It's hard ... very hard.  COVID-19 is burning through communities & nations and we currently don't have a vaccine or other obvious medical protection against it.  Interestingly age makes a difference.  Older people ... like me (I'm due to be 70 in a couple of weeks time) ... are more at risk of bad outcomes if we catch the virus.  And I bet that's more about 'biological age' than 'chronological age'.  As I wrote over 10 years ago in the post "Would you like to be 14 years younger - it's largely a matter of choice!", lifestyle (for example exercise, diet, weight, sleep & substance use) makes a huge difference to our health & life expectancy (including our likely response to COVID-19).  And as I've also written - see "Are dietary supplements a dangerous waste of money?" - healthy diet is so very much more important than the often dubious value of taking vitamin & mineral supplements. 

But assuming one is doing one's best with lifestyle behaviours, is there any potential benefit from taking any particular dietary supplements in response to the coronavirus threat (especially maybe for older people and others who are more vulnerable)?  Well McCarty & DiNicolantonio in their recent paper "Nutraceuticals have potential for boosting the type 1 response to RNA viruses including influenza and coronavirus"  certainly seem to think so.  They mention nine substances (and give some guide to doses) - ferulic/lipoic acids, spirulina, N-acetylcysteine, selenium, glucosamine, zinc, yeast beta-glucan, and elderberry.  Mm ... that's rather a lot to rush to stock up on and take regularly.  

N-acetylcysteine I know a bit about as it has been used quite extensively for mental health difficulties (much more my field of knowledge) - see, for example, "N-acetylcysteine for major mental disorders: a systematic review and meta-analysis of randomized controlled trials".  And more broadly, a book has recently been published on "The therapeutic use of N-acetylcysteine (NAC) in medicine".  NAC can clearly be helpful for viral diseases - see the impressive 1997 study "Attenuation of influenza-like symptomatology and improvement of cell-mediated immunity with long-term N-acetylcysteine treatment".  Although more recent research - "N-acetylcysteine: an old drug with variable anti-influenza properties" - shows that NAC seems beneficial in some viral infections but not others, we don't have the time to wait to see if NAC is or isn't helpful for COVID-19.  As a pretty safe dietary supplement, the suggested dosing of 600mg twice daily seems reasonable, although - as long as it's well tolerated - I would tend to start with a total of 1,800mg daily for the first month as the 1997 study only showed encouraging benefits in the second month of using a total of 1,200mg daily (so using a higher dose initially makes some sense).

Spirulina sounds interesting - see, for example "Well-tolerated Spirulina extract inhibits influenza virus replication and reduces virus-induced mortality".  However this supplement/dietary addition seems more tentative as far as application to coronavirus is concerned and the McCarty & DiNicolantonion recommended dose of 15gm daily seems quite high - see for example the range reported in the 2018 paper "Quantifying the effects of spirulina supplementation on plasma lipid and glucose concentrations, body weight, and blood pressure" .  I could give it a try though & see how I tolerate it.  Another recent review paper - "A review of micronutrients and the immune system - working in harmony to reduce the risk of infection" - particulary mentions vitamins C & D as well as zinc.  So in a bit of a haphazard way, I plan to try daily doses of the spirulina, N-acetylcysteine and vitamin D ... as well as a good multimineral/vitamin supplement containing selenium, zinc & vitamin C amongst other ingredients ... and use elderberry at early signs of feeling at all unwell - see last year's paper "Black elderberry (Sambucus nigra) supplementation effectively treats upper respiratory symptoms: A meta-analysis of randomized, controlled clinical trials".  Maybe clutching at straws, but at least the elderberry should provide reasonably pleasant tasting straws!