This 2019 US review subject was β-glucan:
“β-1,3-Glucans (hereafter referred to as glucan) are natural molecules able to significantly improve our health. In human studies, the tested (and suggested) daily dose remains in the range of 100–500 mg for stimulation of the immune system, whereas for a decrease in cholesterol levels a daily dose of 3 g is recommended.
Glucan does not represent essential nutrients, but it might be successfully used not only for improvement of immune functions but also to improve the general quality of life via improvements of immune status, lowering cholesterol, improving blood glucose levels and reduction of stress. ClinicalTrials.gov summarizes 177 [now 199 with 103 completed] β-glucan clinical trials, mostly in cancer, gastrointestinal tract therapy, lowering cholesterol and improvements of immune reactions.
The question is not if glucans will move from food supplement to widely accepted drug, but how soon.
Reactions known to be influenced by glucan are represented in white, reactions where glucan has no confirmed effects are shown in black. The first defensive body response to infection results from formation of the anorexia cytokines (IL-1, IL-6, IL-8, and TNF-α).”
https://www.mdpi.com/1420-3049/24/7/1251/htm “Beta Glucan: Supplement or Drug? From Laboratory to Clinical Trials”
The review is also indexed at https://www.betaglucan.org/i-p/ under “Immunomodulator”
I’m curating this review on Day 12 of a self-quarantine after coming back from Milano, Italy, Monday, February 24, 2020. The previous Friday into Saturday I flew to Milano sitting with a group of elderly Italians who were returning from vacation.
On Saturday my wonderful woman and I used the Milano rail and subway system to go downtown. On Sunday we used the rail, bus, and ferry systems to visit Como, Bellagio, and Menaggio. I don’t think we could have mixed in more with people during transits, touristing, and Carnevale celebrations.
After returning to our hotel Sunday evening, we heard about the coronavirus outbreak south of Milano and the closing of ten towns. We changed flights and departed for the US early Monday morning.
Neither of us have had any signature symptoms of COVID-19 (fever, shortness of breath, dry cough). Our daily diet the past few years included β-glucan from steel-cut oats (~3 g) and from a 1/3, 1/6 yeast supplement (400 mg).