[paulirwin]

I appreciate your respectful skepticism. It is entirely possible that the supplements contained significantly more than on the label. However, I'd like to point out that the generally recommended dose for supplements is only 800IU in adults, with up to 4000IU only in the case of Vitamin D deficiency. The "tolerable upper intake level" is 4000IU [1]. I am unable to track through Wikipedia's sources here at the moment, but that aligns with the parent of my original comment which I believe is in a peer reviewed journal. I would imagine that number was determined due to people like myself not tolerating amounts above 4000IU.

1: https://en.wikipedia.org/wiki/Vitamin_D#Dietary_intake

[mixmastamyk]

The original RDA of 800 was designed to combat Rickets and has recently been thought to be significantly too low for folks in higher latitudes. Given the high number of variables perhaps simple RDA guidelines are not practical.

I take roughly 5k per day in the winter and it has helped a lot. See my other post for details.