Scientists reached the conclusion after assessing people's genetic risk factors and found the link exists even if they do not develop the condition.
The study shows genes associated with schizophrenia influence people in other important ways besides causing the illness itself, it was claimed.
Experts hope the findings will lead to new research into how different genes for schizophrenia affect brain function over time.
Schizophrenia, a severe mental disorder characterised by delusions and hallucinations, is partly caused by genetic factors and affects around 1% of the population.
Researchers at Edinburgh University used genetic analysis techniques to reach their findings.
They compared the IQ scores of more than 1000 people from Edinburgh who were tested for general cognitive functions in 1947, when the subjects were 11, and again when they were around 70 years old.
Scientists were able to examine people's genes and calculate each subject's genetic likelihood of developing schizophrenia, even though none of the group had ever developed the illness.
While there was no discernible difference at age 11, the study found people with a greater genetic risk of schizophrenia had slightly lower IQs at age 70.