SAN FRANCISCO -- She's a bright preschooler, independent, concerned about her friends and great with language. He's the same age, but not very smart, and he snatches toys from other kids and acts impulsively.
They're quite different now, but a new study suggests that both may be at risk for depression as young adults.
In particular, the study suggests intelligence is "a mixed blessing for some girls," said researcher Per Gjerde.
It probably doesn't raise the risk of depression by itself, he said. Rather, "in some of these smart preschool girls, there are certain vulnerabilities that we don't understand very well, and we are now trying to map."
The work has followed about 100 participants from preschool years through age 23 in an attempt to find early-childhood roots for adult depression. The findings suggest the pathway may be much more complex for girls than boys, said Gjerde, of the University of California at Santa Cruz.
He presented the work Friday at the annual meeting of the American Psychological Association.
Participants in Gjerde's study were tracked for personality, intelligence and depressive symptoms periodically from ages 4 to 23, through reports by nursery school teachers and by tests they took themselves. About two-thirds of the subjects were European-American, and about a quarter were black.
Analysis showed that preschool boys who would show chronic depressive symptoms at 23 tended to be impulsive and aggressive, and have trouble in getting along with peers. And while high intelligence was related to a greater risk of later depression in girls, boys showed just the opposite.
Gjerde found that about one-fifth of the girls followed a puzzling course during the study.
"They seem to start out very well," he said. "They seem intelligent, they seem to get along well with other people," and show concern for others.
The shift comes in early adolescence, he said, when they suddenly seem unable to handle stress and their relations with other people deteriorate.
Why? Maybe intelligence teams up with sensitivity to others to make them unusually aware of their problems and those of other people, he said. If they become overinvolved in the problems of others, it might drag down their mood, he said.
Carolyn Zahn-Waxler of the National Institute of Mental Health, who didn't participate in Gjerde's study, agreed that if a girl is extremely sensitive to others' needs and what other people think of her, it can set her up for depression later in life.
Zahn-Waxler, who studies children at risk for mood disorders, said she also doubted intelligence itself raises a girl's risk for later depression. Rather, she said, "it may increase the risk when you're already the type of girl who worries a lot about things, including relationships, and tends to be somewhat introspective and ruminative."