Green tea, epigallocatechin gallate and the prevention of Alzheimer's disease: Clinical evidence

Given its increasing global prevalence, Alzheimer's disease (AD) has become a major public health challenge worldwide. The symptomatic treatments available for AD have shown no significant efficacy, and no disease-modifying interventions are capable of slowing the progression of the disorder. The potential of lifestyle-related factors, including diet, is increasingly recognized as an important consideration in the primary prevention of AD. Numerous mechanisms potentially underlying neuroprotective effects of bioactive components contained in tea, such as (–)-epigallocatechin-3-gallate, as well as their preventive efficacy against AD, have been elucidated in preclinical studies. However, in contrast to the abundance of mechanistic findings in animals, clinical results demonstrating efficacy in humans are scarce. While epidemiological studies have provided some evidence indicating that green tea consumption is associated with a reduced risk of age-related cognitive decline and AD, a causal relationship cannot be established on the basis of these observations. The clinical evidence regarding preventive or therapeutic effects of green tea and its bioactive components is unsatisfactory. A role of green tea in the prevention of AD cannot be recommended until well-designed, randomized, placebo-controlled clinical trials using standardized formulations confirm the purported beneficial effects of green tea.