It has long been accepted that the roots of depression and anxiety can begin in early childhood, but only recently has there been evidence that these roots can reach even into the womb. Dr. Ian Colman greatly expanded our knowledge of risk factors by publishing a new study in Biological Psychiatry that links depression and anxiety to birth-weight.
Dr. Colman began his study with some confidence that birth-weight had an impact on mental health. In an article back in March, we discussed a study of births in North Carolina that found a link between depression and low birth weight (LBW) in girls but not boys. Dr. Colman found the link in both sexes, a difference that should not just be attributed to the use of British rather than American children. Dr. Colman’s study was probably able to detect a correlation that the prior study missed because of the amount of subjects involved and the amount of time that these subjects were monitored. Three times as many babies (4627) were followed in Dr. Colman’s study, and they were followed far past adolescence. Follow-up evaluations were administered when the babies grew to 13, 15, 36, 43, and 53 years old.
Evaluations, based on the observations of parents, teachers, and, later in life, clinicians, allowed subjects to be divided up into six categories: absence of symptoms, repeated moderate symptoms, adult-onset moderate symptoms, adolescent symptoms with good adult outcome, adult-onset severe symptoms, and repeated severe symptoms over the life course. The heavier the baby, the less likely it was to suffer repeated severe symptoms. As with most good things though, weight was only healthy in moderation. After 10 pounds, the chance of mental illness starts to increase.
It is not known why LBW is a risk factor for mental illness. A common contention is that the same deficiency in the womb that impairs body growth also impairs neural development. Anything from a lack of essential nutrients to an excess of toxic substances could cause this dual retardation of growth. It is also possible that there are subtler genetic or neurochemical differences in mothers of small babies, or that the impairment of one type of growth causes the other instead of co-occurring. Dr. Colman tried to adjust for obvious social differences between mothers, but there are so many potentially confounding factors— parental depression, smoking, etc. — that many further studies are needed to explore the exact nature of the link between mental illness and birth-weight.
Even before we fully understand the link, we can start to take action on the information that we do know. Babies with LBW should be carefully monitored throughout their lives for signs of depression and anxiety. Of course not all scrawny babies will turn out to have problems, but parents should be more vigilant in picking up signs of emotional problems in these children. It is disturbing to think that half a pound at birth can affect the quality of life at 53 years old, but it is heartening to know that our expanding knowledge of this link enables us to attenuate it.
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