Persistent tummy ache in some children may be linked to emotional problems in their families, a study suggests.
Stomach ache is common among children
Researchers found the mothers of children who repeatedly complained of symptoms were more likely to suffer with depression and anxiety.
Researchers say the findings suggest doctors treating children for recurrent abdominal pain need to consider psychological factors.
The study, by the University of Bristol, is published in Pediatrics.
It is based on the experiences of 10,200 families taking part in the Children of the 90s project.
Psychiatrist Dr Paul Ramchandani and his colleagues found that 55% of six year-olds had complained of pains in their stomach at some time in the past year.
Some 11.8% had stomach ache at least five times in the year.
Girls were more affected than boys.
The children who complained of persistent pain at age six were often the same children who had complained of tummy ache at age two.
When researchers examined these children's psychological assessments they found that they were more than three times as likely to have emotional problems.
Also, their mothers tended to have more symptoms of anxiety and depression.
Recurrent abdominal pain is among the most common complaints of childhood.
It is not usually associated with physical disease, although it is associated with complaints of other physical symptoms such as headache.
Dr Ramchandani said: "For many children the occasional stomach ache is all part of growing up and is usually a symptom of a childhood illness which can be treated normally.
"It is the recurrent stomach ache - which often seems to have no obvious cause - which we were investigating here."
"We need to consider carefully the possible role of parental distress and illness in some of these families.
"The fact that this seems to affect the same group of children across childhood - and may go on into adult life too - highlights how important it is to address these issues early in the child's life."
"The link we have shown between recurrent abdominal pain and emotional symptoms, in children and their parents, supports the view that doctors should be at least considering psychological factors in these cases."
Dr Alastair Forbes, medical director for the digestive disorders charity Core, said: "Well-informed paediatricians and gastroenterologists have always had this in their minds.
"However, the new data are helpful and add more substance to our previous impressions."
Dr Mike Cohen, a GP in Bristol and a member of the steering committee of the Primary Care Society of Gastroenterology, said previous research had suggested children with recurrent abdominal pain grow up to have higher levels of anxiety and depression.
He said: "We see many of these difficult cases regularly in our surgeries and it is vital that we GP's view these patients holistically and from all angles."