The findings come too late for thousands of future parents who have been striving for a millennium baby. The unofficial race to have a baby on New Year's Day will ensure that thousands more children will be born in January than normal.
The study, presented at the American Psychological Society's annual conference, found that symptoms of depression were more pronounced in people born earlier in the year. The seasonal timing of birth had a stronger impact on women than men.
Experts believe that this predisposition to depression is caused by exposure to environmental changes, stress in the mother and may be linked to seasonal illnesses such as flu. Seasonal viruses contracted by a pregnant woman could be crossing the placental barrier and infecting the developing nervous system of the foetus.
"Stress experienced by the pregnant mother can damage the brain of the developing foetus, possibly due to elevated levels of cortisol," said Mark Richards of Southwest Missouri University's psychology department, who is an author of the study. "Christmas and holidays are very stressful times for many people and the elevated stress levels of the mother could be affecting the unborn child in the final month before birth."
At the beginning of winter people are susceptible to colds and flu, and it is believed that the unborn child is more sensitive during the final months before birth, when the nervous system is developing. "The effects of reduced daylight in the winter months and harsher weather could be affecting the unborn child," he said. Previous research has tentatively suggested that serious illness such as schizophrenia, manic depression, autism and eating disorders are also more common in people born in the winter and spring months.
The 231 people who took part in the study were aged 20 to 29. They were assessed for mild depressive symptoms, using a questionnaire, and their scores correlated against their date of birth. Those born earlier in the year had a greater tendency to show depressive symptoms, and this tapered off towards the end of the year with those born in October, November and December having the least depressive tendencies.Reuse content