Babies older than three months who cry uncontrollably without reason are at greater risk of suffering from lower IQ, hyperactivity and discipline problems in childhood, new research has found.
Persistent crying for periods longer than two weeks after that age may suggest subtle neurological problems that are later responsible for developmental deficits, said federal government researchers.
Persistent and unexplained crying when babies are younger than three months - commonly known as colic - was not associated with cognitive problems later on.
"Children who had prolonged crying, but not those who had colic, had poorer outcomes on many of the tests of cognitive development," the researchers wrote in a paper published in the Archives of Disease in Childhood.
The study was based on 327 children in Norway and Sweden who were evaluated at 6 and 13 weeks and had their IQs measured when they were five years old. While the study was small, the researchers said the stark differences between the groups strengthened their confidence in the results.
The researchers found no obvious differences to explain the prolonged crying in babies older than three months. While maternal smoking has long been associated with colic, it was not associated with prolonged crying after babies were older than three months.