A study by the Institute for Scientific Information on Coffee may explain why you can't sleep at night after a cup of coffee in the late afternoon while it may not be a problem for others. The report, "Genetics, Metabolism and Individual Responses to Caffeine", looks to our genes for answers.
"We are all unique coffee drinkers. Our genetic make-up programs our reaction to caffeine, just as it programs our hair colour and eye colour," said the study's lead author, Dr. JW Langer.
The two genetic factors that determine one's caffeine intake are the liver's speed of metabolization and the sensitivity of the central nervous system to caffeine's stimulating impacts.
Langer and his team found there are three types of coffee drinkers:
1. HIGH SENSITIVITY TO CAFFEINE
People in this group most likely struggle to sleep after a cup of coffee in the afternoon because of their sensitive central nervous system and slow metabolism. It is recommended that they avoid caffeine outside of breakfast time.
2. REGULAR SENSITIVITY TO CAFFEINE
The most common group, this category of people has genes with moderate metabolism and typical binding in the central nervous system. They are likely able to consume two to five cups a day without any sleep issues, but are still recommended to stay away from caffeine once the sun goes down.
3. LOW SENSITIVITY TO CAFFEINE
These individuals have the fastest caffeine metabolization. They are capable of drinking coffee in the late afternoon without having their sleeping pattern disrupted. Still, professionals advise that they keep their coffee intake under the proposed limits of four cups per day.
"Most people will self-moderate their caffeine intake based on their personal experience of what they can tolerate. However, it's important that those with a low sensitivity to caffeine stay within the recommended daily caffeine intake of up to 400 mg caffeine," said Langer.