They have investigated the claim by GlaxoSmithKline and have decided they can continue to use the claim in their marketing of lucozade.
Studies on Lucozade Energy have found that it enhanced concentration during a period of sustained mental demand and also significantly improved the accuracy and speed with which participants performed tasks requiring sustained attention or concentration.
This is from
Also, from www.new-nutrition.com...
formulated to enhance mental performance
The amount of caffeine and glucose in the drink is the reason lucozade gives energy to the brain.
Definitions for health and nutritcian claims in Europe are being debated in the European parliment, so this ruling may well alter in the future.
While I was searching for this, I came across this advert from 1951, which you may enjoy.