Oooh, now that is very odd. I guess only your doctor would be able to advise as it sounds like there was some other concern there.
It's not usually advised to take extra vitamins whilst on Cambridge (overdosing on them and all that), and since you aren't allowed to do the diet until well and signed off, it sounds really strange.
I did have a client who had to have extra vit B owing to a blood disorder which meant she could absorb it properly, and had to get it cleared through Medical. And the doctor had to monitor throughout to make sure she wasn't getting too much.
Okay...so less ramble. Only your dr would be able to advise on this, or your consultant should contact Cambridge medical.