Any vitamins left in slow-cooked veg?

[IcouldstillbeJoseph]

If I'm doing a casserole or similar I tend to throw the whole lot into the slow cooker and hope for the best. However, a friend of mine has just told me that if you cook veg etc for that long they no longer contain any 'good stuff'?
Wise mumsnetters, advise me.....

If the vitamins do escape from the veg, they'll end up in the sauce they're cooked in I reckon. Vitamins don't ascend to heaven when veg has been boiled to buggery.

Well I thought similar, but apparently hearing for that long destroys them?!

A quick Google threw up this, I have no idea of its accuracy..

www.beyondveg.com/tu-j-l/raw-cooked/raw-cooked-2e.shtml

'avoiding overly long cooking times'