TORONTO — Long known to be beneficial in heart disease, diabetes and some cancers, now a new study finds that a specific green tea extract may delay or prevent Alzheimer’s disease and dementia. A. Holliday & Company’s “Teawell 50,” is a 50 percent pure extraction of EGCG (epigallocatechin gallate) — a flavonoid which is the most potent of four major catechins found in green tea.