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Plump babies may really be happier babies, Canadian and British researchers say in a study that found people who have a low birth weight are more likely to have depression and anxiety later in life.
Adverse conditions in the womb that interfere with a baby's growth may also
cause brain differences, the researchers report in the December issue of Biological Psychiatry.
Ian Colman, of the University of Alberta, and colleagues in Britain studied the records of 4600 Britons born in 1946 who took part in a 40-year study.
"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," Mr Colman said.
"It suggests a dose-response relationship. As birth weight progressively decreases, it's more likely that an individual will suffer from mood disorders later in life."
The researchers simply looked at medical records and did not examine a possible cause. Mr Colman says it is possible that when mothers are stressed, stress hormones are passing through the placenta to the fetus.
"One of the surprising findings from our research was, people who had worse mental health throughout their lives had also reached developmental milestones, like standing and walking for the first time, later than those [of] better mental health."
The researchers did not look for any absolute weight but said there was a clear trend.
"As weight at birth increased, the likelihood of symptoms of depression and anxiety across the life course decreased," they wrote.
Not all small babies are fated to have poor mental health, the researchers said, noting that in 1946 records did not indicate whether the children were born prematurely.
"Being born small [is only] a problem if you were born small because of adverse conditions in the womb - and low birth weight is what we looked at because it is considered a marker of stress in the womb," Colman said.
"When a mother is stressed, blood flow to the uterus is restricted and the fetus gets fewer nutrients, which tends to lead to lower birth weight."
"The 'take-home message' of this study is, 'We should take better care of pregnant women'," Mr Colman said.
- REUTERS
