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 A new analysis of tens of thousands of human genomes identified six
new genetic variants associated with habitual coffee drinking that
may help explain why individuals respond differently to coffee.
"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,” senior author Daniel Chasman,
associate professor at Brigham and Women's Hospital, said in a
statement.
The researchers combined data from 28 studies of more than 120,000
regular coffee drinkers. Using self-reported coffee consumption in
cups per day and gene mapping, they looked for versions of genes
that regular coffee drinkers had in common.
In addition to two genes that had already been linked to caffeine
metabolism, they discovered two more locations in the genome tied to
the way the body processes caffeine.
Another two variants they pinpointed may influence the rewarding
effects of caffeine in the brain.
Still another two new variants may be involved in sugar and fat
metabolism.
People with gene variants for increased caffeine metabolism may tend
to drink more coffee because their bodies process it more quickly,
the authors write in Molecular Psychiatry.
“Many of us might know this already but there are obviously
differences in how we respond to coffee,” said Dr. Marilyn Cornelis
of the Harvard School of Public Health in Boston, lead author of the
study. “Some can handle four cups, and others can only handle one.”
Pinpointing the exact genes involved has been difficult, Cornelis
told Reuters Health by phone.
Six of the eight gene variants correspond specifically to caffeine,
not to coffee, she said. That makes sense since coffee is the main
source of caffeine in the diet, she said.
Genes aren’t the only factors that go into coffee consumption,
though. Social and environmental influences are important too.
“You need to consider that these genes have very small effects,” she
said.
If an individual has all eight gene variants pointing to habitual
coffee consumption, that would still only explain an additional half
a cup to one cup of coffee per day, she said.
“The maximum effect we can identify is about one cup,” Cornelis
said.
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And although it’s relatively easy for people to recall how many cups
of coffee they usually have each day, the definition of a “cup” and
the caffeine content of different coffee drinks can vary, she noted.
In the future, knowing our genetic relationship with coffee could
lead to individualized guidance on how much we should be drinking
per day, Cornelis said.
But first we would need to know the healthiest amount of coffee to
drink.
“Some people may get agitated or have difficulty sleeping if they
consume too much caffeine and then reduce their intake to develop a
coffee drinking habit that balances pleasant and unpleasant effects
of caffeine,” said another of the study’s authors, Rob M. van Dam of
the National University of Singapore’s school of public health and
National University Health System in Singapore.
“This suggests that there may not be an optimal amount of caffeine
that can be recommended to everyone, but that people should monitor
their response to caffeine and cut down on their consumption if they
experience unpleasant effects,” said van Dam.
In some research, coffee has been linked to protection against
certain health problems, and in others it was tied to adverse
effects.
Drinking coffee has been associated with lower risk of Parkinson’s
disease, liver disease and type 2 diabetes, but its effects on
cancer development, heart health and birth outcomes are still
controversial, the authors write.
So a genetic profile that reveals how much coffee a person can
drink, or is likely to drink still doesn’t tell us how much they
ought to drink, they caution.
“If you were to tell people their genotype and tell them that they
can metabolize caffeine quicker, they could drink more,” Cornelis
said. “The question is, at this stage we don’t know what kind of
guidance we would give them.”
SOURCE: http://bit.ly/1oQWG4r Molecular Psychiatry, online October
7, 2014.
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