Coffee: key to cooked-meat vulnerability?

Heterocyclic amines (HCAs) are not carcinogenic until chemically altered in the liver by a pair of enzymes, each of which controls a separate stage of this two-step process (SN: 1/8/94, p.22). Depending on the genes inherited, a person may produce small, intermediate, or large amounts of the enzymes, notes Fred F. Kadlubar of the National Center for Toxicological Research in Jefferson, Ark. The more enzyme present, the faster the transformation. And individuals possessing genes to carry out both stages rapidly risk activating the most HCAs--the ultimate carcinogens that circulate through the body.

With Nicholas P. Lang of the Arkansas Cancer Research Center in Little Rock, Kadlubar found that the HCA-activating enzymes are the same ones that begin and end the metabolism of caffeine. To learn who carried the genes to complete both stages quickly, they asked 280 people to drink 9 ounces of coffee. Then they scouted for "rapid-rapid" individuals by monitoring their excretion of by-products from the first and last stages of caffeine breakdown. One-third of the people suffered from colon cancer--a malignancy linked to HCAs in animal and human dietary studies.

In the coffee test, "The really striking thing was that only 16 percent of the [cancer-free individuals] were rapid-rapid, while 35 percent of the cancer patients were," Kadlubar says.

Each volunteer also answered a dietary survey. Among its questions: When you have red meat, do you eat it well-done, medium or rare?

A preliminary analysis shows that, compared with cancer-free people, almost twice as many colon cancer patients -- 45 percent--preferred their meat well-done. This pilot study indicates that those with the genes to carry out both phases of HCA transformation rapidly--and who like their meat well-done--are six times as likely to develop colon cancer as slow-slow individuals who favor rare fare, Kadlubar says.

Such high-risk people over age 40 "should be strongly encouraged to have regular colonscopies"--to diagnose polyps that can be removed before they turn cancerous, Kadlubar says.

In the meantime, Kadlubar observes, their data show "a very rough relationship between the number of cups of coffee an individual consumes each day and whether they're a rapid-rapid metabolizer." He speculates that many heavy coffee drinkers refill their cup to compensate for their body's rapid breakdown of caffeine.