In previous studies, reading ability has been associated with improved health, education, socioeconomic status and creativity. The ability to read well can directly improve some of these factors. An example is that by being able to extract information from texts, individuals are better able to gain educational qualifications.
Early reading ability was not just associated with improved vocabulary and general knowledge, but also with improved nonverbal intelligence.
But some researchers have suggested that the act of reading has "a causal effect on more general cognitive abilities" that are associated with better life outcomes.
In short: reading itself may boost intelligence.
Other studies, however, suggest that there may instead be a shared genetic basis for reading and cognition. It is also possible that keen reading in children may reflect knowledge-seeking behavior rather than necessarily reading skill in itself, which could confound results.
To investigate the issue further, researchers from the University of Edinburgh and King's College London, both in the UK, compared the results of reading and intelligence tests from nearly 2,000 pairs of identical twins who were part of the Twins Early Development Study.
The tests were taken by the twins at the ages of 7, 9, 10, 12 and 16.
Twins were used because they are genetically identical - and in this study, the twin participants were also brought up in the same family environments - which allowed the researchers to isolate any differences that might be due to experiences not shared by the twins. Examples of this kind of non-shared experience might include having a particularly inspiring teacher or a friend who encourages reading.
The researchers found that twins with better early reading ability than their identical sibling would not only remain better at reading as they grew older, but would also score higher than their twin on general intelligence tests.
What is more, early reading ability was not just associated with improved vocabulary and general knowledge, but also with improved nonverbal intelligence.
"It's not too surprising that being better at reading might improve your vocabulary," lead author Stuart Ritchie told Medical News Today, "but it is more surprising that there were effects on nonverbal intelligence."
"It's possible that reading helps train children to use abstract thinking, as they have to imagine other people, places, and things while reading. This would be helpful in more general problem-solving tasks, such as those on IQ tests. Also, being better at reading might involve more practice of sitting down and concentrating on a task, which again would be useful for intelligence test performance."
As well as reading, Ritchie and colleagues suggest that other school activities such as learning mathematics, practicing self-control, or physical activity may also contribute to cognitive development, and they suggest that this should be a focus of future research.
The team also thinks that further studies should investigate the precise age at which reading begins to have an effect on cognitive development. In the new study, this age was 7, but as that was the earliest age group studied, the researchers suggest it is possible that this association could be found in even earlier readers.
'General intelligence' versus 'multiple intelligences'
For the study, Ritchie and his team set the children standard IQ tests to grade their "general intelligence," which involved vocabulary and general knowledge tests for verbal IQ, and pattern-completion reasoning puzzles for nonverbal IQ.
MNT asked Ritchie if other types of intelligence, such as the "multiple intelligences" categories of logical-mathematical, musical, spatial, bodily-kinesthetic and interpersonal intelligence were also cross-referenced against reading ability.
"Emotional intelligence, and even more so 'multiple intelligences,' are controversial constructs," he replied, explaining that many psychological scientists do not recognize them as "intelligences."
"They are not reliably separable - many of them can be subsumed under general intelligence, which is what we measured in this study. We would not have expected to find effects on very specific skills, such as musical ability."
Ritchie adds that general intelligence "has been shown in hundreds of studies across the past century to relate strongly to educational success, occupational success, and even health," pointing out that people who score higher on intelligence tests tend to live longer.
"So anything that genuinely boosts intelligence would be very important and useful. Another major finding in the psychological literature has been that all mental abilities tend to correlate positively together, and to some extent they all correlate with academic ability."
Earlier this month, Medical News Today reported on another UK-based study that found the same genes influence children's reading and math abilities.