A recent review found increased IDO activation (using K:T ratio as a surrogate marker) is associated with age and chronic inflammation in PWH.30 Moreover, in the IDOze study, increased IDO activation (higher K:T ratios) in VS-WWH was associated with worse objective and subjective sleep outcomes.22,23 Tryptophan dysmetabolism and increased IDO activation have also been linked to depression and neurodegenerative disorders.16,24,31,32. This evidence concerns the gene IDO1 and depressive symptom measurement.