For an overarching theory, see the book: Microbial Burden: A Major Cause Of Aging And Age-Related Disease by by Michael Lustgarten. Also related: What if we fo

For an overarching theory, see the book: Microbial Burden: A Major Cause Of Aging And Age-Related Disease by by Michael Lustgarten. Also related: What if we found out that blood microbiome is the most significant marker of heart disease? E.g. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5328378/ https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5328378/