Researchers studying the effects of caffeine on the blood-brain barrier-a membrane(細胞膜)that prevents chemicals in the bloodstream from entering brain tissue-have found that the bitter alkaloid can protect the brain from the damaging effects of cholesterol. Previous studies have shown that cholesterol can make the barrier "leaky," and Alzheimer's researchers suggest that this condition may make the brain vulnerable to damage that can contribute to dementia(痴呆). The study found that rabbits fed a high-cholesterol diet and given the daily caffeine equivalent of one cup of coffee had more intact(無傷の)blood-brain barriers than their non caffeine-consuming counterparts.