In a report titled "Vocabulary From Adolescence to Middle-Age" (PDF), two researchers at the UK's Institute of Education studied the the vocabulary test scores of 9,432 test subjects in their early forties. The results were then compared to the tests that the participants had taken as children and sorted based on each test subject's childhood reading habits.
Researchers Alice Sullivan and Matt Brown found that those who had read for pleasure at the age of 10 scored 67% on the vocab test when tested at the age of 42, but those who hadn't read for fun as kids scored an average of only 51%.
The study also showed that what people chose to read as adults mattered as much as how often they read. The greatest improvements in vocab scores between the ages 16 and 42 were made by test subjects who identified themselves as readers of 'highbrow' fiction. That group scored an average of 5 points higher on the test.
What's more, the study also noted that the newspapers read by a test subject could be having an effect on their test scores. The study found that those who read a tabloid regularly actually made slightly less progress than those who never read newspapers, while readers of better newspapers showed greater improvements in their test scores.
"The long-term influence of reading for pleasure on vocabulary that we have identified may well be because the frequent childhood readers continued to read throughout their twenties and thirties," say the researchers, Alice Sullivan and Matt Brown. "In other words, they developed 'good' reading habits in childhood and adolescence that they have subsequently benefited from."
And finally, the study found that reading was a popular pastime at age 42. Just over one in four people (26%) said they read books for pleasure every day, and a further 13 per cent said they did so several times a week.