Conclusions

The age-associated diseases that appear to be most associated with severe COVID-19 are also associated with elevated IL-6 and other inflammatory markers, along with evidence of microbiome dysbiosis and/or low-grade infection. The imbalances in the immune system arising from this potentially microbiome-related inflammation are possibly a contributing factor in the susceptibility to acute viral infection and the severe cytokine storms that frequently lead to fatal outcomes in COVID-19.
In the long run, determination of how to achieve an optimal response to viral infections like COVID-19 will likely benefit from increased studies on how the microbiome might be shifted toward a more normal, healthy, youthful state. Based on the research discussed above, this state would be expected to be associated with a lower likelihood of severe effects from COVID-19 and other infectious agents, along with benefit in other debilitating diseases. It would be preferable to achieve this state with lifestyle and dietary factors; however, medications, probiotics and other approaches discussed in this review could also be used if supported by adequate research. To achieve this goal and the goal of improving COVID-19 outcomes, more research is clearly needed.