Whether coffee makes a person anxious or helps boost their memory may come down to their DNA, according to research that suggests further studies on caffeine should be customized to a person's genetic profile.

A study reported Tuesday in the journal Molecular Psychiatry found six genetic variants associated with coffee drinking. The variants help explain why the same amount of coffee can have different effects in different people, said Marilyn Cornelis, the report's lead author.

"If we can understand some of the individual differences that underlie differences in response or overall intake, it could have important public health implications," said Cornelis, a research associate in the Department of Nutrition at Harvard School of Public Health in Boston.

Caffeine, the world's most widely used drug, has been linked to improvements in memory and protection against the destruction of brain cells. It can also lead to nervousness, anxiety, restlessness and gastrointestinal upset.

One of the next steps for scientists is to use the genetic variations found in the latest study to better understand the health outcomes on an individual basis from coffee and caffeine consumption, Cornelis said in a telephone interview.

The researchers analyzed more than 120,000 coffee drinkers of European and African-American ancestry. They identified two genetic variants involved in caffeine metabolism, two that potentially play a role in the rewarding effects of caffeine and two others involved in the interaction of fats and sugars in the bloodstream.

"They're regulating through modulating the amount of caffeine in our blood," Cornelis said. "If it's low, we'll tend to reach for another cup. If it's too high, we'll hold back. Other genes relate to the stimulating effect. If someone is feeling anxious, they will cut back.'"

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