These guys say it's a certain strain of gut bacteria that causes Parkinson's: https://yle.fi/a/74-20030498 https://yle.fi/a/74-20030498 The immune system decl

These guys say it's a certain strain of gut bacteria that causes Parkinson's: https://yle.fi/a/74-20030498 https://yle.fi/a/74-20030498 The immune system declines in old age and it migrates from the gut to the brain. Certain groups of gut bacteria like different nutrient environments, so the gut bacteria from this study might like that environment too.