At the same time, other studies have identified a single nugget of our DNA that seems to determine whether we process caffeine quickly or slowly. That, in turn, appears to have a large effect on whether coffee is good for your health.

For those who process caffeine slowly, this line of research indicates, drinking coffee raises the risks of heart attacks and high blood pressure. For those who process it quickly, drinking coffee seems to be safe - it may even protect against a heart attack or high blood pressure.

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While researchers caution that more work needs to be done, they suggest that giving the public a general guideline regarding coffee doesn’t make sense. People are too different.

Here are some of the highlights in this line of research.

For the key studies in favor of coffee, try this.

“The interindividual differences in the 3-demethylation of caffeine alias CYP1A2 is determined by both genetic and environmental factors.”

Pharmacogenetics, August 2002.

http://www.ncbi.nlm.nih.gov/pubmed/12172216

Finding: Forty-nine identical twins and 34 fraternal twins were given 200 milligrams of caffeine; six hours later, a urine sample was taken. Those sample were then analyzed to see how quickly each person had broken down, or metabolized, the caffeine. In identical twins, the rates of metabolism were about twice as correlated as they were in fraternal twins. The scientists concluded that genetics largely determines the rate at which a person processes caffeine.

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“CYP1A2 phenotype and genotype in a population from the Carboniferous Region of Coahuila, Mexico.”

Toxicology Letters, April 2005

http://www.ncbi.nlm.nih.gov/pubmed/15763632

Finding: Scientists in Mexico gave 46 volunteers a cup of instant coffee containing 140 milligrams of caffeine. Eight hours later, urine samples were collected. Those subjects who had one variant of the CYP1A2 gene processed caffeine more than twice as quickly as those who had the other, researchers found. Other similar efforts in China and Germany found a link between the gene and caffeine metabolism, predominantly in smokers.

“Coffee, CYP1A2 Genotype, and Risk of Myocardial Infarction”

JAMA, March 2006

http://www.ncbi.nlm.nih.gov/pubmed/16522833

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Finding: Researchers compared about 2,000 people in Costa Rica who had a heart attack with 2,000 others who had not, examining both how much coffee they drank, as well as their DNA. In those subjects with the genetic marker indicating slow caffeine metabolism, the chance of heart attack appeared to rise with each cup of coffee. By contrast, those subjects with the genetic marker for rapid caffeine metabolism had a lower chance of heart attack with each cup.

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The authors concluded: “Intake of coffee was associated with an increased risk of nonfatal [heart attack] only among individuals with slow caffeine metabolism, suggesting that caffeine plays a role in this association.”

“CYP1A2 genotype modifies the association between coffee intake and the risk of hypertension”

Journal of Hypertension, August 2009.

http://www.ncbi.nlm.nih.gov/pubmed/19451835

Finding: Researchers looked at the genetics, blood pressure and coffee habits of 553 young Italian over more than eight years. As with heart attacks (see above), the effects of coffee diverged depending on a person’s genetics.

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For those with the gene for slow caffeine metabolism, the risks of high blood pressure rose dramatically with coffee intake. For those with the gene for rapid caffeine metabolism, the risk of high blood pressure dropped with coffee intake.