"Negligible side effects" stood out to me because I remember reading in a few places [0] [1] that depriving oneself of Vitamin A can improve vision; but at a health risk. I've also heard that this is impossible. [2]. I wonder if these things are co-related somehow?

[0] -- https://www.physiology.org/doi/abs/10.1152/ajplegacy.1938.12...

[1] -- https://petapixel.com/2014/08/23/dietary-experiment-successf...

[2] -- https://petapixel.com/2014/08/25/retinal-neuroscientists-reb...