary recall. Blood samples were collected and analysed for plasma amino acid concentrations and vitamin D3. Generalised Estimating Equations (GEE) determined between-group differences in all outcome measures. Spearman’s rank correlation tests were used to identify associations between variables, and linear regression was used to determine predictive validity of outcome measures against each other. All experimental procedures were conducted in accordance with the Declaration of Helsinki.

Results: Short Physical Performance Battery (SPPB) (p = 0.017) and 6-minute walk test (p = 0.014) performance were both significantly improved in the intervention group above that of the control group. Muscle mass was maintained in both groups with no significant differences between groups. Regression analysis revealed that muscle quality indices (pennation angle) and rectus femoris cross-sectional area significantly predicted improvements in muscle function (SPPB; p = 0.022, p = 0.02, respectively).

Conclusion: EAA supplementation significantly improved muscle function in RA patients experiencing a flare compared to standard care. Implementation of EAA supplementation alongside standard care should be considered in RA patients to mitigate the deterioration in muscle health during a disease flare.