Vitamin A

Won't restore your sense of smell after COVID-19 — a dedicated RCT found no significant benefit. Not a standalone thyroid treatment; the thyroid benefit seen was only in combination with other nutrients alongside prescription medication. Not proven to prevent cancer relapse on its own — the cancer data here is about how vitamin A levels interact with vitamin D, not vitamin A supplementation alone. More is not better — excess vitamin A in pregnancy was linked to worse outcomes, not better ones.

• Excess vitamin A (hypervitaminosis A) is toxic — a large pregnancy study found high levels were associated with adverse neonatal outcomes, not just deficiency
• Fat-soluble vitamins accumulate in the body; unlike water-soluble vitamins, you cannot easily excrete excess vitamin A
• The intranasal vitamin A RCT for COVID smell loss showed no significant benefit — do not rely on it for post-COVID olfactory recovery
• Vitamin A supplements can interact with other fat-soluble vitamins (D, E, K) and medications — the cancer study showed vitamin A levels modify how vitamin D works, suggesting complex interactions
• Many products use 'vitamin A' as a marketing umbrella for retinoids, beta-carotene, and retinal — these are chemically different with different safety profiles