Researchers from Scotland have found around one-quarter of changes in intelligence observed from childhood to old age may be due to our genes. Although the researchers accept the finding is not statistically significant, it is the first to estimate the contribution of genetic variations to cognitive ageing.
'Until now, we have not had an estimate of how much genetic differences affect how intelligence changes across a lifetime', said lead author Professor Ian Deary of the University of Edinburgh's Centre for Cognitive Ageing and Cognitive Epidemiology. 'Genetic factors seem to contribute much to the stability of intelligence differences across the majority of the human lifespan'.
The study, which was published in Nature, followed almost 2,000 people from Aberdeen and the Lothian area, for over 50 years. The participants were asked to complete intelligence tests when they were 11 years old, and again when they were between 65 and 79 years old. Combining the results from these tests with DNA samples taken from the participants in their old age, the scientists conducted a genome-wide association study covering over half a million genetic markers to determine how changes in intelligence over a lifetime could be associated with genetic variation.
The results indicated that 24 percent of the differences in intelligence between childhood at the age of 11 and old age were due to genetic variations, including a variation in the APOE gene that is associated with late-onset Alzheimer's disease. The findings suggested that both genetics and the environment could contribute to an association between intelligence measured in childhood and in later life, explained the researchers.
'The results partly explain why some people's brains age better than others. We are careful to suggest that our estimates do not have conventional statistical significance, but they are nevertheless useful because such estimates have been unavailable to date', said Professor Deary.
Further studies are needed to verify the researchers' interpretation of the results. As highlighted by NHS Choices, the cohort was too small to produce statistically significant findings and the study did not look at specific lifestyle or genetic factors that may account for changes in intelligence over a lifetime.
However, the study is valuable in capturing over half a century of information on cognitive stability and change. The estimates of the genetic and environmental contributions to changes in intelligence across most of the human lifespan could now be used to guide future research.
'It is incredibly positive as it suggests that we can have a real influence on how our brain ages through our lifestyle and other external factors', Professor James Goodwin of Age UK told the Daily Mail. 'The key now is to establish which lifestyle and environmental factors are most important so that we are able to do all we can to maximise our chances of ageing well'.