Cambridge study links birth weight and long-term mental health

The authors hope that their data will ultimately help identify the underlying mechanisms responsible for the different courses that mental health can take over an individual's life.

Led by Peter Jones, Professor of Psychiatry at the University of Cambridge and Dr Tim Croudace, Senior Lecturer in Psychometric Epidemiology, the work formed the basis of a Cambridge PhD awarded earlier this year to Dr Ian Colman, now at the University of Alberta. Their research is published in the December edition of Biological Psychiatry.

Dr Colman said, "We found that even people who had just mild or moderate symptoms of depression or anxiety over their life course were smaller babies than those who had better mental health. It suggests a dose-response relationship. As birth weight progressively decreases, it's more likely that an individual will suffer from depression and anxiety later in life."

Their study analyses data on symptoms of anxiety and depression over a 40 year period for more than 4,600 people born in Britain in 1946. A nationally representative sample was used and their symptoms were measured at ages 13, 15, 36, 43 and 53.

Professor Jones said "The key to the study lay in the application of new statistical approaches to understanding patterns of stability and change in mental health over such a long period of time. We were able to separate people into six distinct groups with a stable risk of anxiety and depression over half a lifetime, not just on whether they happened to be depressed or anxious at a particular time."

Their results will feed further into the 'nature vs. nurture' debate. They support the theory that conditions in the womb have an effect on our future development, in particular, a model of 'fetal programming' for depression and anxiety.

This posits that conditions in the womb result in permanent changes to the developing brain that programme later responses to stress and other environmental events, acting in concert with genetic characteristics. This programming may be reflected in birth weight, and appears important in many areas of later health, not just mental health.

The researchers emphasize that not all small babies will experience poor mental health in the future. Dr Colman explained, "Being born small isn't necessarily a problem. It is a problem if you were born small because of adverse conditions in the womb."

"If this [programming] theory is correct, you would find that when stressful events occur, the people who were smaller babies would be more likely to become depressed or anxious; this is an important idea to test in our future research", said Professor Jones and Dr Colman, adding that better maternal care during pregnancy may address one piece of the jigsaw of causes of later health and disease.

"One of the surprising findings from our research was that people who had worse mental health throughout their lives had also reached developmental milestones-like standing and walking for the first time-later in life than those who had better mental health."