Positives

• Cod liver oil (a natural source of vitamin A plus omega-3s) is highlighted in functional-medicine and Long COVID protocols as a foundational supplement combining mucosal repair with anti-inflammatory lipid support RTHM.
  
  

Negatives

• Patients hospitalized with COVID who took vitamin A supplementation reported no benefit over standard care on outcome severity PMC.
• Patients with chronic intake above ~10,000 mcg/day commonly develop hypervitaminosis A, with reports of headache, hair loss, brittle nails, joint pain and progressive liver damage from fatty liver to fibrosis NIH LiverTox.

Hurdles & Side Effects

• Vitamin A has a narrow therapeutic window: it is fat-soluble and accumulates in the liver, so chronic intake above 10,000 IU/day risks hypervitaminosis A (liver damage, severe headaches, bone loss, skin peeling) — specialists test serum retinol before high-dose supplementation NIH ODS.