While we exit the COVID-19 pandemic, we are still feeling the effects of this virus. Many individuals have long COVID neurological symptoms which can include brain fog, sleep disturbances, depression and/or anxiety. ISTRY has followed COVID-19 research and how tryptophan metabolism is altered in both acute- and long-COVID (reported in our first newsletter and in our Featured Article series – see 2022 Aug, 2023 Jul, Oct, Nov). A recent study published by Dr. Mario Gietl and colleagues followed COVID patients over a year after being hospitalized with acute COVID-19 infection to assess the long-term effects.
At the initial visit kynurenine (KYN) and kynurenine/tryptophan (KYN/TRP) ratio was elevated in both sexes. Furthermore, KYN levels were significantly increased in individuals that had severe COVID when compared to those with moderate COVID. At one-year post-COVID, 31% of patients reported fatigue and 46% had sleep disturbance, demonstrating the long-effects that impact everyday life. Fifty percent or more of the female patients reported neurological symptoms, fatigue, and sleep disturbance at their one-year follow-up visit. Interestingly, individuals that reported sleeping disturbances at one-year post-COVID had higher KYN and KYN/TRP ratio than individuals without sleeping issues. Brain kynurenic acid (KYNA) increases have been shown to result in sleep disturbances (KM Rentschler et al., 2023) suggesting that the kynurenine pathway (KP) and elevated kynurenine levels may drive the long-term sleep disturbances in COVID-19 patients. Given this, inhibiting the KP may limit the effects of long-term COVID-19.