In a new report for the Institute for Scientific Information on Coffee, research suggested most coffee drinkers can be categorized into three main types. And our genes can actually help explain why. The report titled "Genetics, Metabolism and Individual Responses to Caffeine" was published online June 6. "It's common for people to ask their doctor questions such as why they are kept awake by one cup of coffee, while their partner easily falls asleep after five cups," stated lead author Dr. J.W. Langer. "The answer is that we are all unique coffee drinkers. Our genetic make-up programs our reaction to caffeine, just as it programs our hair color and eye color." Two main genetic factors determine how a person responds to caffeine intake. First, whether their liver can metabolize caffeine rapidly or slowly. Secondly, their response depends on a genetic variation which increases the sensitivity of the central nervous system to the stimulating effects of caffeine. He proposed three main categories based on overall levels of caffeine sensitivity: 1. High sensitivity to caffeine This type of coffee drinker has a highly sensitive nervous system and slow metabolism in the liver. Stimulation can be triggered by even small doses of caffeine. Some people who fall into this category might even avoid coffee intake during the evening as it could potentially cause sleep disturbances. 2. Regular sensitivity to caffeine Individuals in this category have struck a balance between caffeine inactivation in the liver and binding in the central nervous system. In other words, they may be able to consume two to five cups of coffee per day without adverse reactions or sleep problems. Caffeine is normally not recommended in the evening, but individual differences prevail, as seen in most people. 3. Low sensitivity to caffeine This type of coffee drinker is the fastest metabolizer of caffeine among the three groups. Intake may be on the higher side and drinking coffee during the latter half of the day does not cause any sleep disturbances. Health professionals noted these people were still advised to stay under the proposed limits and not go over 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," Langer explained. A typical cup of coffee contains roughly 75 to 100 mg of caffeine. According to the report, other factors affecting caffeine metabolism are dietary patterns, alcohol intake, smoking status, liver diseases, pregnancy and the use of oral contraceptives. For future research, it was suggested populations could be categorized further by gene types to investigate the impact on various physiological functions during caffeine consumption. Source
