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Whether you’re naked and hungry on the savanna, driving in traffic or at the controls of your favorite video game, being slow to react can get you eaten, injured or splattered across the screen. While we intuitively know this, a new study offers evidence of how much speed of response still matters: In men and women from ages 20 to 59, slower-than-average reaction time turned out to be a pretty good predictor of premature death.

The new research, published last week in the journal PLOS ONE, was large, simple and revealing. Between 1988 and 1994, researchers gave 5,134 American adults younger than 60 a straightforward test of reaction time: The participants, all part of a large federal study of nutrition and health, were seated at a computer and told to push a button immediately upon seeing a 0 on the screen in front of them. There was no practice period; a participant’s average over 50 trials was computed, and he or she had just a few seconds between those 50 trials.

Researchers measured the range of reaction times across the group. They computed a “standard deviation,” a unit of measure that marks the extent to which an individual’s performance departs from the group’s average. They took note of the “variability” of each participant’s response time, or how widely reaction time fluctuated in the course of 50 tries.

Then they waited close to 15 years to see who in this relatively young group of Americans would die, and of what.

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Because participants had been recruited for an ongoing study of health and nutrition, researchers had a wealth of health-related information on them. They could use that data to adjust for risk factors such as age, gender and ethnicity.

In all, 378 participants died during a follow-up period that averaged 14.6 years.

When the researchers — all from the University of Edinburgh — went back to compare participants’ response times with their likelihood of being among the dead, they detected a clear pattern: For those with slow reaction times, each standard deviation that separated an individual’s performance from the group’s average increased his or her likelihood of dying by 25 percent.

Those who were slower than the group average by four standard deviations were twice as likely as those whose performance was average to have died over the 15-year follow-up period.

High variability in response time was also linked to a higher risk of death in the study. But those with high variability in response time also tended to be the same people whose response time was slower than average.

The authors noted that response time and variability were as powerful at predicting the likelihood of death as was another influential risk factor for death: smoking.

Response speed was much more likely to predict cardiovascular death than it was to predict death by cancer. This suggests that long before a stroke or heart attack fells its victim, the creeping progress of narrowing arteries, inefficient blood flow and weakening hearts might be evident as a slowing of response time, the study authors wrote.

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