For many of us, it is the rocket fuel that gets us going first thing in the morning.
对我们许多人来说，早起第一件事喝杯咖啡，这就像是火箭燃料，能让我们清醒振作。
But one expert has argued that to get the maximum effect of caffeine, it's better to hold on a few hours - because coffee is most effective if consumed between 9.30am and 11.30am.
但是有专家认为，要想获得咖啡因的最佳效果还得再等上些许时间。因为在上午9：30-11：30这个时间段喝咖啡才是最有效的。
Steven Miller, a neuroscientist from the Uniformed Services University of the Health Sciences in Maryland, says it is best to drink coffee when the body’s levels of the hormone cortisol are low because caffeine interacts with the hormone.
马里兰州健康科学统一服务大学的神经学家史蒂芬·米勒认为，最好在身体中的荷尔蒙皮质醇水平偏低时喝咖啡，因为这时咖啡因和荷尔蒙相互作用。
He explained that people who drink coffee when their cortisol levels are high – namely, between 8am and 9am – develop a tolerance to caffeine, meaning it becomes less effective.
他解释道，上午8-9点时人们的皮质醇水平较高，此时喝咖啡，身体对咖啡因有耐受性，并不是很有效。
Cortisol controls the body clock and causes people to feel wide awake, The Telegraph reports. The body’s levels of the hormone are usually high just after a person wakes up but start to fall about an hour afterwards.
据《每日电讯报》报道，皮质醇控制人体生物钟，让人们感觉很清醒。人体内的激素水平在刚刚睡醒后通常较高，但大约一小时后开始下降。
Mr Miller argues that it is during this drop in cortisol levels that people get the most benefit from the caffeine in coffee – it gives them a boost as it encourages cortisol production when their cortisol levels start to drop and they do not become resistant to its benefits.
米勒先生认为，正是因为这种皮质醇水平下降，咖啡所含的咖啡因能够发挥最佳效果——因可以振奋精神，在皮质醇激素下降时刺激皮质醇产生，而且人体对咖啡因的吸收不会受到皮质醇的抵制。
He explained that cortisol levels also peak at lunchtime and between 5.30pm and 6.30pm, meaning that these would also not be good times to drink coffee.
他解释道，皮质醇水平在中午以及下午5：30-6：30之间达到峰值，这也就意味着这两个时间段也不是喝咖啡的最佳时间。
Writing on his blog he said: ‘If we are drinking caffeine at a time when your cortisol concentration in the blood is at its peak, you probably should not be drinking it.
他在博客中写道：“如果我们在血液中的皮质醇浓度达到高峰时摄取咖啡因，那么可能不应该在这个时候喝咖啡了。
‘This is because cortisol production is strongly related to your level of alertness and cortisol peaks for your 24 hour rhythm between 8 and 9am on average.
“这是因为皮质醇激素的生产与人的警醒度紧密相关，在一天24小时的生物钟里，早上8-9点皮质醇达到顶峰。”
He added that people who drink a coffee first thing in the morning, when their cortisol levels are naturally high, will soon find themselves needing to make their coffee stronger and stronger to get the desired effect.
他补充道，对于那些早上起床第一件事就是喝咖啡的人来说，由于那个时段皮质醇水平本身就高，他们很快就会发现，自己需要喝更浓的咖啡来达到所需的效果。
However, he did accept that cortisol levels at different times of day vary from person to person meaning that the best time of day to drink a coffee also differs between people.
不过，他确实也同意，在一天的不同时段人们的皮质醇水平互不相同。因此每天喝咖啡的最佳时间也因人而异。
For example, people who get up very early may find their cortisol levels drop earlier than those of people who get up late.
例如，早起的人可能会发现，与那些起得晚的人相比，他们的皮质醇水平下降的更早。
He says it helps turn energy into sugar to be utilised by cells in the body and that it also plays a role in controlling the body clock.
他说，这有助于利用体内细胞把能量转化成糖，并且对控制人体生物钟也起作用。