For some individuals, consuming a cup of coffee in the morning is an integral part of their day. Morning coffee may aid in alertness, improve concentration and signal the beginning of the day. Still, recent research is posing an important question on the duration of caffeine’s effects. Although ingested early in the day, caffeine may affect sleep at night in some individuals.
A comprehensive review was made of 32 prior studies, conducted by researchers from Wroclaw Medical University in Poland, that measured brain activity using an electroencephalography (EEG) while people were sleeping. The authors concluded that caffeine was related to for lighter, less restorative sleep, including decreases in slow-wave activity related to deep sleep.
What is mainly remarkable about the result is that it may not be perceived by the person involved. For example, an individual could go to bed at their normal time, stay in bed for a period of 7 to 8 hours and still have the change in sleep quality. Caffeine increases waking-like brain activity during sleep, which can mean a reduction in some of the essential slow-wave sleep for physical and mental restoration.
Caffeine inhibits the activity of adenosine receptors in the brain. Adenosine accumulates during the day, until it causes sleep pressure. When we interfere with the accumulation of sleep pressure, we tend to feel energetic. The issue with this is that this feeling of energy can last for many time.
The effect of coffee on sleep can vary among individuals. Factors like genetics metabolism habitual caffeine intake, age, and intake volume can all affect the extent of sensitivity. For one individual, a single small cup at breakfast may result in a negligible effect, for another it may affect sleep even after many hours.
Caffeine dose is also important. A randomized control study demonstrated no significant effects on sleep of a 100mg dose of caffeine taken 4 hours before sleep, while a 400mg dose delayed sleep onset and affected sleep architecture when taken 12 hours before sleep with the effect increasing as the administration time was closer to sleep.
Another study has issued a similar warning. A systematic review and meta-analysis of the sleep effects of caffeine concluded that caffeine reduced total sleep time by an average of 45 minutes, reduced sleep efficiency, and decreased the time spent in deep sleep stages. Using those results, the researchers estimated that a typical 250 mL mug of coffee with about 107 m g of caffeine in it should be consumed no less than 8.8 hours before going to sleep to prevent it from much decreasing total sleep time.
(3) The research but did not mean that everyone should suddenly dump their daily cuppa. In fact, other studies show that there are benefits to drinking coffee in the morning against throughout the whole day. For example, an extensive study on over 40,000 adult people indicated that subjects whose preferred time to have coffee was before midday had minimized estimated risks of death from cardiovascular diseases and all causes versus those who did not drink coffee; though the research did not conclude causal relationships.