People in lower classes are not at increased risk of schizophrenia
Though they do not have an increased risk of the condition, the delay in diagnosis means they are likely to do less well.
Researchers from University College Dublin looked at the records for 352 patients referred to psychiatric services.
They found those in the lowest social class at birth were on average 33 when they sought treatment, eight years older than those in the highest social class.
First age of contact with the psychiatric service was defined as any inpatient or outpatient contact with a health service professional.
Cases were limited to those who were later admitted to hospital with schizophrenia.
Using birth registration details, researchers made a note of the father's occupation, and identified them as members of classes I (highest) to V (lowest).
As a comparison, the paternal occupation of the next baby of the same sex to be born in the district was logged.
Class movement
It had previously been thought that schizophrenia was more common amongst those from lower classes.
But the researchers say this may be due to people with schizophrenia moving into, or not moving out of, lower classes.
Writing in the British Medical Journal, the team led by researcher Fiona Mulvany said the difference in age at presentation for treatment was probably due to the recognised factor that people in lower classes are often less likely to seek help.
They suggest also that they may find it more difficult to access services, or that people from higher social classes know more about schizophrenia or spot it earlier.
"This delay may, at least partially, explain why people from lower social class have a less favourable outcome."
"Efforts to reduce the duration of untreated psychosis through earlier detection should be particularly focused on people in lower social classes."
Fiona Mulvany, a researcher in the department of psychiatry at the Cluin Mhuire Family Centre in Dublin when the research was carried out, told BBC News Online: "There doesn't seem to be anything to suggest that you would have a different age of onset in different social classes.
"Symptoms appear at the same time, but are detected later.
"Health services need to look to earlier detection and that would diminish the impact of the condition."
'Meaningful life'
Gary Hogman, head of policy and campaigns for the National Schizophrenia Fellowship, said: "This research highlights the urgent need to put in place the government's promised strategy to promote early intervention.
"We already know that there is an average delay of two years between a young person showing signs of schizophrenia and appropriate care and treatment being offered.
"This new research shows how those delays fall disproportionately on poorer communities. Any delay threatens an individual's chances of recovering a fulfilling and meaningful life."