Mayo Clinic: Debunking COVID-19 (coronavirus) myths. Extremely unlikely to work and might cause serious harm. [...] Supplements. Many people take vitamin C, vitamin D, zinc, green tea or echinacea to boost their immune systems. While these supplements might affect your immune function, research hasn't shown that they can prevent you from getting sick.

Notice the weird mind crinkle: Got to debunk it, and use "prevent you from getting sick" as the reason for it not working (and the subtle differences between: "No research has shown", "research hasn't shown", and "research has shown that it can't prevent you"). Even though plenty of research shows it prevents you from getting severely sick, when you do get sick. Willing to bet that garlic (a famous folk knowledge cure for the flu, smashed boiled garlic with hot water) is actually effective in recovery and severity, but the fact checkers present it as a "COVID cure" and of course that can be debunked. But it is a debunking based on a weird strawman we saw with masks: Masks are not protective to COVID because the eyes can catch it too. As if protectiveness and immune health is binary and anything else than 0 or 1 has to be a lie.

Could not find anything about the CDC, just https://www.cdc.gov/nutrition/infantandtoddlernutrition/vita... where they recommend Vitamin D for children under 2 years old, to prevent deficiency, but no where mention a recommendation for using it during a pandemic to keep your immune system healthy.

As for selenium deficiency and iodine deficiency, the research is slowly catching up:

> Certain micronutrients are seen as supportive for the treatment of and protection against viral diseases with some vitamins (A, B6, B12, C, D, and E) and essential trace elements (zinc, iron, selenium (Se), magnesium, or copper) discussed as particularly promising .

> However, the data base is very small and it is unknown whether certain vitamins or trace elements are deficient in patients with COVID-19, and whether the concentrations are related to disease severity or mortality risk.

> The collaborative research team from Germany hypothesised that Se may be of relevance for infection with SARS-CoV-2 and disease course of COVID-19 and that severe Se deficiency is prevalent among the patients and associates with poor survival odds in COVID-19.

As for turmeric, mentioned in relation to COVID a bannable offense on Youtube: It inhibits and suppresses Zika, Hepatitis, HIV, Noro, coxsackie, HBV, herpes, influenza, encephalitis, dengue, corona, and chikunya. It also suppresses cytokine signalling. But experts warn that it may interfere with the immune system when fighting COVID, and that it is neither a cure nor a treatment nor a helpful supplement. WHO lists it under hoaxes (except when discussing Chinese traditional medicine). And you are a bad person if you share this potential online, because you don't have a randomized trial to back up that it works against SARS-CoV-2.

MedicalNewsToday: In a rapid review of the evidence published on May 1, 2020, researchers from the Centre for Evidence-Based Medicine at the University of Oxford in the United Kingdom unequivocally conclude: “We found no clinical evidence on vitamin D in [the prevention or treatment of] COVID-19.” They also write that “[t]here was no evidence related to vitamin D deficiency predisposing to COVID-19, nor were there studies of supplementation for preventing or treating COVID-19.”

Potential Effect of Curcumin Treatment of COVID-19: Curcumin may have beneficial effects against COVID‐19 infection via its ability to modulate the various molecular targets that contribute to the attachment and internalization of SARS‐CoV‐2 in many organs, including the liver, cardiovascular system, and kidney. Curcumin could also modulate cellular signaling pathways such as inflammation, apoptosis, and RNA replication. Curcumin may also suppress pulmonary edema and fibrosis‐associated pathways in COVID‐19 infection.

WHO Fact or Fiction: There is no scientific evidence that lemon/turmeric prevents COVID-19.