Slower reaction times and poorer memory are associated with a greater risk of dying in young and old people, a new study shows.
The finding in younger subjects is especially surprising, given that prior research linking higher mortality with poorer cognitive function in the elderly was attributed to degeneration of the brain due to aging.
"These results suggest that reaction time is not merely an indicator of age-related physiological deteriorations but rather an indicator of the brain's more basic information processing ability, suggesting that slower and more variable processing skills are a risk factor for mortality in themselves," said authors led by Beverly A. Shipley, Ph.D., of the University of Edinburgh in Scotland
In the study, published in the latest issue of the journal Psychosomatic Medicine, researchers followed 6,424 subjects age 18 to 94 from the 1984-1985 UK Health and Lifestyle Survey to assess their scores on cognitive tests and risk of death over 19 years.
Between July 1985 and May 2003, 1,366 of the participants had died. Of these, 52 were age 20 to 29 years, 351 were ages 40 to 59 years, and 963 were age 60 and older. Lower scores on simple reaction time (pressing a key after seeing a prompt), choice reaction time (pressing one of four keys after seeing a prompt), variability of reaction time and, to a lesser degree, memory performance were strongly associated with higher mortality rates in the youngest and the oldest group, but not the middle group.
The researchers factored in other lifestyle factors associated for risk of death such as smoking, heavy alcohol use and being overweight before making a final determination a the association between cognitive results and mortality risk.
The reasons for the association are unclear, but according to the authors, "The cognition-mortality relationship may be explained in part by the brain's efficiency of information processing and memory performance."
Other reasons for the results, the researchers say, may be that reaction time is linked with overall body deterioration, and in the youngest group, may be linked to brain functions associated with survival. For example, "higher cognitive ability may be linked to behaviors that are conducive to good health such as healthy eating, a low alcohol intake and avoidance of smoking," according to the authors.
Peter Muennig, M.D., of Columbia University, said the study is "of critical importance in public health. If cognition is a major factor in determining human life expectancy, then education interventions have the potential for great public health impact." He said, "So far, there is good evidence that years of schooling prolongs life expectancy. This will make a strong contribution to this argument."