Jobs with high intellectual demands are protective against dementia in old age, and this benefit is strongest in persons with a lower intelligence. It seems that this is one of the rare cases where he that has plenty of goods shall not have more. The magic word is "cognitive reserve", and it once more has been found to explain facts in a study on job demands, intelligence, and cognitive performance of men in late life.
More than a thousand U. S. men, IQ tested as young soldiers, have later been contacted as World War II veterans in old age. In a special telephone interview, their cognitive status and their job history have been assessed. Every job has been analyzed for intellectual demand, for level of human interaction and communication, for physical activity and for visual attention. It came out that high intellectual job demands and intense human communication are both independently linked to a higher mental performance in old age. In contrast, a physically demanding job is linked to a lower performance. And very interestingly, the greatest benefits of a demanding job have been found in those with the lowest IQ results in young age.
This result strongly supports the concept of cognitive reserve. Those with high intellectual abilities in young age already have plenty of reserve, and a demanding job will not add very much. But those who start at a lower intellectual level have the chance to build up a substantial amount by using their brains.
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