How long can a human live without sunlight?

I'm not sure either. According to drug company promotions, vitamin D is essential and I don't believe D was available 90 years ago, but a few of the prisoners lived 70 years or more in prison. Florescent lights have been used for lighting in many prisons for about 70 years, and some of the tubes give a bit of exposure similar to sunlight, so perhaps this was sufficient. Incandescent bulbs produce almost no D except photo flood bulbs which operate at a higher temperature. In recent years vitamin D has been in most multi vitamins and has possibly been an additive in the food at some prisons. Massive amounts of D, are sometimes given right after a heart attack or stroke with good results. Eskimos living inside the Arctic Circle experience many consecutive days without any sunlight. Perhaps this is the reason very few live within 1000 kilometers of the North Pole. The bottom line is apparently humans can live without sunlight, but it probably is not healthy, and definitely tends to produce depression. Neil

that's a very generic question. you can't just say cause there are hundreds of variables... under normal circumstances (and most importantly if he is a mature adult when going under for ever) he would live as much as he would with light, given he has a way to get vitamin D.

Supermax prisoners in many US prisons never see but a slice of the sky for an hour a day or less. Sometimes the sun is shining down into the narrow exercise area, but most times it is not. And that is for life for some.