A new meta-analysis finds genetic reasons why caffeine has different effects on different people, according to its authors, from Harvard School of Public Health and Brigham and Women's Hospital - both in Boston, MA.

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Coffee intake is "naturally modulated" by individuals in order to experience the optimal effects of the caffeine, argue the researchers.

Although scientists have previously believed there to be a genetic mechanism behind individual responses to caffeine, pinpointing the specific genetic variants responsible for differences in caffeine response has been difficult.

Back in 2006, Medical News Today reported on a study published in JAMA that examined how the different genetic profiles of coffee drinkers may influence whether drinking lots of coffee is good or bad for the individual's heart.

The researchers behind that study - from the University of Toronto, Canada - found that people carrying a version of a gene responsible for slow metabolism of caffeine had a 36% higher risk of heart attack if they drank up to three cups of coffee a day, compared with people carrying the same gene who only drank one cup a day.

However, people who had a version of the gene that was responsible for fast caffeine metabolism were found to have a lowered risk of heart attack if they drank up to three cups of coffee a day.

Genome-wide meta-analysis assesses more than 120,000 coffee drinkers

In the new study - produced as part of the Coffee and Caffeine Genetics Consortium and published in the journal Molecular Psychiatry - the researchers performed a genome-wide meta-analysis of more than 120,000 regular coffee drinkers. The participants in the study were Americans of European and African ancestry.

The researchers identified two gene variants - POR and ABCG2 - related to caffeine metabolism and two gene variants - near genes BDNF and SLC6A4 - that may influence the "rewarding" effect of caffeine. Also, two genes involved in glucose and lipid metabolism - GCKR and MLXIPL - were associated for the first time with the metabolic and neurological effects of caffeine.

Marilyn Cornelis, research associate in the Department of Nutrition at Harvard School of Public Health and lead author of the study, describes the results:

"Coffee and caffeine have been linked to beneficial and adverse health effects. Our findings may allow us to identify subgroups of people most likely to benefit from increasing or decreasing coffee consumption for optimal health.

The new candidate genes are not the ones we have focused on in the past, so this is an important step forward in coffee research."

The study suggests that coffee intake is "naturally modulated" by individuals in order to experience the optimal effects of the caffeine.

"Like previous genetic analyses of smoking and alcohol consumption, this research serves as an example of how genetics can influence some types of habitual behavior," said Daniel Chasman, associate professor at Brigham and Women's Hospital and the study's senior author.

Earlier this year, MNT reported on another study from the Harvard School of Public Health and Brigham and Women's Hospital examining the health benefits of increased coffee consumption.

The authors behind that study performed a systematic review of three large studies covering a 20-year period.

They found that participants who increased their daily coffee consumption by more than one cup a day over a 4-year period had an 11% lower risk of type diabetes over the following 4 years, compared with people who did not change their intake.