There are actually other sad people who have discussed this ad on other forums!
See
http://teknoscape.com.au/forums/printthread.php?t=12205
Here is their best guess at the words...
I'm vitamin A
I'll help you see
I'll help you grow
Germs don't like me
Ohhhhh we're the vitamin B's ooohhh
So if you're feeling low, no energy
look for our famous group, ohhhh
called the vitamin Bs
(I'm Vitamin C?)
I fight germs and diseases
they never have a chance
when you take a lot of meeee
(this might be wrong)
Get out in the sunshine
and get vitamin D
good for your eyes, good for your bones
here's vitamin E
(Thankyou very much vitamin D)
I'm vitamin E and I'm good for your corpuscles
take a lot of me and I'll get into you muscles
Ther're in vegetables dairy foods, meat and fruit so ask your mum today
a, B, C, d, E, a, B....