PNAS:一天8杯水,真的科学吗?
2016/10/17
人们似乎很习惯听到这样的劝诫:一天喝8杯水。但是,很难真正做到。现在,一项最新研究揭示了做不到的原因:当我们不渴时,吞咽机制会阻止我们摄取太多的水。科学家们强调,我们应该根据身体需求合理补充水分。


水对于生命的意义,不言而喻。它对于生命的存在、生命的演化都必不可缺。成年人60%-70%的体重由水构成。但是我们每天需要喝多少水呢?

民间有说法是:一天八杯水(每杯约250ml)。同样,在国外也有每天8杯8盎司的水。事实上,这种“8*8”规则并不成立,目前并没有科学研究明确规定我们每天补充最佳的水量。

然而相悖于这些建议,澳大利亚莫纳什大学生物医学研究所的Michael Farrell团队最新的研究表明,我们应该仅仅只在口渴的时候喝水就可以。相关研究成果发表在《Proceedings of the National Academy of Sciences》期刊。

大脑特定区域负责吞咽机制,抵制摄水过量

Farrell研究团队招募了一批受试对象,要求他们分别在锻炼后、口渴、不渴3个时间段补充大量的水。在受试对象喝水的时候,研究人员利用功能性磁共振成像(fMRI)检测了他们的大脑活动,同时测量他们不同情境下吞咽水的困难指数。

结果显示,相比于锻炼后补充水分,不渴的时候喝水吞咽难度增加了3倍。而且,当受试对象努力吞咽水时,他们大脑前额叶皮层的某些区域明显活跃。这意味着,这些特定区域负责吞咽抑制机理。

Farrell 表示:“我们第一次发现,当身体不缺水,吞咽反射机制会抑制喝水的欲望和难度。”

口渴的时候喝水

研究人员团队强调,补充过多水分易导致低钠血症。这一研究预示着,我们应该听从身体的需求合理补充水分,并不需要刻意规定,口渴的时候喝水就可以。

备注:文章编译、整理自“'Only drink water when thirsty,' study suggests”。

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  • Overdrinking, swallowing inhibition, and regional brain responses prior to swallowing

    In humans, drinking replenishes fluid loss and satiates the sensation of thirst that accompanies dehydration. Typically, the volume of water drunk in response to thirst matches the deficit. Exactly how this accurate metering is achieved is unknown; recent evidence implicates swallowing inhibition as a potential factor. Using fMRI, this study investigated whether swallowing inhibition is present after more water has been drunk than is necessary to restore fluid balance within the body. This proposal was tested using ratings of swallowing effort and measuring regional brain responses as participants prepared to swallow small volumes of liquid while they were thirsty and after they had overdrunk. Effort ratings provided unequivocal support for swallowing inhibition, with a threefold increase in effort after overdrinking, whereas addition of 8% (wt/vol) sucrose to water had minimal effect on effort before or after overdrinking. Regional brain responses when participants prepared to swallow showed increases in the motor cortex, prefrontal cortices, posterior parietal cortex, striatum, and thalamus after overdrinking, relative to thirst. Ratings of swallowing effort were correlated with activity in the right prefrontal cortex and pontine regions in the brainstem; no brain regions showed correlated activity with pleasantness ratings. These findings are all consistent with the presence of swallowing inhibition after excess water has been drunk. We conclude that swallowing inhibition is an important mechanism in the overall regulation of fluid intake in humans.

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