Following an application from Comvita New Zealand Limited, submitted pursuant to Article 13(5) of Regulation (EC) No 1924/2006 via the Competent Authority of the United Kingdom, the Panel on Dietetic Products, Nutrition and Allergies (NDA) was asked to deliver an opinion on the scientific substantiation of a health claim related to olive (Olea europaea L.) leaf water extract and increase in glucose tolerance. The food that is the subject of the health claim, olive leaf water extract standardised by its content of oleuropein, is sufficiently characterised. The claimed effect, an increase in glucose tolerance, is a beneficial physiological effect as long as serum insulin concentrations are not disproportionately increased. One human intervention study showed an increase in glucose tolerance without disproportionate increase in insulin concentrations after daily consumption of the olive leaf water extract for 12 weeks under the conditions of use proposed by the applicant. However, the results have not been replicated in other studies, and no evidence has been provided in relation to the mechanism by which the olive leaf water extract could exert the claimed effect. The scientific evidence is insufficient to establish a cause and effect relationship between the consumption of olive leaf water extract and an increase in glucose tolerance.