The odds of developing depression or anxiety as an adult may be significantly increased even prior to birth, according to a study led by Ian Colman, assistant professor in the University of Alberta’s School of Public Health.

The study, published in the December 2007 issue of Biological Psychiatry, found that individuals with low birth weights were more likely to become depressed or anxious as adults.

“This [study] shows that prenatal conditions have long-term effects on the developing fetus,” Colman said.

Colman worked with researchers at the University of Cambridge and University College London to discover the correlation between birth weight and mental disorders. The research subjects were all members of the Medical Research Council National Survey of Health and Development, a survey that has monitored symptoms of mental disorder in over 5000 Britons born in 1946.

“We [...] found that babies who were smaller were more likely to be depressed or anxious later on,” Colman said.

Colman further explained why low birth weight may be significant.

“There is biological theory that suggests that when pregnant mothers become stressed [...] there’s less blood flow to the uterus, so the babies aren’t getting nutrients, and they end up smaller.

“[Also,] stress hormones like cortisol are passing through the placenta, and they could influence the developing baby’s brain and permanently alter the stress response in that baby for the rest of its life. So when that baby grows up and is faced with stressful life events, they’re more likely to become depressed or anxious.”

Research that investigates prenatal conditions leads back to that long-standing debate of nature versus nurture.

“I think that what this points to is that nature is an important part of our mental health, and [for] people who suffer from depression and anxiety, this is further evidence that they might be biologically different,” Colman said. “But that doesn’t suggest that the environment isn’t an important factor.”

“This research supports the theory where there’s an interaction between nature and nurture.”