I think that Jody Powell is being hyper alarmist!

There are many supplements that have other uses, and as long as one follows sensible dosing guidelines, there is potential benefit. I have always felt people who "mega" dose are being irresponsible

As the 2nd link for Cod Liver Oil (which I also grew up with) is WebMD - here is their take on Vit D3 Cholecalciferol (Vitamin D3) Oral: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing - WebMD

PS I have also seen some articles that suggest Cod liver oil is dangerous now due to all the toxic stuff in the oceans, so one really does need to keep all this in balanced view IMO