在西非，人们长期以来都咀嚼可乐果作为兴奋剂，因为它们含有在茶、咖啡和巧克力中天然存在的咖啡因。
In West Africa, people have long chewed kola nuts as stimulants, because they contain caffeine that also occurs naturally in tea, coffee, and chocolate.
这一新的研究成果对下面这一理论表示支持，即咖啡因这种天然的刺激物会防碍一种被称为腺苷(adenosine)的激素发挥作用，从而使血管变得狭窄。腺苷的作用则是让血管保持宽敞。
Research has supported the idea that caffeine, a natural stimulant, Narrows blood vessels by blocking the effects of a hormone called adenosine, which normally keeps them widened.
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