December 11 (HealthDay News) -- A too-fast heartbeat in early adulthood is a warning sign for increased risk of cardiovascular problems decades later on, a Japanese study suggests.

The study of 614 residents of a rural farming community in southwestern Japan found that a heart rate greater than 80 beats a minute during a first examination in 1979 predicted the development of obesity and diabetes, which contribute to heart problems.

The findings, from Kurume University School of Medicine, were published online Dec. 11 in the American Journal of Hypertension.

A fast heart rate is a signal from the sympathetic nervous system, a part of the autonomic nervous system, which is the body's automatic pilot that governs instinctive responses, explained Mercedes Carnethon, assistant professor of preventive medicine at Northwestern University's Feinberg School of Medicine. She found the same rapid heartbeat association in a group of Americans she studied.

"If someone has a consistently fast heart rate, it is because of increased input from the sympathetic part of the nervous system because the body is preparing to respond to stress," Carnethon said. "There is an increase in levels of blood glucose -- essentially because the body is storing energy to prepare for fight or flight, so that predisposes to diabetes."

Carnethon's study followed Chicago residents even longer than the Japanese researchers. "Over a 33-year follow-up, we showed that people with a higher heart rate were more likely to have Medicare claims for diabetes-related conditions," she said.

There's a possible clinical use for the findings, Carnethon said, since doctors routinely listen to the heart rate.

"It is a very simple measure, regularly taken in clinical practice, that could be potentially useful because it suggests where there might be a higher incidence of heart risk and mortality," she said. "It is a first stage to alert the clinician that there might be something worth investigating."

The similar findings in the two studies half a world apart are noteworthy, Carnethon said. "We are always happy to see findings replicated by different investigators in different settings," she said.

Meanwhile, researchers are reporting a different built-in mechanism that protects a lucky few individuals from heart disease -- a genetic mutation that seems to reduce blood levels of the fats called triglycerides.

The mutation was found in members of the Old Order Amish community in Pennsylvania, said the lead investigator, Toni I. Pollin, an assistant professor of medicine at the University of Maryland School of Medicine.

Pollin and her colleagues looked through the complete genetic complement of more than 800 members of the Amish community. "We looked at genes involved in the response to dietary fat," she said. "One region came up strong on chromosome 11. This genetic marker was not too far from a cluster of genes involved in lipid metabolism."

The researchers closed in on one gene, designated APOC-3, according to a report in the Dec. 12 issue of the journal Science. That gene makes a protein that inhibits the breakdown of triglycerides. About 5 percent of the Amish in the study had a mutated form of the gene that limited production of the protein, and so they had low blood lipid levels.

"It is an apparent cardioprotective mechanism," Pollin said. "It raises the hope that by decreasing production of APOC-3 it could potentially be therapeutic."

It's possible that a drug designed to target the gene could be used to reduce levels of blood fats and thus reduce coronary risk, Pollin said.

The mutation has not been found outside the Amish community, Pollin said. "We have looked at 200 healthy individuals and have not found it, she said.

SOURCES: Mercedes Carnethon, Ph.D., assistant professor of medicine, Northwestern University Feinberg School of Medicine, Chicago; Toni I. Pollin, Ph.D., assistant professor of medicine, University of Maryland School of Medicine, Baltimore; Dec. 12, 2008, Science; Dec. 11, 2008, American Journal of Hypertension, online