60 hours awake, is this possible?

Two of my friends have decided to do sixty hours without sleeping. I wasn’t particularly worried about them since they’d done fifty hours before without any major side effects. But this morning I was with them and another friend. He brought up the fact that sixty hours would do major damage to their immune systems and they wouldn’t have the access to vitamin D since it’s now winter and last time they did this was in summer where it was plentiful.

Is sixty hours as much of an impact as my friend says it will compared to fifty hours? How long would it take for them to recover? Any advice?