咖啡因是如何影响睡眠的？

蒋子慧

Whether its a cup of coffee， tea or an energy drink， many people look for a caffeine fix to kick-start their day. During waking hours， the stimulant（兴奋剂） can help people feel more alert and boost concentration. But how does caffeine affect sleep？

“A persons sleep pattern is unique to their body type， health and age，” said Lauri Leadley， the founder and president of the Valley Sleep Center in Arizona. “But everyone possesses a circadian rhythm（昼夜节律）， which means that theyre genetically determined to respond to the rising and setting of the sun. But caffeine can disrupt this natural sleep-wake cycle， impacting sleep.”

According to a 2022 review in the Journal of Sleep Research， adenosine（腺苷）levels are typically higher at night， meaning people feel sleepy by bedtime. Consuming caffeine inhibits（抑制）adenosine， which can make people too alert to drift off， Caffeine also interferes with sleep-inducing hormones（荷尔蒙）. “When we consume caffeine during the day， by nighttime it causes a reduction in the main metabolite （代谢物） of melatonin， the sleep-promoting hormone， which is one of the reasons sleep is interrupted，” said Dr. Peter Polos， asleep medicine specialist.

Once in the body， caffeine continues to exist for several hours， said Leadley， taking about 6 hours for one half of caffeines effects to be eliminated. A 2013 study in the Journal of Clinical Sleep Medicine divided people into three groups， with individuals drinking caffeine 6 hours， 3 hours or immediately before bedtime. Even those who stopped drinking caffeine 6 hours before bed had their sleep cut by a whole hour.

But caffeine doesnt just affect the length of sleep it also affects sleep quality， “Studies show that caffeine reduces slow-wave sleep， which is the stage of deep， restful sleep that leaves us feeling refreshed and alert in the morning，” Polos said. It is a stage of sleep that seems to play an important role in growth， memory， and immune function. Most adults spend around 10% to 20% of their sleep in slow-wave sleep.

However， how much a person responds to caffeine is affected by factors including age and genetics. One 2017 review in the journal Sleep Medicine Reviews suggests that people become more sensitive to the stimulant properties of caffeine as they get older， while differences between people of the same age could be related to genetic differences in the release of adenosine.

（材料来自livescience， 有删改）

1.Which of the following option is incorrect about caffeine according to the passage？

A. It helps people feel more alert and boost concentration.

B. The intake of caffeine leads to an increase in adenosine levels.

C. Caffeine can disrupt this natural sleep-wake cycle， impacting sleep.

D. It interferes with adenosine and some hormones.

2. Why does the author mention the 2013 studying para. 4？

A. To compare the research in para.3.

B. To back up Leadleys theory.

C. To pave the way for results.

D. To solve a problem.

3. What can we learn about slow-wave sleep？

A. It is essential for human health.

B. It is unaffected by caffeine consumption.

C. It occurs during the middle stages of the sleep cycle.

D. It accounts for the majority of adults total sleep time.

4. What is the journal Sleep Medicine Reviews suggests？

A. The older people get， the less sensitive they are to the stimulation of caffeine.

B. The older people get， the more sensitive they are to the stimulation of caffeine.

C. Caffeine has the same stimulating effect on people at any age.

D. The stimulating differences of caffeine among peers are the same.

1. B。解析：细节理解题。材料第三段第一句提到“当人们进入深度睡眠时，他们的腺苷水平会上升”。由此可知，并不是咖啡因的摄入导致了腺苷水平的上升，故选B。

2. B。解析：细节理解题。材料第四段第二句提到“《临床睡眠医学》杂志2013年的这项研究将人们分为3组，证明即使是那些在睡前6小时停止饮用咖啡的人，他们的睡眠也会减少整整1个小时”，与第四段第一句Leadley说，“咖啡因一旦进入人体内，就会持续存在几个小时，大约需要6个小时才能消除一半的咖啡因影响”相吻合。B选项与材料内容相符，故选B。

3. A。解析：细节理解题。材料倒数第二段第二句提到“研究表明，咖啡因会减少慢波睡眠，慢波睡眠是深度、宁静睡眠的阶段，让我们在早上感到神清气爽和警觉”，由此可知，慢波睡眠不仅对睡眠有好处，而且有利于身体健康，故选A。

4. B。解析：推理判断题。材料最后一段提到“《睡眠医学评论》杂志2017年的一篇综述表明，随着年龄的增长，人们对咖啡因的刺激特性变得更加敏感，而同龄人群之间的差异可能与腺苷释放的基因差异有关”，故选B。