I think it depends on the Cfer.
I take vitamins every day. I was dignosed at the age of 2 and half years having the mutation Delta 508, which also meant I was pancreatic insufficient. So I have been on vitamins since I was a child because I was suffering from malutrition (as baby had the pot stomach thing going on, back there)lol.
Still they Doctors never put me on vitamin D til they found I was low at the age of 18 (when I transfered to adult hospital.) My dietitian said I had been low in vitamin D for a few years.
Since then, I have always found it a struggle to get my vitamin D levels up. Even with the Vitamin D supplement the Dietitian gave me at 18. So I have deciede on using trim milk with extra vitamins D and C in it.
Also I (on a different note) I find taking Flaxseed oil capsule 1000mgs, 2 times a day, has greatly helped my lungs. As we cfers often digest our essential fatty acids.
Hope this helps <img src="i/expressions/face-icon-small-smile.gif" border="0">
Now 27yrs w/c.f mutation DF508