The birth of the blues
If all babies were born weighing at least 5.5 pounds, the prevalence of later adolescent depression among girls would drop by 18 percent, suggests a new study published in the March issue of Archives of General Psychiatry.
To reach this surprising finding, a team of researchers at Duke University School of Medicine examined more than 1,400 children between 9 and 16 years old, half of them girls. They found that about 8 percent of girls of normal birth weight developed depression during adolescence, compared with 38 percent of girls who weighed less than 5.5 pounds at birth. Adding two stressful episodes to the teens' lives, such as poverty or a traumatic event, causes depression to rise to about 15 percent among normal weight girls, but to skyrocket to 80 percent for low birth-weight girls.
Boys, however, showed no link between birth weight and later depression. "Why girls and not boys? We don't know," says lead author Elizabeth Jane Costello, a psychologist at Duke. But the difference might make sense, she says, if the depression link is tied to the effects of low birth weight, or even fetal development, on hormones. Risk of depression in girls is known to be influenced by a rise in estrogen and testosterone. A similar rise in testosterone in boys doesn't seem to have the same harmful effect.
Parents and pediatricians of low birth-weight babies, says Costello, should closely monitor the kids' mental health at puberty.