Are You A Slow Caffeine Metabolizer? It Could Be Disrupting Your Sleep

Many of us like to start the day with a strong cup of joe to keep us going through the morning, but it turns out that some people might find their sleep impacted that evening.

This is due to the varying speeds at which different people metabolize caffeine and the impacts it can have on how tired you feel when evening rolls around.

Caffeine is a central nervous system (CNS) stimulant that works by blocking the receptors our brain that receive neurotransmitters, making us tired. When these receptors are blocked, the tiredness-inducing neurotransmitters cannot make us drowsy, helping us feel more awake. Slowly, the body metabolizes the caffeine, clearing the receptors and allowing the neurotransmitters to enter once again.

"Broadly speaking, people can be fast or slow caffeine metabolizers, and also there is some evidence that people may be high or low sensitivity to the effects of caffeine," Glen Davison, a professor in sport and exercise sciences at the University of Kent in England, told Newsweek. "So it is fairly well recognized now, in the scientific community, that people respond differently to caffeine—some of this is innate (determined by our genetic makeup), and some of it may be lifestyle-related (determined by how used to caffeine we are)."

People who burn through their caffeine faster will therefore be able to feel tired at the end of the day, while those who process it slower will still have some of their adenosine receptors filled and be less able to get tired in the evening, hitting sleep quality.

Whether we are slow or fast caffeine metabolizers may depend on our genes, Neil Clarke, an assistant professor in sport and exercise science at England's Coventry University, told Newsweek.

"Two of the genes which are thought to have the largest impact are CYP1A2 and ADORA2A. Caffeine metabolism is mainly determined by the cytochrome enzyme P-450 1A2 (CYP1A2)," Clarke said.

"Fast metabolizers of caffeine who have the CYP1A2 AA genotype and slow metabolizers have the AC or CC genotypes. A "slow" caffeine metabolizer... clears caffeine from their system about four times slower than fast metabolizers. This will affect how long caffeine can have its positive (or, if you can't sleep, negative) effects for."

"The ADORA2A genotype has also been implicated in sleep quality and increases in sleep disturbance and individuals with the CC and TC genotypes appeared to confer greater sensitivity towards caffeine-induced sleep disturbance compared to the TT genotype."

However, there is still a lot of research to be done into how caffeine affects the body, and the exact mechanisms behind how it is metabolized.

"It's not quite as simple as some people being fast caffeine metabolizers and others slow, almost nothing in human biology is simple, but some people are definitely more sensitive to caffeine than others," Thomas Merritt, a professor of chemistry and biochemistry at Laurentian University in Canada, told Newsweek. "Caffeine sensitivity also means different things to different people, but sleep patterns are often something that people are concerned about."

Caffeine is also linked to a number of other effects in the body, including weight loss and mental health.

"Caffeine in moderate doses acts within the brain to decrease fatigue, increase alertness, and decrease reaction time. Caffeine also may decrease appetite and slightly reduce weight gain. In moderate doses, caffeine has been associated with decreased risk of depression and suicide in some studies," Clarke said.

"Thinking about how a lot of people get their caffeine, coffee, coffee may contribute to the prevention of inflammatory and oxidative stress-related diseases, such as obesity, metabolic syndrome and type 2 diabetes; second, coffee consumption seems to be associated with a lower incidence of several types of cancer and with a reduction in the risk of all-cause mortality.

"Similarly, a recent review ... highlighted that decaffeinated coffee still contains polyphenols which have anti-inflammatory and antioxidant properties. Furthermore, some non-caffeine minor components, such as protocatechuic acid, have anti-bacterial and antifungal activities and a new role in glucose metabolism."

Do you have a tip on a science story that Newsweek should be covering? Do you have a question about caffeine? Let us know via science@newsweek.com.