I not only look at footnotes, I check out references themselves.
GreenMedInfo (a highly credulous and misleading source of medical “information”) loves to tout test tube and animal studies (as well as a few cherry-picked human trials) to support its claims that “natural” foods/supplements can prevent/cure just about anything.
Its citation of a Czech study suggesting an Echinacea drink treated flu as well as a prescription flu medication might be taken with a grain of salt (probably tastier than the drink), seeing that Echinacea has repeatedly shown to be of no or dubious value in preventing or treating respiratory infections including influenza. I find it interesting that sources like GreenMedInfo (which typically dismiss legitimate medical research on the grounds that, y’know, Big Pharma), would have no problem with a study that was paid for by the Echinacea drink maker, and even co-written by an employee of the company!
“This study was sponsored by A. Vogel Bioforce AG, Roggwil, Switzerland, manufacturer of Echinaforce Hotdrink. R. Schoop is an employee of Bioforce AG, and K. Rauš and P. Klein have received honorarium funds from the study sponsor. The authors have indicated that they have no other conflicts of interest regarding the content of this article.”
To put it simply, vitamins C and D seem to be of no real value in preventing colds and flu, unless one is badly deficient in them (very unlikely if you eat a halfway decent diet). Even the NIH’s own division on complementary medicine (which bends over backwards to find some use for alt med) recognizes that influenza vaccination (limited as its effectiveness can be in some years) is by far the best way to prevent flu.