Nov. 21, 2005 (Toronto) — Low birth weight and various developmental problems during childhood may predict chronic mental disorders in adulthood, according to a new study.

In a presentation at the Third International Congress on Developmental Origins of Health and Disease (DOHAD), Ian Coleman, PhD, described mental health findings from a large, long-term study that tracked people from birth to adulthood. He is from the Department of Psychology at Cambridge University in Cambridge, England.

The study used data from the 1946 British Birth Cohort, also known as the Medical Research Council National Survey of Health and Development. Subjects in the cohort underwent seven assessments related to development prior to the age of 11 years and were evaluated for everything from weight and height, to academic achievement, the presence of serious physical illness, and more.

Mental health assessments were conducted when the subjects were five and 15 years old via surveys given to their school teachers asking about behavior. Mental health was assessed again at age 36 years using the Present State Examination; at age 43 years using the Psychiatric Symptom Frequency Questionnaire, and most recently at age 53 years with the General Health Questionnaire.

Based on mental health findings, the 4,627 subjects were each assigned to one of six mental health groups: persistent wellness (n = 1,561); persistent difficulties (n = 1,373); adult onset difficulties (n = 1,032); adolescent disorder with good adult outcome (n = 346); adult onset disorders (n = 199), and chronic disorder (n = 113).

"The question is, what happens before age 13 that might predict which group people end up in?" Dr. Owen said during his presentation.

One of the first things that stood out was birth weight. The group that had the best overall mental health long-term, the persistently well group, tended to be heavier at birth. "The group that had the worst mental health in the long run are the smallest babies. Everybody else is in between," he said.

Subjects in the chronic mental health group were more likely than those in other groups to be slower at meeting developmental milestones. They sat up, stood, walked, and talked for the first time at a later time than subjects in the other groups (P < .05), Dr. Owen said.

They also tended to have a shorter height and lower body weight at ages six and 11 years, and did poorly on cognitive tests at ages eight and 11 years.

Even when other factors known to contribute to mental health were taken into account, such as major stressful life events and parental divorce, low birth weight was still associated with increased risk.

"We're not saying every low birth weight child is going to have mental disorders, it just means that there is a subtle difference between them. And smaller babies are at slightly higher risk of mental disorders later on," Dr. Owen told Medscape.

Generally, it was found that "an additional kilogram of birth weight was associated with a 17% reduction in the likelihood of a mental disorder later on," he said.

But low birth weight alone cannot be considered a reason for mental health disorders. The development of mental health disorders is not straightforward, and even heavier infants can develop them later in life. What the study provides are further markers to help predict who might be at increased risk, Dr. Owen concluded.

The study was funded by the UK Medical Research Council.

Third International DOHAD: Abstract O-019. Presented Nov. 14, 2005.

Reviewed by Ursula Snyder, PhD