Methods: A systematic review was conducted according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines searching the PubMed database. Eligibility for inclusion were original human studies evaluating the impact of COVID-19 on male reproductive health. Specific outcomes required for inclusion were at least one of the following: i) seminal detection of mRNA virus, or evaluation of ii) semen analysis, iii) testicular histology or ultrasonography, iv) testicular clinical symptoms and/or v) male reproductive hormones in COVID-19-positive patients.

Results: Of 553 retrieved articles, 25 met the inclusion criteria. This included studies primarily investigating the presence of viral RNA in semen (n = 12), semen quality (n = 2), testicular histology (n = 5), testicular pain (n = 2) and male reproductive hormones (n= 4). Results show little evidence for the presence of viral RNA in semen, although COVID-19 seems to affect seminal parameters, induce orchitis, and cause hypogonadism. Mortality cases suggest severe histological disruption of testicular architecture, probably due to a systemic and local reproductive tract inflammatory response and oxidative stress-induced damage.

MAIN BODY: This review (a) summarizes the effects of carnitines on female fertility along with the findings from various in vivo and in vitro studies involving human, animal and assisted reproductive technology, and (b) proposes their mechanism of actions in improving female fertility through their integrated actions on reducing cellular stress, maintaining hormonal balance and enhancing energy production. They reportedly aid β-oxidation in oocytes, maintain its cell membrane stability by acetylation of phospholipids and amphiphilic actions, prevent free radical-induced DNA damage and also stabilize acetyl Co-A/Co-A ratio for adequate acetyl storage as energy supply to maintain the robustness of reproductive cells.