Espresso, latte, or cappuccino. Most of us can’t move on with our day unless we have our regular cup. Now new, large-scale research has identified six genetic variants associated with habitual coffee drinking. The research led by Harvard School of Public Health and Brigham and Women's Hospital, identifies why coffee has different effects on different people and proposes to use this genetic research to explore links between coffee and health.

"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," said Marilyn Cornelis, research associate in the Department of Nutrition at Harvard School of Public Health and lead author of the study, in a statement.

The study appears in the online journal Molecular Psychiatry, on October 7.

People are known to respond differently to caffeine. While some can drink up to 6 cups of coffee a day and sleep like babies at night, others can lose sleep with only as much as a sip. Other side effects like headaches, nervousness, dehydration, and rise in blood pressure are also known side effects of coffee.

Whether you like to drink it or not, caffeine when consumed changes the way the brain and body and works. Caffeine is a central nervous system stimulant, and when consumed it enters the blood stream and remains there for a few hours, stimulating the brain and other nerves of the body. But people experience unhealthy side effects even long after the caffeine is no longer present in the blood.

This, according to scientists, is due to genetics that determines our individual responses to coffee. The current study took up the challenge of identifying the exact genetic variants that cause our reactions to caffeine. For this, the researchers, part of the Coffee and Caffeine Genetics Consortium, conducted a genome-wide meta-analysis of more than 120,000 regular coffee drinkers of European and African American ancestry.

They identified two variants that mapped to genes involved in caffeine metabolism, POR and ABCG2 (two others, AHR and CYP1A2 had been identified previously).

In addition, two variants were also found near genes BDNF and SLC6A4 that potentially influence the rewarding effects of caffeine. Two other variants found near genes that aid in glucose and lipid metabolism GCKR and MLXIPL, had never previously been associated with metabolism or neurological effects of coffee.

The research suggests that people adjust their coffee intake based on what best suits them in terms of metabolic and neurological satisfaction. And the strongest genetic factors linked to increased coffee intake are probably connected to caffeine metabolism.

This is a path-breaking research as it explores candidate genes that have not been implicated before, say the authors.

"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 senior author Daniel Chasman.

Source: Cornelis M, Chasman D, Byrne E,, Genome-wide meta-analysis identifies six novel loci associated with habitual coffee consumption, Molecular Psychiatry, 2014.