CHICAGO (AP) - Researchers say they have shown for the first time that treating a mother's depression can help prevent depression and anxiety disorders in her child, a provocative finding with potentially big public health implications.

The study was small, but the researchers and other experts called it convincing and said it illustrated how important a parent's well-being is to a child.

Depression runs in families and has a strong genetic component, but environmental factors can trigger it. The study results indicate that for children of depressed mothers, that trigger is sometimes their mothers' illness acting up, said lead author Myrna Weissman, a researcher at Columbia University and New York Psychiatric Institute.

Effective treatment for mothers could mean their children might avoid the need for prescription antidepressants, the researchers said.

In the study, those children whose mothers' depression disappeared during three months of treatment were much less likely to be diagnosed with depression, anxiety or behaviour problems than those whose mothers did not improve.

The study appears in the Journal of the American Medical Association and involved 114 depressed women assessed after three months of treatment. Of the 114 children participants, aged 11 to 12 on average, 68 had no psychiatric disorder when their mothers began treatment.

Among children with psychiatric problems, the remission rate was 33 per cent after three months for those whose mothers recovered, versus 12 per cent among those whose mothers did not.

Among children without psychiatric problems at the outset, all whose mothers recovered also remained healthy, whereas 17 per cent of those whose mothers remained depressed were diagnosed with psychiatric problems by the study's end.

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