What to take for immune function
Graded by the strength of the evidence — strongest first. Nothing here is sold to you.
Probioticsgrade B— Cochrane systematic review of RCTs: probiotics reduced the number of people experiencing acute upper respiratory tract infections and shortened illness duration versus placebo, though the evidence was of low-to-moderate quality and heterogeneous.
Vitamin Dgrade C— modest reduction in acute respiratory infection risk, concentrated in deficient people
Ashwagandhagrade D— Review: ashwagandha shows immunomodulatory effects in mechanistic and early studies, but clinical evidence that it meaningfully improves immune outcomes in people is preliminary.