A page on the Ribena website promoting the Ribena Plus range said vitamin A "helps keep your vision in tip-top condition" and is "important for ... immunity too" and vitamin C "helps immunity" and is an antioxidant.
A visitor to the website challenged whether the statements were authorised on the EU Register of Nutrition and Health Claims.
GlaxoSmithKline acknowledged that some claims had been reworded to keep the language understandable and "more consumer-friendly".
It believed the claim that vitamin A "helps keep your vision in tip-top condition" was consistent with the authorised version that it "contributes to the maintenance of normal vision".
The company said its claims about the effect of vitamin A and C on immunity were consistent with the authorised version that said each vitamin "contributes to the normal function of the immune system".
But the Advertising Standards Authority (ASA) said GSK's claim that vitamin A helps to keep vision in "tip-top condition" would be understood to mean "very best" or "optimum" vision rather than the "maintenance of normal vision".
The ASA said: "We considered the reworded claim therefore exaggerated the effects of the substance."
Regarding the vitamin A and C immunity claim, the ASA said: "We considered that removing 'normal' from the authorised claim had changed the meaning by implying vitamin A would optimise the immune system rather than contributing to its normal function."